Adding upstream version 1:115.7.0.upstream/1%115.7.0upstream

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

212 files changed, 16938 insertions, 0 deletions

diff --git a/thunderbird-l10n/cy/localization/cy/branding/brand.ftl b/thunderbird-l10n/cy/localization/cy/branding/brand.ftl
new file mode 100644
index 0000000000..2026ae846e
--- /dev/null
+++ b/thunderbird-l10n/cy/localization/cy/branding/brand.ftl
@@ -0,0 +1,22 @@
+# This Source Code Form is subject to the terms of the Mozilla Public
+# License, v. 2.0. If a copy of the MPL was not distributed with this
+# file, You can obtain one at http://mozilla.org/MPL/2.0/.
+
+
+## Thunderbird Brand
+##
+## Thunderbird must be treated as a brand, and kept in English.
+## It cannot be:
+## - Transliterated.
+## - Translated.
+##
+## Reference: https://www.mozilla.org/styleguide/communications/translation/
+
+-brand-shorter-name = Thunderbird
+-brand-short-name = Thunderbird
+-brand-full-name = Mozilla Thunderbird
+# This brand name can be used in messages where the product name needs to
+# remain unchanged across different versions (Daily, Beta, etc.).
+-brand-product-name = Thunderbird
+-vendor-short-name = Mozilla
+trademarkInfo = Nodau masnachu'r Mozilla Foundation yw Thunderbird a logos Thunderbird.
diff --git a/thunderbird-l10n/cy/localization/cy/browser/appExtensionFields.ftl b/thunderbird-l10n/cy/localization/cy/browser/appExtensionFields.ftl
new file mode 100644
index 0000000000..e3e9d2afdc
--- /dev/null
+++ b/thunderbird-l10n/cy/localization/cy/browser/appExtensionFields.ftl
@@ -0,0 +1,16 @@
+# This Source Code Form is subject to the terms of the Mozilla Public
+# License, v. 2.0. If a copy of the MPL was not distributed with this
+# file, You can obtain one at http://mozilla.org/MPL/2.0/.
+
+
+## Theme names and descriptions used in the Themes panel in about:addons
+
+# "Auto" is short for automatic. It can be localized without limitations.
+extension-default-theme-name-auto = Thema'r system — awto
+extension-default-theme-description = Dilynwch osodiadau'r system weithredu am fotymau, dewislenni a ffenestri.
+
+extension-thunderbird-compact-light-name = Golau
+extension-thunderbird-compact-light-description = Thema gyda chynllun lliw golau.
+
+extension-thunderbird-compact-dark-name = Tywyll
+extension-thunderbird-compact-dark-description = Thema sydd â chynllun lliw tywyll.
diff --git a/thunderbird-l10n/cy/localization/cy/browser/branding/brandings.ftl b/thunderbird-l10n/cy/localization/cy/browser/branding/brandings.ftl
new file mode 100644
index 0000000000..9ada8da73a
--- /dev/null
+++ b/thunderbird-l10n/cy/localization/cy/browser/branding/brandings.ftl
@@ -0,0 +1,18 @@
+# This Source Code Form is subject to the terms of the Mozilla Public
+# License, v. 2.0. If a copy of the MPL was not distributed with this
+# file, You can obtain one at http://mozilla.org/MPL/2.0/.
+
+
+## The following feature names must be treated as a brand.
+##
+## They cannot be:
+## - Transliterated.
+## - Translated.
+##
+## Declension should be avoided where possible, leaving the original
+## brand unaltered in prominent UI positions.
+##
+## For further details, consult:
+## https://mozilla-l10n.github.io/styleguides/mozilla_general/#brands-copyright-and-trademark
+
+-profiler-brand-name = Firefox Profiler
diff --git a/thunderbird-l10n/cy/localization/cy/browser/components/mozFiveStar.ftl b/thunderbird-l10n/cy/localization/cy/browser/components/mozFiveStar.ftl
new file mode 100644
index 0000000000..e350dec840
--- /dev/null
+++ b/thunderbird-l10n/cy/localization/cy/browser/components/mozFiveStar.ftl
@@ -0,0 +1,9 @@
+# This Source Code Form is subject to the terms of the Mozilla Public
+# License, v. 2.0. If a copy of the MPL was not distributed with this
+# file, You can obtain one at http://mozilla.org/MPL/2.0/.
+
+# The rating out of 5 stars.
+# Variables:
+#   $rating (number) - A number between 0 and 5. The translation should show at most one digit after the comma.
+moz-five-star-rating =
+    .title = Graddiwyd { NUMBER($rating, maximumFractionDigits: 1) } allan o 5
diff --git a/thunderbird-l10n/cy/localization/cy/browser/components/mozSupportLink.ftl b/thunderbird-l10n/cy/localization/cy/browser/components/mozSupportLink.ftl
new file mode 100644
index 0000000000..e7717be948
--- /dev/null
+++ b/thunderbird-l10n/cy/localization/cy/browser/components/mozSupportLink.ftl
@@ -0,0 +1,5 @@
+# This Source Code Form is subject to the terms of the Mozilla Public
+# License, v. 2.0. If a copy of the MPL was not distributed with this
+# file, You can obtain one at http://mozilla.org/MPL/2.0/.
+
+moz-support-link-text = Dysgu rhagor
diff --git a/thunderbird-l10n/cy/localization/cy/calendar/calendar-context-menus.ftl b/thunderbird-l10n/cy/localization/cy/calendar/calendar-context-menus.ftl
new file mode 100644
index 0000000000..b7efea3882
--- /dev/null
+++ b/thunderbird-l10n/cy/localization/cy/calendar/calendar-context-menus.ftl
@@ -0,0 +1,10 @@
+# This Source Code Form is subject to the terms of the Mozilla Public
+# License, v. 2.0. If a copy of the MPL was not distributed with this
+# file, You can obtain one at http://mozilla.org/MPL/2.0/.
+
+list-calendar-context-reload-menuitem =
+    .label = Cydweddu
+    .accesskey = C
+calendar-item-context-menu-modify-menuitem =
+    .label = Golygu
+    .accesskey = G
diff --git a/thunderbird-l10n/cy/localization/cy/calendar/calendar-delete-prompt.ftl b/thunderbird-l10n/cy/localization/cy/calendar/calendar-delete-prompt.ftl
new file mode 100644
index 0000000000..712f05e09b
--- /dev/null
+++ b/thunderbird-l10n/cy/localization/cy/calendar/calendar-delete-prompt.ftl
@@ -0,0 +1,59 @@
+# This Source Code Form is subject to the terms of the Mozilla Public
+# License, v. 2.0. If a copy of the MPL was not distributed with this
+# file, You can obtain one at http://mozilla.org/MPL/2.0/.
+
+calendar-delete-event-prompt-title =
+    { $count ->
+        [zero] Dileu Digwyddiadau
+        [one] Dileu Digwyddiad
+        [two] Dileu Digwyddiad
+        [few] Dileu Digwyddiad
+        [many] Dileu Digwyddiad
+       *[other] Dileu Digwyddiad
+    }
+calendar-delete-event-prompt-message =
+    { $count ->
+        [zero] Ydych chi wir eisiau dileu'r digwyddiadau yma?
+        [one] Ydych chi wir eisiau dileu'r digwyddiad yma?
+        [two] Ydych chi wir eisiau dileu'r { $count } digwyddiad yma?
+        [few] Ydych chi wir eisiau dileu'r { $count } digwyddiad yma?
+        [many] Ydych chi wir eisiau dileu'r { $count } digwyddiad yma?
+       *[other] Ydych chi wir eisiau dileu'r { $count } digwyddiad yma?
+    }
+calendar-delete-task-prompt-title =
+    { $count ->
+        [zero] Dileu Tasgau
+        [one] Dileu Tasg
+        [two] Dileu Tasg
+        [few] Dileu Tasg
+        [many] Dileu Tasg
+       *[other] Dileu Tasg
+    }
+calendar-delete-task-prompt-message =
+    { $count ->
+        [zero] Ydych chi wir eisiau dileu'r digwyddiadau yma?
+        [one] Ydych chi wir eisiau dileu'r digwyddiad yma?
+        [two] Ydych chi wir eisiau dileu'r { $count } digwyddiad yma?
+        [few] Ydych chi wir eisiau dileu'r { $count } digwyddiad yma?
+        [many] Ydych chi wir eisiau dileu'r { $count } digwyddiad yma?
+       *[other] Ydych chi wir eisiau dileu'r { $count } digwyddiad yma?
+    }
+calendar-delete-item-prompt-title =
+    { $count ->
+        [zero] Dileu Eitemau
+        [one] Dileu Eitem
+        [two] Dileu Eitem
+        [few] Dileu Eitem
+        [many] Dileu Eitem
+       *[other] Dileu Eitem
+    }
+calendar-delete-item-prompt-message =
+    { $count ->
+        [zero] Ydych chi wir eisiau dileu'r eitemau yma?
+        [one] Ydych chi wir eisiau dileu'r eitem yma?
+        [two] Ydych chi wir eisiau dileu'r { $count } eitem yma?
+        [few] Ydych chi wir eisiau dileu'r { $count } eitem yma?
+        [many] Ydych chi wir eisiau dileu'r { $count } eitem yma?
+       *[other] Ydych chi wir eisiau dileu'r { $count } eitem yma?
+    }
+calendar-delete-prompt-disable-message = Peidiwch gofyn i mi eto
diff --git a/thunderbird-l10n/cy/localization/cy/calendar/calendar-editable-item.ftl b/thunderbird-l10n/cy/localization/cy/calendar/calendar-editable-item.ftl
new file mode 100644
index 0000000000..c4bef87475
--- /dev/null
+++ b/thunderbird-l10n/cy/localization/cy/calendar/calendar-editable-item.ftl
@@ -0,0 +1,30 @@
+# This Source Code Form is subject to the terms of the Mozilla Public
+# License, v. 2.0. If a copy of the MPL was not distributed with this
+# file, You can obtain one at http://mozilla.org/MPL/2.0/.
+
+calendar-editable-item-privacy-icon-private =
+    .alt = Preifatrwydd: Digwyddiad Preifat
+calendar-editable-item-privacy-icon-confidential =
+    .alt = Preifatrwydd: Dangos Amser a Dyddiad yn Unig
+calendar-editable-item-recurrence =
+    .alt = Yn ailadrodd
+calendar-editable-item-recurrence-exception =
+    .alt = Eithriad ailadrodd
+calendar-editable-item-todo-icon-task =
+    .alt = Tasg
+calendar-editable-item-todo-icon-completed-task =
+    .alt = Tasg wedi'i chwblhau
+calendar-editable-item-multiday-event-icon-start =
+    .alt = Digwyddiad diwrnod lluosog yn cychwyn
+calendar-editable-item-multiday-event-icon-continue =
+    .alt = Digwyddiad diwrnod lluosog yn parhau
+calendar-editable-item-multiday-event-icon-end =
+    .alt = Digwyddiad diwrnod lluosog yn gorffen
+calendar-editable-item-reminder-icon-alarm =
+    .alt = Mae rhybudd atgoffa wedi'i drefnu
+calendar-editable-item-reminder-icon-suppressed-alarm =
+    .alt = Mae rhybudd atgoffa wedi'i drefnu ond ar hyn o bryd yn cael ei atal
+calendar-editable-item-reminder-icon-email =
+    .alt = Mae e-bost atgoffa wedi'i drefnu
+calendar-editable-item-reminder-icon-audio =
+    .alt = Mae rhybudd atgoffa wedi'i drefnu
diff --git a/thunderbird-l10n/cy/localization/cy/calendar/calendar-event-dialog-reminder.ftl b/thunderbird-l10n/cy/localization/cy/calendar/calendar-event-dialog-reminder.ftl
new file mode 100644
index 0000000000..54889ad27d
--- /dev/null
+++ b/thunderbird-l10n/cy/localization/cy/calendar/calendar-event-dialog-reminder.ftl
@@ -0,0 +1,10 @@
+# This Source Code Form is subject to the terms of the Mozilla Public
+# License, v. 2.0. If a copy of the MPL was not distributed with this
+# file, You can obtain one at http://mozilla.org/MPL/2.0/.
+
+calendar-event-reminder-icon-display =
+    .alt = Dangos Rhybudd
+calendar-event-reminder-icon-email =
+    .alt = Anfon E-bost
+calendar-event-reminder-icon-audio =
+    .alt = Chwarae Rhybudd sain
diff --git a/thunderbird-l10n/cy/localization/cy/calendar/calendar-event-listing.ftl b/thunderbird-l10n/cy/localization/cy/calendar/calendar-event-listing.ftl
new file mode 100644
index 0000000000..cdb50bf9d1
--- /dev/null
+++ b/thunderbird-l10n/cy/localization/cy/calendar/calendar-event-listing.ftl
@@ -0,0 +1,71 @@
+# This Source Code Form is subject to the terms of the Mozilla Public
+# License, v. 2.0. If a copy of the MPL was not distributed with this
+# file, You can obtain one at http://mozilla.org/MPL/2.0/.
+
+calendar-event-listing-close =
+    .tooltiptext = Cau chwilio digwyddiadau a rhestr digwyddiadau
+
+## Listing columns
+
+calendar-event-listing-column-calendar-name =
+    .label = Enw Calendr
+    .tooltiptext = Trefnu yn ôl enw calendr
+calendar-event-listing-column-category =
+    .label = Categori
+    .tooltiptext = Trefnu yn ôl categori
+# This label and tooltip is used for the column with the checkbox in the task
+# tree view, which indicates whether a task has been marked as completed.
+calendar-event-listing-column-completed =
+    .label = Gorffen
+    .tooltiptext = Trefnu yn ôl eu cwblhau
+calendar-event-listing-column-completed-date =
+    .label = Cwblhawyd
+    .tooltiptext = Trefnu yn ôl dyddiad cwblhau
+calendar-event-listing-column-due-date =
+    .label = Erbyn
+    .tooltiptext = Trefnu yn ôl diwrnod y digwyddiad
+calendar-event-listing-column-end-date =
+    .label = Diwedd
+    .tooltiptext = Trefnu yn ôl dyddiad diwedd
+calendar-event-listing-column-location =
+    .label = Lleoliad
+    .tooltiptext = Trefnu yn ôl lleoliad
+calendar-event-listing-column-percent-complete =
+    .label = Cwblhawyd %
+    .tooltiptext = Trefnu yn ôl % wedi'u cwblhau
+calendar-event-listing-column-priority =
+    .label = Blaenoriaeth
+    .tooltiptext = Trefnu yn ôl blaenoriaeth
+calendar-event-listing-column-start-date =
+    .label = Cychwyn
+    .tooltiptext = Trefnu yn ôl dyddiad cychwyn
+calendar-event-listing-column-status =
+    .label = Statws
+    .tooltiptext = Trefnu yn ôl statws
+calendar-event-listing-column-time-until-due =
+    .label = Cwblhau ymhen
+    .tooltiptext = Trefnu yn ôl cyfnod hyd y digwyddiad
+calendar-event-listing-column-title =
+    .label = Teitl
+    .tooltiptext = Trefnu yn ôl teitl
+
+## Interval dropdown options
+
+calendar-event-listing-interval-calendar-month =
+    .label = Digwyddiadau yn ystod y Mis Calendr yma
+calendar-event-listing-interval-current-view =
+    .label = Digwyddiadau yn y Golwg Gyfredol
+calendar-event-listing-interval-next-7-days =
+    .label = Digwyddiadau yn ystod y 7 Diwrnod Nesaf
+calendar-event-listing-interval-next-14-days =
+    .label = Digwyddiadau yn ystod y 14 Diwrnod Nesaf
+calendar-event-listing-interval-next-31-days =
+    .label = Digwyddiadau yn ystod y 31 Diwrnod Nesaf
+calendar-event-listing-interval-next-6-months =
+    .label = Digwyddiadau yn Ystod y 6 Mis Nesaf
+calendar-event-listing-interval-next-12-months =
+    .label = Digwyddiadau yn Ystod y 12 Mis Nesaf
+calendar-event-listing-interval-selected-day =
+    .label = Diwrnod Cyfredol wedi'i Ddewis
+calendar-event-listing-interval-today =
+    .label = Digwyddiadau Heddiw
diff --git a/thunderbird-l10n/cy/localization/cy/calendar/calendar-ics-file-dialog.ftl b/thunderbird-l10n/cy/localization/cy/calendar/calendar-ics-file-dialog.ftl
new file mode 100644
index 0000000000..064ad9ac4f
--- /dev/null
+++ b/thunderbird-l10n/cy/localization/cy/calendar/calendar-ics-file-dialog.ftl
@@ -0,0 +1,58 @@
+# This Source Code Form is subject to the terms of the Mozilla Public
+# License, v. 2.0. If a copy of the MPL was not distributed with this
+# file, You can obtain one at http://mozilla.org/MPL/2.0/.
+
+calendar-ics-file-window-2 =
+    .title = Mewnforio Digwyddiadau a Thasgau Calendr
+calendar-ics-file-window-title = Mewnforio Digwyddiadau a Thasgau Calendr
+calendar-ics-file-dialog-import-event-button-label = Mewnforio Digwyddiadau
+calendar-ics-file-dialog-import-task-button-label = Mewnforio Tasg
+calendar-ics-file-dialog-2 =
+    .buttonlabelaccept = Mewnforio'r Cyfan
+calendar-ics-file-accept-button-ok-label = Iawn
+calendar-ics-file-cancel-button-close-label = Cau
+calendar-ics-file-dialog-message-2 = Mewnforio o'r ffeil:
+calendar-ics-file-dialog-calendar-menu-label = Mewnforio i'r calendr:
+calendar-ics-file-dialog-items-loading-message =
+    .value = Wrthi'n llwytho eitemau…
+calendar-ics-file-dialog-search-input =
+    .placeholder = Hidlo eitemau…
+calendar-ics-file-dialog-sort-start-ascending =
+    .label = Trefnu yn ôl y dyddiad cychwyn (y cyntaf i'r olaf)
+calendar-ics-file-dialog-sort-start-descending =
+    .label = Trefnu yn ôl y dyddiad cychwyn (y cyntaf i'r olaf)
+# "A > Z" is used as a concise way to say "alphabetical order".
+# You may replace it with something appropriate to your language.
+calendar-ics-file-dialog-sort-title-ascending =
+    .label = Trefnu yn ôl teitl (A > Z)
+# "Z > A" is used as a concise way to say "reverse alphabetical order".
+# You may replace it with something appropriate to your language.
+calendar-ics-file-dialog-sort-title-descending =
+    .label = Trefnu yn ôl teitl (A > Z)
+calendar-ics-file-dialog-progress-message = Mewnforio…
+calendar-ics-file-import-success = Wedi’i mewnforio’n llwyddiannus
+calendar-ics-file-import-error = Digwyddodd gwall a methodd y mewnforio.
+calendar-ics-file-import-complete = Mewnforio wedi'i gwblhau.
+# Variables:
+# $duplicatesCount (Number) - Number of items already existing in the target calendar.
+calendar-ics-file-import-duplicates =
+    { $duplicatesCount ->
+        [zero] Anwybyddwyd dim eitemau.
+        [one] Anwybyddwyd un eitem gan ei bod eisoes yn bodoli yn y calendr cyrchfan.
+        [two] Anwybyddwyd { $duplicatesCount } eitem gan eu bod eisoes yn bodoli yn y calendr cyrchfan.
+        [few] Anwybyddwyd { $duplicatesCount } eitem gan eu bod eisoes yn bodoli yn y calendr cyrchfan.
+        [many] Anwybyddwyd { $duplicatesCount } eitem gan eu bod eisoes yn bodoli yn y calendr cyrchfan.
+       *[other] Anwybyddwyd { $duplicatesCount } eitem gan eu bod eisoes yn bodoli yn y calendr cyrchfan.
+    }
+# Variables:
+# $errorsCount (Number) - Number of errors while importing ics file.
+calendar-ics-file-import-errors =
+    { $errorsCount ->
+        [zero] Methodd mewnforio dim eitemau.
+        [one] Methodd mewnforio un eitem. Gwiriwch y Consol Gwall am fanylion.
+        [two] Methodd mewnforio { $errorCount } eitem. Gwiriwch y Consol Gwall am fanylion.
+        [few] Methodd mewnforio { $errorCount } eitem. Gwiriwch y Consol Gwall am fanylion.
+        [many] Methodd mewnforio { $errorCount } eitem. Gwiriwch y Consol Gwall am fanylion.
+       *[other] Methodd mewnforio { $errorCount } eitem. Gwiriwch y Consol Gwall am fanylion.
+    }
+calendar-ics-file-dialog-no-calendars = Nid oes unrhyw galendrau sy'n gallu mewnforio digwyddiadau neu dasgau.
diff --git a/thunderbird-l10n/cy/localization/cy/calendar/calendar-invitation-panel.ftl b/thunderbird-l10n/cy/localization/cy/calendar/calendar-invitation-panel.ftl
new file mode 100644
index 0000000000..b2cb36f7ca
--- /dev/null
+++ b/thunderbird-l10n/cy/localization/cy/calendar/calendar-invitation-panel.ftl
@@ -0,0 +1,115 @@
+# This Source Code Form is subject to the terms of the Mozilla Public
+# License, v. 2.0. If a copy of the MPL was not distributed with this
+# file, You can obtain one at http://mozilla.org/MPL/2.0/.
+
+# Variables:
+# $organizer (String) - The participant that created the original invitation.
+calendar-invitation-panel-intro = Mae { $organizer } wedi eich gwahodd i:
+calendar-invitation-panel-status-new = Rydych wedi cael gwahoddiad i'r digwyddiad hwn.
+calendar-invitation-panel-status-processed = Mae'r digwyddiad hwn wedi ei ychwanegu i'ch calendr.
+calendar-invitation-panel-status-updateminor = Mae'r neges hon yn cynnwys gwybodaeth am y ddigwyddiad hwn.
+calendar-invitation-panel-status-updatemajor = Mae'r neges hon yn cynnwys diweddariad am y digwyddiad hwn. Dylech ail-gadarnhau eich presenoldeb.
+calendar-invitation-panel-status-cancelled = Mae'r neges hon yn cynnwys diddymiad ar gyfer y digwyddiad hwn.
+calendar-invitation-panel-status-cancelled-notfound = Mae'r neges hon yn cynnwys diddymiad ar gyfer digwyddiad nad yw ar eich calendr.
+# Variables:
+# $organizer (String) - The participant that cancelled the invitation.
+calendar-invitation-panel-intro-cancel = Mae { $organizer } wedi diddymu:
+# Variables:
+# $summary (String) - A short summary or title of the event.
+calendar-invitation-panel-title = { $summary }
+calendar-invitation-panel-action-button = Cadw
+calendar-invitation-panel-view-button = Golwg
+calendar-invitation-panel-update-button = Diweddaru
+calendar-invitation-panel-delete-button = Dileu
+calendar-invitation-panel-accept-button = Iawn
+calendar-invitation-panel-decline-button = Na
+calendar-invitation-panel-tentative-button = Efallai
+calendar-invitation-panel-reply-status = * Nid ydych wedi penderfynu nac ymateb eto
+calendar-invitation-panel-more-button = Rhagor
+calendar-invitation-panel-menu-item-save =
+    .label = Cadw i galendr
+calendar-invitation-panel-menu-item-save-copy =
+    .label = Cadw copi
+calendar-invitation-panel-menu-item-toggle-changes =
+    .label = Dangos Newidiadau
+calendar-invitation-panel-prop-title-when = Pryd:
+calendar-invitation-panel-prop-title-location = Lleoliad:
+# Variables:
+# $dayOfWeek (String) - The day of the week for a given date.
+# $date (String) - The date example: Tuesday, February 24, 2022.
+calendar-invitation-datetime-date = { $dayOfWeek }, { $date }
+# Variables:
+# $time (String) - The time part of a datetime using the "short" timeStyle.
+# $timezone (String) - The timezone info for the datetime.
+calendar-invitation-datetime-time = { $time } ({ $timezone })
+# Example: Friday, September 16, 2022
+# Variables:
+# $startDate (String) - The date (without time) the event starts on.
+calendar-invitation-interval-all-day = { $startDate }
+# Example: September 16, 2022 – September 16, 2023
+# Variables:
+# $startMonth (String) - The month the interval starts.
+# $startDay   (String) - The day of the month the interval starts.
+# $startYear  (String) - The year the interval starts.
+# $endMonth   (String) - The month the interval ends.
+# $endDay     (String) - The day of the month the interval ends.
+# $endYear    (String) - The year the interval ends.
+calendar-invitation-interval-all-day-between-years = { $startMonth } { $startDay }, { $startYear } – { $endMonth } { $endDay }, { $endYear }
+# Example: September 16 – 20, 2022
+# Variables:
+# $month      (String) - The month the interval is in.
+# $startDay   (String) - The day of the month the interval starts.
+# $endDay     (String) - The day of the month the interval ends.
+# $year       (String) - The year the interval is in.
+calendar-invitation-interval-all-day-in-month = { $month } { $startDay } – { $endDay }, { $year }
+# Example: September 16 – October 20, 2022
+# Variables:
+# $startMonth (String) - The month the interval starts.
+# $startDay   (String) - The day of the month the interval starts.
+# $endMonth   (String) - The month the interval ends.
+# $endDay     (String) - The day of the month the interval ends.
+# $year       (String) - The year the interval is in.
+calendar-invitation-interval-all-day-between-months = { $startMonth } { $startDay } – { $endMonth } { $endDay }, { $year }
+# Example: Friday, September 16, 2022 15:00 America/Port of Spain
+# Variables:
+# $startDate (String) - The date the interval starts.
+# $startTime (String) - The time the interval starts.
+# $timezone  (String) - The timezone the interval is in.
+calendar-invitation-interval-same-date-time = { $startDate } <b>{ $startTime }</b> { $timezone }
+# Example: Friday, September 16, 2022 14:00 – 16:00 America/Port of Spain
+# Variables:
+# $startDate (String) - The date the interval starts.
+# $startTime (String) - The time the interval starts.
+# $endTime   (String) - The time the interval ends.
+# $timezone  (String) - The timezone the interval is in.
+calendar-invitation-interval-same-day = { $startDate } <b>{ $startTime }</b> – <b>{ $endTime }</b> { $timezone }
+# Example: Friday, September 16, 2022 14:00 – Tuesday, September 20, 2022 16:00 America/Port of Spain
+# Variables:
+# $startDate (String) - The date the interval starts.
+# $startTime (String) - The time the interval starts.
+# $endDate   (String) - The date the interval ends.
+# $endTime   (String) - The time the interval ends.
+# $timezone  (String) - The timezone the interval is in.
+calendar-invitation-interval-several-days = { $startDate } <b>{ $startTime }</b> – { $endDate } <b>{ $endTime }</b> { $timezone }
+calendar-invitation-panel-prop-title-recurrence = Yn ailadrodd:
+calendar-invitation-panel-prop-title-attendees = Mynychwyr:
+calendar-invitation-panel-prop-title-description = Disgrifiad:
+# Variables:
+# $count (Number) - The number of attendees with the "ACCEPTED" participation status.
+calendar-invitation-panel-partstat-accepted = { $count } iawn
+# Variables:
+# $count (Number) - The number of attendees with the "DECLINED" participation status.
+calendar-invitation-panel-partstat-declined = { $count } na
+# Variables:
+# $count (Number) - The number of attendees with the "TENTATIVE" participation status.
+calendar-invitation-panel-partstat-tentative = { $count } efallai
+# Variables:
+# $count (Number) - The number of attendees with the "NEEDS-ACTION" participation status.
+calendar-invitation-panel-partstat-needs-action = { $count } yn aros penderfyniad
+# Variables:
+# $count (Number) - The total number of attendees.
+calendar-invitation-panel-partstat-total = { $count } mynychwr
+calendar-invitation-panel-prop-title-attachments = Atodiadau:
+calendar-invitation-change-indicator-removed = Wedi'i ddileu
+calendar-invitation-change-indicator-added = Newydd
+calendar-invitation-change-indicator-modified = Newidiwyd
diff --git a/thunderbird-l10n/cy/localization/cy/calendar/calendar-invitations-dialog.ftl b/thunderbird-l10n/cy/localization/cy/calendar/calendar-invitations-dialog.ftl
new file mode 100644
index 0000000000..399cdb2e56
--- /dev/null
+++ b/thunderbird-l10n/cy/localization/cy/calendar/calendar-invitations-dialog.ftl
@@ -0,0 +1,10 @@
+# This Source Code Form is subject to the terms of the Mozilla Public
+# License, v. 2.0. If a copy of the MPL was not distributed with this
+# file, You can obtain one at http://mozilla.org/MPL/2.0/.
+
+calendar-invitation-current-participation-status-icon-accepted =
+    .alt = Wedi'i derbyn ar hyn o bryd
+calendar-invitation-current-participation-status-icon-declined =
+    .alt = Wedi'i gwrthod ar hyn o bryd
+calendar-invitation-current-participation-status-icon-needs-action =
+    .alt = Heb benderfynnu ar hyn o bryd
diff --git a/thunderbird-l10n/cy/localization/cy/calendar/calendar-itip-identity-dialog.ftl b/thunderbird-l10n/cy/localization/cy/calendar/calendar-itip-identity-dialog.ftl
new file mode 100644
index 0000000000..8a50aa0d9f
--- /dev/null
+++ b/thunderbird-l10n/cy/localization/cy/calendar/calendar-itip-identity-dialog.ftl
@@ -0,0 +1,8 @@
+# This Source Code Form is subject to the terms of the Mozilla Public
+# License, v. 2.0. If a copy of the MPL was not distributed with this
+# file, You can obtain one at http://mozilla.org/MPL/2.0/.
+
+calendar-itip-identity-dialog-title = Mynd heb wahoddiad?
+calendar-itip-identity-warning = Nid ydych ar y rhestr westeion eto.
+calendar-itip-identity-label = Ymateb fel:
+calendar-itip-identity-label-none = Cysylltwch y digwyddiad hwn â:
diff --git a/thunderbird-l10n/cy/localization/cy/calendar/calendar-print.ftl b/thunderbird-l10n/cy/localization/cy/calendar/calendar-print.ftl
new file mode 100644
index 0000000000..8ae340a792
--- /dev/null
+++ b/thunderbird-l10n/cy/localization/cy/calendar/calendar-print.ftl
@@ -0,0 +1,17 @@
+# This Source Code Form is subject to the terms of the Mozilla Public
+# License, v. 2.0. If a copy of the MPL was not distributed with this
+# file, You can obtain one at http://mozilla.org/MPL/2.0/.
+
+calendar-print-layout-label = Cynllun
+calendar-print-layout-list = Rhestr
+calendar-print-layout-month-grid = Grid Misol
+calendar-print-layout-week-planner = Cynllunydd Wythnos
+calendar-print-filter-label = Beth i'w Argraffu
+calendar-print-filter-events = Digwyddiadau
+calendar-print-filter-tasks = Tasgau
+calendar-print-filter-completedtasks = Tasgau wedi'u cwblhau
+calendar-print-filter-taskswithnoduedate = Tasgau heb ddyddiad cwblhau
+calendar-print-range-from = O
+calendar-print-range-to = Tan
+calendar-print-back-button = Nôl
+calendar-print-next-button = Nesaf
diff --git a/thunderbird-l10n/cy/localization/cy/calendar/calendar-recurrence-dialog.ftl b/thunderbird-l10n/cy/localization/cy/calendar/calendar-recurrence-dialog.ftl
new file mode 100644
index 0000000000..83a36cc6fd
--- /dev/null
+++ b/thunderbird-l10n/cy/localization/cy/calendar/calendar-recurrence-dialog.ftl
@@ -0,0 +1,8 @@
+# This Source Code Form is subject to the terms of the Mozilla Public
+# License, v. 2.0. If a copy of the MPL was not distributed with this
+# file, You can obtain one at http://mozilla.org/MPL/2.0/.
+
+calendar-recurrence-preview-label = Rhagolwg
+calendar-recurrence-next = Mis Nesaf
+calendar-recurrence-previous = Mis Blaenorol
+calendar-recurrence-today = Heddiw
diff --git a/thunderbird-l10n/cy/localization/cy/calendar/calendar-summary-dialog.ftl b/thunderbird-l10n/cy/localization/cy/calendar/calendar-summary-dialog.ftl
new file mode 100644
index 0000000000..76f23af021
--- /dev/null
+++ b/thunderbird-l10n/cy/localization/cy/calendar/calendar-summary-dialog.ftl
@@ -0,0 +1,17 @@
+# This Source Code Form is subject to the terms of the Mozilla Public
+# License, v. 2.0. If a copy of the MPL was not distributed with this
+# file, You can obtain one at http://mozilla.org/MPL/2.0/.
+
+calendar-summary-dialog-edit-button =
+    .label = Golygu
+    .accesskey = G
+calendar-summary-dialog-edit-menu-button =
+    .label = Golygu
+edit-button-context-menu-this-occurrence =
+    .label = Golygu dim ond y digwyddiad yma
+    .accesskey = d
+edit-button-context-menu-all-occurrences =
+    .label = Golygu pob enghraifft
+    .accesskey = e
+description-context-menu-copy-link-text =
+    .label = Copïo Testun Dolen
diff --git a/thunderbird-l10n/cy/localization/cy/calendar/calendar-uri-redirect-dialog.ftl b/thunderbird-l10n/cy/localization/cy/calendar/calendar-uri-redirect-dialog.ftl
new file mode 100644
index 0000000000..6d60d4319e
--- /dev/null
+++ b/thunderbird-l10n/cy/localization/cy/calendar/calendar-uri-redirect-dialog.ftl
@@ -0,0 +1,12 @@
+# This Source Code Form is subject to the terms of the Mozilla Public
+# License, v. 2.0. If a copy of the MPL was not distributed with this
+# file, You can obtain one at http://mozilla.org/MPL/2.0/.
+
+calendar-uri-redirect-window =
+    .title = Ailgyfeirio URI Calendr
+calendar-uri-redirect-window-title = Ailgyfeirio URI Calendr
+calendar-uri-redirect-description =
+    Mae'r gweinydd yn ailgyfeirio URI calendr "{ $calendarName }".
+    Derbyn yr ailgyfeirio a dechrau defnyddio'r URI newydd ar gyfer y calendr hwn?
+calendar-uri-redirect-original-uri-label = URI cyfredol:
+calendar-uri-redirect-target-uri-label = Ailgyfeirio i URI newydd:
diff --git a/thunderbird-l10n/cy/localization/cy/calendar/calendar-widgets.ftl b/thunderbird-l10n/cy/localization/cy/calendar/calendar-widgets.ftl
new file mode 100644
index 0000000000..ec6b2d6339
--- /dev/null
+++ b/thunderbird-l10n/cy/localization/cy/calendar/calendar-widgets.ftl
@@ -0,0 +1,111 @@
+# This Source Code Form is subject to the terms of the Mozilla Public
+# License, v. 2.0. If a copy of the MPL was not distributed with this
+# file, You can obtain one at http://mozilla.org/MPL/2.0/.
+
+calendar-deactivated-notification-events = Mae pob calendr wedi'i analluogi ar hyn o bryd. Galluogwch galendr sy'n bodoli eisoes neu ychwanegu un newydd i greu a golygu digwyddiadau.
+calendar-deactivated-notification-tasks = Mae pob calendr wedi'i analluogi ar hyn o bryd. Galluogwch galendr sy'n bodoli eisoes neu ychwanegu un newydd i greu a golygu tasgau.
+calendar-notifications-label = Dangos hysbysiadau ar gyfer digwyddiadau sydd i ddod
+calendar-add-notification-button =
+    .label = Ychwanegu hysbysiad
+
+## Side panel
+
+calendar-list-header = Calendrau
+# Variables:
+#  $calendarName (String) - Calendar name as given by the user
+calendar-no-reminders-tooltip =
+    .title = Mae calendr { $calendarName } wedi'i dewi
+calendar-enable-button = Galluogi
+# Variables:
+#  $calendarName (String) - Calendar name as given by the user
+calendar-list-item-context-button =
+    .title = Dewisiadau calendr { $calendarName }
+calendar-import-new-calendar = Calendr Newydd…
+    .title = Crëwch neu danysgrifio i galendr newydd
+calendar-refresh-calendars =
+    .title = Ail-lwytho pob calendr a chydweddu newidiadau
+calendar-new-event-primary-button = Digwyddiad Newydd
+calendar-new-task-primary-button = Tasg Newydd
+
+## Calendar navigation
+
+calendar-nav-button-prev-tooltip-day =
+    .title = Diwrnod Blaenorol
+    .accesskey = B
+calendar-nav-button-prev-tooltip-week =
+    .title = Wythnos Flaenorol
+    .accesskey = F
+calendar-nav-button-prev-tooltip-multiweek =
+    .title = Wythnos Flaenorol
+    .accesskey = F
+calendar-nav-button-prev-tooltip-month =
+    .title = Mis Blaenorol
+    .accesskey = B
+calendar-nav-button-prev-tooltip-year =
+    .title = Blwyddyn Flaenorol
+    .accesskey = B
+calendar-nav-button-next-tooltip-day =
+    .title = Diwrnod Nesaf
+    .accesskey = N
+calendar-nav-button-next-tooltip-week =
+    .title = Wythnos Nesaf
+    .accesskey = N
+calendar-nav-button-next-tooltip-multiweek =
+    .title = Wythnos Nesaf
+    .accesskey = N
+calendar-nav-button-next-tooltip-month =
+    .title = Mis Nesaf
+    .accesskey = N
+calendar-nav-button-next-tooltip-year =
+    .title = Blwyddyn Nesaf
+    .accesskey = N
+calendar-today-button-tooltip =
+    .title = Mynd i Heddiw
+calendar-view-toggle-day = Diwrnod
+    .title = Newid i golwg diwrnod
+calendar-view-toggle-week = Wythnos
+    .title = Newid i golwg wythnos
+calendar-view-toggle-multiweek = Wythnosau
+    .title = Newid i golwg wythnosol
+calendar-view-toggle-month = Mis
+    .title = Newid i golwg mis
+
+## Menu on calendar control bar
+
+calendar-control-bar-menu-button =
+    .title = Dewisiadau cynllun calendr
+calendar-find-events-menu-option =
+    .label = Canfod Paen Digwyddiadau
+calendar-hide-weekends-option =
+    .label = Dyddiau'r wythnos waith yn unig
+calendar-define-workweek-option =
+    .label = Diffinio diwrnodau gwaith yr wythnos
+calendar-show-tasks-calendar-option =
+    .label = Dangos tasgau yn y calendr
+
+## Calendar Context Menu
+
+calendar-context-menu-previous-day =
+    .label = Diwrnod Blaenorol
+    .accesskey = B
+calendar-context-menu-previous-week =
+    .label = Wythnos Flaenorol
+    .accesskey = F
+calendar-context-menu-previous-multiweek =
+    .label = Wythnos Flaenorol
+    .accesskey = F
+calendar-context-menu-previous-month =
+    .label = Mis Blaenorol
+    .accesskey = l
+calendar-context-menu-next-day =
+    .label = Diwrnod Nesaf
+    .accesskey = N
+calendar-context-menu-next-week =
+    .label = Wythnos Nesaf
+    .accesskey = W
+calendar-context-menu-next-multiweek =
+    .label = Wythnos Nesaf
+    .accesskey = W
+calendar-context-menu-next-month =
+    .label = Mis Nesaf
+    .accesskey = M
diff --git a/thunderbird-l10n/cy/localization/cy/calendar/category-dialog.ftl b/thunderbird-l10n/cy/localization/cy/calendar/category-dialog.ftl
new file mode 100644
index 0000000000..671344e375
--- /dev/null
+++ b/thunderbird-l10n/cy/localization/cy/calendar/category-dialog.ftl
@@ -0,0 +1,7 @@
+# This Source Code Form is subject to the terms of the Mozilla Public
+# License, v. 2.0. If a copy of the MPL was not distributed with this
+# file, You can obtain one at http://mozilla.org/MPL/2.0/.
+
+category-name-label = Enw
+category-color-label =
+    .label = Defnyddio Lliw
diff --git a/thunderbird-l10n/cy/localization/cy/calendar/preferences.ftl b/thunderbird-l10n/cy/localization/cy/calendar/preferences.ftl
new file mode 100644
index 0000000000..004112c4cd
--- /dev/null
+++ b/thunderbird-l10n/cy/localization/cy/calendar/preferences.ftl
@@ -0,0 +1,192 @@
+# This Source Code Form is subject to the terms of the Mozilla Public
+# License, v. 2.0. If a copy of the MPL was not distributed with this
+# file, You can obtain one at http://mozilla.org/MPL/2.0/.
+
+calendar-title = Calendr
+calendar-title-reminder = Atgoffwyr
+calendar-title-notification = Hysbysiadau
+calendar-title-category = Categorïau
+dateformat-label =
+    .value = Fformat Testun Dyddiad:
+    .accesskey = F
+#   $date (String) - the formatted example date
+dateformat-long =
+    .label = Hir: { $date }
+#   $date (String) - the formatted example date
+dateformat-short =
+    .label = Byr: { $date }
+use-system-timezone-radio-button =
+    .label = Defnyddio cylch amser y system
+set-timezone-manually-radio-button =
+    .label = Gosod y cylch amser â llaw
+timezone-label =
+    .value = Cylch Amser:
+weekstart-label =
+    .value = Cychwyn yr wythnos ar:
+    .accesskey = C
+day-1-name =
+    .label = Dydd Sul
+day-2-name =
+    .label = Dydd Llun
+day-3-name =
+    .label = Dydd Mawrth
+day-4-name =
+    .label = Dydd Mercher
+day-5-name =
+    .label = Dydd Iau
+day-6-name =
+    .label = Dydd Gwener
+day-7-name =
+    .label = Dydd Sadwrn
+show-weeknumber-label =
+    .label = Dangos rhif wythnos mewn golygon a misoedd bach
+    .accesskey = r
+workdays-label =
+    .value = Diwrnodau wythnos gwaith:
+day-1-checkbox =
+    .label = Sul
+    .accesskey = S
+day-2-checkbox =
+    .label = Llu
+    .accesskey = L
+day-3-checkbox =
+    .label = Maw
+    .accesskey = M
+day-4-checkbox =
+    .label = Mer
+    .accesskey = e
+day-5-checkbox =
+    .label = Iau
+    .accesskey = I
+day-6-checkbox =
+    .label = Gwe
+    .accesskey = G
+day-7-checkbox =
+    .label = Sad
+    .accesskey = a
+dayweek-legend = Golwg Diwrnod ac Wythnos
+visible-hours-label =
+    .value = Dangos:
+    .accesskey = a
+visible-hours-end-label =
+    .value = awr ar y tro
+day-start-label =
+    .value = Diwrnod yn cychwyn:
+    .accesskey = D
+day-end-label =
+    .value = Diwrnod yn gorffen:
+    .accesskey = i
+midnight-label =
+    .label = Canol Nos
+noon-label =
+    .label = Canol Dydd
+location-checkbox =
+    .label = Dangos y lleoliad
+    .accesskey = L
+multiweek-legend = Golwg Wythnosau
+number-of-weeks-label =
+    .value = Y nifer o wythnosau i'w dangos (gan gynnwys yr wythnos flaenorol):
+    .accesskey = n
+week-0-label =
+    .label = dim
+week-1-label =
+    .label = 1 wythnos
+week-2-label =
+    .label = 2 wythnos
+week-3-label =
+    .label = 3 wythnos
+week-4-label =
+    .label = 4 wythnos
+week-5-label =
+    .label = 5 wythnos
+week-6-label =
+    .label = 6 wythnos
+previous-weeks-label =
+    .value = Dangos yr wythnos flaenorol:
+    .accesskey = f
+todaypane-legend = Paen Heddiw
+agenda-days =
+    .value = Mae'r agenda'n dangos:
+    .accesskey = g
+event-task-legend = Digwyddiadau a Thasgau
+default-length-label =
+    .value = Hyd Digwyddiad a Thasg Rhagosodedig:
+    .accesskey = D
+task-start-label =
+    .value = Dyddiad Cychwyn:
+task-start-1-label =
+    .label = Dim
+task-start-2-label =
+    .label = Cychwyn y Diwrnod
+task-start-3-label =
+    .label = Diwedd y Dydd
+task-start-4-label =
+    .label = Yfory
+task-start-5-label =
+    .label = Wythnos Nesaf
+task-start-6-label =
+    .label = Cymharol â'r Amser Cyfredol
+task-start-7-label =
+    .label = Cymharol â'r Cychwyn
+task-start-8-label =
+    .label = Cymharol â'r Awr Nesaf
+task-due-label =
+    .value = Dyddiad Gorffen:
+edit-intab-label =
+    .label = Golygu digwyddiadau a thasgau mewn tab yn lle mewn ffenestr deialog.
+    .accesskey = G
+prompt-delete-label =
+    .label = Gofyn cyn dileu digwyddiadau a thasgau
+    .accesskey = G
+accessibility-legend = Hygyrchedd
+accessibility-colors-label =
+    .label = Mireinio lliwiau ar gyfer hygyrchedd
+    .accesskey = M
+reminder-legend = Pan fydd Disgwyl Atgoffwr:
+reminder-play-checkbox =
+    .label = Canu nodyn
+    .accesskey = n
+reminder-play-alarm-button =
+    .label = Chwarae
+    .accesskey = C
+reminder-default-sound-label =
+    .label = Defnyddio'r sain rhagosodedig
+    .accesskey = s
+reminder-custom-sound-label =
+    .label = Defnyddio'r ffeil sain ganlynol
+    .accesskey = D
+reminder-browse-sound-label =
+    .label = Pori…
+    .accesskey = P
+reminder-dialog-label =
+    .label = Dangos y ddeialog atgoffa
+    .accesskey = d
+missed-reminder-label =
+    .label = Dangos atgoffwyr wedi'u colli ar gyfer calendrau ysgrifenadwy
+    .accesskey = n
+reminder-default-legend = Rhagosodiadau Atgoffwyr
+default-snooze-label =
+    .value = Hyd Cysgu Rhagosodedig:
+    .accesskey = C
+event-alarm-label =
+    .value = Gosodiadau atgoffa rhagosodedig ar gyfer digwyddiadau:
+    .accesskey = G
+alarm-on-label =
+    .label = Ymlaen
+alarm-off-label =
+    .label = Diffodd
+task-alarm-label =
+    .value = Gosodiadau atgoffa rhagosodedig ar gyfer tasgau:
+    .accesskey = o
+event-alarm-time-label =
+    .value = Amser rhagosodedig y bydd atgoffwr yn cael ei bennu cyn digwyddiad:
+    .accesskey = A
+task-alarm-time-label =
+    .value = Amser rhagosodedig y bydd atgoffwr yn cael ei bennu cyn tasg:
+    .accesskey = m
+calendar-notifications-customize-label = Mae modd addasu hysbysiadau ar gyfer pob calendr yn ffenestr priodweddau'r calendr.
+category-new-label = Categori Newydd
+category-edit-label = Golygu Categori
+category-overwrite-title = Rhybudd: Enw dyblyg
+category-overwrite = Mae categori o'r enw yna yn bodoli eisoes. Hoffech chi ysgrifennu trosto?
+category-blank-warning = Rhaid rhoi enw categori.
diff --git a/thunderbird-l10n/cy/localization/cy/chat/matrix.ftl b/thunderbird-l10n/cy/localization/cy/chat/matrix.ftl
new file mode 100644
index 0000000000..c6534e34d6
--- /dev/null
+++ b/thunderbird-l10n/cy/localization/cy/chat/matrix.ftl
@@ -0,0 +1,41 @@
+# This Source Code Form is subject to the terms of the Mozilla Public
+# License, v. 2.0. If a copy of the MPL was not distributed with this
+# file, You can obtain one at http://mozilla.org/MPL/2.0/.
+
+
+### Matrix Protocol strings
+
+
+## Conversation names when a room has no user readable name.
+
+room-name-empty = Sgwrs wag
+# Variables:
+#  $oldName (String) - The previous name the conversation had before it was
+#    removed.
+room-name-empty-had-name = Sgwrs wag (oedd yn { $oldName } )
+# Variables:
+#  $participant (String) - The name of one participant that isn't the user.
+#  $otherParticipantsCount (Number) - The count of other participants apart from
+#    the user and $participant.
+room-name-others =
+    { $otherParticipantsCount ->
+        [zero] { $participant } a { $otherParticipantCount } arall
+        [one] { $participant } a { $otherParticipantCount } arall
+        [two] { $participant } a { $otherParticipantCount } arall
+        [few] { $participant } a { $otherParticipantCount } arall
+        [many] { $participant } a { $otherParticipantCount } arall
+       *[other] { $participant } a { $otherParticipantCount } arall
+    }
+# Variables:
+#  $participant (String) - The name of one participant that isn't the user.
+#  $otherParticipantCount (Number) - The count of other participants apart from
+#    the user and $participant.
+room-name-others2 =
+    { $otherParticipantCount ->
+        [zero] { $participant } a { $otherParticipantCount } arall
+        [one] { $participant } a { $otherParticipantCount } arall
+        [two] { $participant } a { $otherParticipantCount } arall
+        [few] { $participant } a { $otherParticipantCount } arall
+        [many] { $participant } a { $otherParticipantCount } arall
+       *[other] { $participant } a { $otherParticipantCount } arall
+    }
diff --git a/thunderbird-l10n/cy/localization/cy/crashreporter/aboutcrashes.ftl b/thunderbird-l10n/cy/localization/cy/crashreporter/aboutcrashes.ftl
new file mode 100644
index 0000000000..1cc78a899b
--- /dev/null
+++ b/thunderbird-l10n/cy/localization/cy/crashreporter/aboutcrashes.ftl
@@ -0,0 +1,31 @@
+# This Source Code Form is subject to the terms of the Mozilla Public
+# License, v- 2-0- If a copy of the MPL was not distributed with this
+# file, You can obtain one at http://mozilla-org/MPL/2-0/-
+
+
+# This Source Code Form is subject to the terms of the Mozilla Public
+# License, v. 2.0. If a copy of the MPL was not distributed with this
+# file, You can obtain one at http://mozilla.org/MPL/2.0/.
+
+crash-reports-title = Adroddiadau Chwalu
+
+submit-all-button-label = Cyflwyno Popeth
+delete-button-label = Clirio Popeth
+delete-confirm-title = Ydych chi'n siŵr?
+delete-unsubmitted-description = Bydd hyn yn dileu pob adroddiad chwalu heb eu cyflwyno ac nid oes modd ei ddadwneud.
+delete-submitted-description = Bydd hyn yn dileu'r rhestr o adroddiadau chwalu sydd wedi eu cyflwyno ond ni bydd yn dileu'r data sydd wedi ei gyflwyno. Nid oes modd dadwneud hyn.
+
+crashes-unsubmitted-label = Adroddiadau Chwalu heb eu Cyflwyno
+id-heading = Enw'r Adroddiad
+date-crashed-heading = Dyddiad y Chwalu
+submit-crash-button-label = Cyflwyno
+# This text is used to replace the label of the crash submit button
+# if the crash submission fails.
+submit-crash-button-failure-label = Methiant
+
+crashes-submitted-label = Adroddiadau Chwalu
+date-submitted-heading = Dyddiad Cyflwynwyd
+view-crash-button-label = Golwg
+
+no-reports-label = Does dim adroddiadau chwalu wedi eu cyflwyno.
+no-config-label = Mae'r rhaglen wedi ei ffurfweddu i ddangos adroddiadau chwalu. Rhaid gosod y <code>breakpad.reportURL</code>.
diff --git a/thunderbird-l10n/cy/localization/cy/devtools/client/aboutdebugging.ftl b/thunderbird-l10n/cy/localization/cy/devtools/client/aboutdebugging.ftl
new file mode 100644
index 0000000000..ff66abec52
--- /dev/null
+++ b/thunderbird-l10n/cy/localization/cy/devtools/client/aboutdebugging.ftl
@@ -0,0 +1,334 @@
+# This Source Code Form is subject to the terms of the Mozilla Public
+# License, v. 2.0. If a copy of the MPL was not distributed with this
+# file, You can obtain one at http://mozilla.org/MPL/2.0/.
+
+
+### These strings are used inside the about:debugging UI.
+
+
+# Page Title strings
+
+# Page title (ie tab title) for the Setup page
+about-debugging-page-title-setup-page = Dadfygio - Gosod
+# Page title (ie tab title) for the Runtime page
+# Variables:
+#   $selectedRuntimeId - ID of the current runtime, such as "this-firefox", "localhost:6080", etc.
+about-debugging-page-title-runtime-page = Dadfygio - Amser Rhedeg/ { $selectedRuntimeId }
+
+# Sidebar strings
+
+# Display name of the runtime for the currently running instance of Firefox. Used in the
+# Sidebar and in the Setup page.
+about-debugging-this-firefox-runtime-name = Y { -brand-shorter-name } hwn
+# Sidebar heading for selecting the currently running instance of Firefox
+# .name is processed by fluent-react / SidebarFixedItem
+about-debugging-sidebar-this-firefox =
+    .name = { about-debugging-this-firefox-runtime-name }
+# Sidebar heading for connecting to some remote source
+# .name is processed by fluent-react / SidebarFixedItem
+about-debugging-sidebar-setup =
+    .name = Gosod
+# Text displayed in the about:debugging sidebar when USB devices discovery is enabled.
+about-debugging-sidebar-usb-enabled = USB wedi'i alluogi
+# Text displayed in the about:debugging sidebar when USB devices discovery is disabled
+# (for instance because the mandatory ADB extension is not installed).
+about-debugging-sidebar-usb-disabled = USB wedi ei analluogi
+# Connection status (connected) for runtime items in the sidebar
+aboutdebugging-sidebar-runtime-connection-status-connected = Cysylltwyd
+# Connection status (disconnected) for runtime items in the sidebar
+aboutdebugging-sidebar-runtime-connection-status-disconnected = Datgysylltwyd
+# Text displayed in the about:debugging sidebar when no device was found.
+about-debugging-sidebar-no-devices = Heb ddarganfod unrhyw ddyfeisiau
+# Text displayed in buttons found in sidebar items representing remote runtimes.
+# Clicking on the button will attempt to connect to the runtime.
+about-debugging-sidebar-item-connect-button = Cysylltu
+# Text displayed in buttons found in sidebar items when the runtime is connecting.
+about-debugging-sidebar-item-connect-button-connecting = Cysylltu…
+# Text displayed in buttons found in sidebar items when the connection failed.
+about-debugging-sidebar-item-connect-button-connection-failed = Methodd y cysylltiad
+# Text displayed in connection warning on sidebar item of the runtime when connecting to
+# the runtime is taking too much time.
+about-debugging-sidebar-item-connect-button-connection-not-responding = Cysylltiad yn yr arfaeth o hyd, gwiriwch am negeseuon ar y porwr targed
+# Text displayed as connection error in sidebar item when the connection has timed out.
+about-debugging-sidebar-item-connect-button-connection-timeout = Cysylltiad wedi dod i ben
+# Text displayed in sidebar items for remote devices where a compatible browser (eg
+# Firefox) has not been detected yet. Typically, Android phones connected via USB with
+# USB debugging enabled, but where Firefox is not started.
+about-debugging-sidebar-runtime-item-waiting-for-browser = Aros am borwr...
+# Text displayed in sidebar items for remote devices that have been disconnected from the
+# computer.
+about-debugging-sidebar-runtime-item-unplugged = Wedi'i ddatgysylltu
+# Title for runtime sidebar items that are related to a specific device (USB, WiFi).
+# Variables:
+#   $displayName (string) - Displayed name
+#   $deviceName (string) - Name of the device
+about-debugging-sidebar-runtime-item-name =
+    .title = { $displayName } ({ $deviceName })
+# Title for runtime sidebar items where we cannot get device information (network
+# locations).
+# Variables:
+#   $displayName (string) - Displayed name
+about-debugging-sidebar-runtime-item-name-no-device =
+    .title = { $displayName }
+# Text to show in the footer of the sidebar that links to a help page
+# (currently: https://firefox-source-docs.mozilla.org/devtools-user/about_colon_debugging/)
+about-debugging-sidebar-support = Cefnogaeth dadfygio
+# Text to show as the ALT attribute of a help icon that accompanies the help about
+# debugging link in the footer of the sidebar
+about-debugging-sidebar-support-icon =
+    .alt = Eicon Cymorth
+# Text displayed in a sidebar button to refresh the list of USB devices. Clicking on it
+# will attempt to update the list of devices displayed in the sidebar.
+about-debugging-refresh-usb-devices-button = Adnewyddu dyfeisiau
+
+# Setup Page strings
+
+# Title of the Setup page.
+about-debugging-setup-title = Gosod
+# Introduction text in the Setup page to explain how to configure remote debugging.
+about-debugging-setup-intro = Ffurfweddwch y dull cysylltu rydych chi eisiau dadfygio eich dyfais o bell gydag ef.
+# Explanatory text in the Setup page about what the 'This Firefox' page is for
+about-debugging-setup-this-firefox2 = Defnyddiwch <a>{ about-debugging-this-firefox-runtime-name }</a> i ddadfygio tabiau, estyniadau a gweithwyr gwasanaeth ar y fersiwn hon o { -brand-shorter-name }.
+# Title of the heading Connect section of the Setup page.
+about-debugging-setup-connect-heading = Cysylltu Dyfais
+# USB section of the Setup page
+about-debugging-setup-usb-title = USB
+# Explanatory text displayed in the Setup page when USB debugging is disabled
+about-debugging-setup-usb-disabled = Bydd galluogi hyn yn llwytho i lawr ac yn ychwanegu'r cydrannau dadfygio Android USB at { -brand-shorter-name }.
+# Text of the button displayed in the USB section of the setup page when USB debugging is disabled.
+# Clicking on it will download components needed to debug USB Devices remotely.
+about-debugging-setup-usb-enable-button = Galluogi Dyfeisiau USB
+# Text of the button displayed in the USB section of the setup page when USB debugging is enabled.
+about-debugging-setup-usb-disable-button = Analluogi Dyfeisiau USB
+# Text of the button displayed in the USB section of the setup page while USB debugging
+# components are downloaded and installed.
+about-debugging-setup-usb-updating-button = Diweddaru…
+# USB section of the Setup page (USB status)
+about-debugging-setup-usb-status-enabled = Galluogwyd
+about-debugging-setup-usb-status-disabled = Analluogwyd
+about-debugging-setup-usb-status-updating = Diweddaru…
+# USB section step by step guide
+about-debugging-setup-usb-step-enable-dev-menu2 = Galluogi dewislen datblygwyr ar eich dyfais Android.
+# USB section step by step guide
+about-debugging-setup-usb-step-enable-debug2 = Galluogi Dadfygio USB yn Newislen Datblygwr Android.
+# USB section step by step guide
+about-debugging-setup-usb-step-enable-debug-firefox2 = Galluogi Dadfygio USB yn Firefox ar y ddyfais Android.
+# USB section step by step guide
+about-debugging-setup-usb-step-plug-device = Cysylltu'r ddyfais Android i'ch cyfrifiadur.
+# Text shown in the USB section of the setup page with a link to troubleshoot connection errors.
+# The link goes to https://firefox-source-docs.mozilla.org/devtools-user/about_colon_debugging/index.html#connecting-to-a-remote-device
+about-debugging-setup-usb-troubleshoot = Anhawster cysylltu â'r ddyfais USB? <a>Datrys problemau</a>
+# Network section of the Setup page
+about-debugging-setup-network =
+    .title = Lleoliad Rhwydwaith
+# Text shown in the Network section of the setup page with a link to troubleshoot connection errors.
+# The link goes to https://firefox-source-docs.mozilla.org/devtools-user/about_colon_debugging/index.html#connecting-over-the-network
+about-debugging-setup-network-troubleshoot = Anawsterau cysylltu drwy leoliad rhwydwaith? <a>Datrys problemau</a>
+# Text of a button displayed after the network locations "Host" input.
+# Clicking on it will add the new network location to the list.
+about-debugging-network-locations-add-button = Ychwanegu
+# Text to display when there are no locations to show.
+about-debugging-network-locations-empty-text = Nid oes unrhyw leoliadau rhwydwaith wedi'u hychwanegu eto.
+# Text of the label for the text input that allows users to add new network locations in
+# the Connect page. A host is a hostname and a port separated by a colon, as suggested by
+# the input's placeholder "localhost:6080".
+about-debugging-network-locations-host-input-label = Gwesteiwr
+# Text of a button displayed next to existing network locations in the Connect page.
+# Clicking on it removes the network location from the list.
+about-debugging-network-locations-remove-button = Tynnu
+# Text used as error message if the format of the input value was invalid in the network locations form of the Setup page.
+# Variables:
+#   $host-value (string) - The input value submitted by the user in the network locations form
+about-debugging-network-location-form-invalid = Gwestai annilys  “{ $host-value }”.Y fformat disgwyliedig yw “hostname:portnumber”.
+# Text used as error message if the input value was already registered in the network locations form of the Setup page.
+# Variables:
+#   $host-value (string) - The input value submitted by the user in the network locations form
+about-debugging-network-location-form-duplicate = Mae'r gwestai “{ $host-value }” eisoes wedi ei gofrestru
+
+# Runtime Page strings
+
+# Below are the titles for the various categories of debug targets that can be found
+# on "runtime" pages of about:debugging.
+# Title of the temporary extensions category (only available for "This Firefox" runtime).
+# .name is processed by fluent-react / DebugTargetPane
+about-debugging-runtime-temporary-extensions =
+    .name = Estyniadau Dros Dro
+# Title of the extensions category.
+# .name is processed by fluent-react / DebugTargetPane
+about-debugging-runtime-extensions =
+    .name = Estyniadau
+# Title of the tabs category.
+# .name is processed by fluent-react / DebugTargetPane
+about-debugging-runtime-tabs =
+    .name = Tabiau
+# Title of the service workers category.
+# .name is processed by fluent-react / DebugTargetPane
+about-debugging-runtime-service-workers =
+    .name = Gweithwyr Gwasanaeth
+# Title of the shared workers category.
+# .name is processed by fluent-react / DebugTargetPane
+about-debugging-runtime-shared-workers =
+    .name = Shared Workers
+# Title of the other workers category.
+# .name is processed by fluent-react / DebugTargetPane
+about-debugging-runtime-other-workers =
+    .name = Other Workers
+# Title of the processes category.
+# .name is processed by fluent-react / DebugTargetPane
+about-debugging-runtime-processes =
+    .name = Prosesau
+# Label of the button opening the performance profiler panel in runtime pages for remote
+# runtimes.
+about-debugging-runtime-profile-button2 = Perfformiad proffil
+# This string is displayed in the runtime page if the current configuration of the
+# target runtime is incompatible with service workers. "Learn more" points to:
+# https://firefox-source-docs.mozilla.org/devtools-user/about_colon_debugging/index.html#service-workers-not-compatible
+about-debugging-runtime-service-workers-not-compatible = Nid yw ffurfweddiad eich porwr yn cydweddu â Gweithwyr Gwasanaeth. <a>Darllen rhagor</a>
+# This string is displayed in the runtime page if the remote browser version is too old.
+# "Troubleshooting" link points to https://firefox-source-docs.mozilla.org/devtools-user/about_colon_debugging/
+# { $runtimeVersion } is the version of the remote browser (for instance "67.0a1")
+# { $minVersion } is the minimum version that is compatible with the current Firefox instance (same format)
+about-debugging-browser-version-too-old = Mae gan y porwr cysylltiedig hen fersiwn ({ $runtimeVersion }). Y fersiwn lleiaf sy'n cael ei gynnal yw ({ $minVersion }). Mae hwn yn osodiad sydd dim yn cael ei gynnal a gall achosi i DevTools fethu. Diweddarwch y porwr cysylltiedig. <a>Datrys problemau</a>
+# Dedicated message for a backward compatibility issue that occurs when connecting:
+# from Fx 70+ to the old Firefox for Android (aka Fennec) which uses Fx 68.
+about-debugging-browser-version-too-old-fennec = Nid oes modd i'r fersiwn yma o Firefox ddadfygio Firefox ar gyfer Android (68). Rydym yn argymell gosod Firefox ar gyfer Android Nightly ar eich ffôn i'w brofi. <a> Rhagor o fanylion </a>
+# This string is displayed in the runtime page if the remote browser version is too recent.
+# "Troubleshooting" link points to https://firefox-source-docs.mozilla.org/devtools-user/about_colon_debugging/
+# { $runtimeID } is the build ID of the remote browser (for instance "20181231", format is yyyyMMdd)
+# { $localID } is the build ID of the current Firefox instance (same format)
+# { $runtimeVersion } is the version of the remote browser (for instance "67.0a1")
+# { $localVersion } is the version of your current browser (same format)
+about-debugging-browser-version-too-recent = Mae'r porwr cysylltiedig yn fwy diweddar ( { $runtimeVersion }, buildID { $runtimeID }) na'ch { -brand-shorter-name } ({ $localVersion }, BuildID{ $localID }). Mae hwn yn osodiad heb gefnogaeth ac fe all beri i DevTools fethu. Diweddarwch Firefox. <a>Datrys Problemau</a>
+# Displayed for runtime info in runtime pages.
+# { $name } is brand name such as "Firefox Nightly"
+# { $version } is version such as "64.0a1"
+about-debugging-runtime-name = { $name } ({ $version })
+# Text of a button displayed in Runtime pages for remote runtimes.
+# Clicking on the button will close the connection to the runtime.
+about-debugging-runtime-disconnect-button = Datgysylltu
+# Text of the connection prompt button displayed in Runtime pages, when the preference
+# "devtools.debugger.prompt-connection" is false on the target runtime.
+about-debugging-connection-prompt-enable-button = Galluogi anogyn cysylltu
+# Text of the connection prompt button displayed in Runtime pages, when the preference
+# "devtools.debugger.prompt-connection" is true on the target runtime.
+about-debugging-connection-prompt-disable-button = Analluogi anogyn cysylltu
+# Title of a modal dialog displayed on remote runtime pages after clicking on the Profile Runtime button.
+about-debugging-profiler-dialog-title2 = Proffiliwr
+# Clicking on the header of a debug target category will expand or collapse the debug
+# target items in the category. This text is used as ’title’ attribute of the header,
+# to describe this feature.
+about-debugging-collapse-expand-debug-targets = Cau / ehangu
+
+# Debug Targets strings
+
+# Displayed in the categories of "runtime" pages that don't have any debug target to
+# show. Debug targets depend on the category (extensions, tabs, workers...).
+about-debugging-debug-target-list-empty = Dim byd eto.
+# Text of a button displayed next to debug targets of "runtime" pages. Clicking on this
+# button will open a DevTools toolbox that will allow inspecting the target.
+# A target can be an addon, a tab, a worker...
+about-debugging-debug-target-inspect-button = Archwilio
+# Text of a button displayed in the "This Firefox" page, in the Temporary Extension
+# section. Clicking on the button will open a file picker to load a temporary extension
+about-debugging-tmp-extension-install-button = Llwytho Ychwanegyn Dros Dro…
+# Text displayed when trying to install a temporary extension in the "This Firefox" page.
+about-debugging-tmp-extension-install-error = Digwyddodd gwall wrth osod ychwanegyn dros dro
+# Text of a button displayed for a temporary extension loaded in the "This Firefox" page.
+# Clicking on the button will reload the extension.
+about-debugging-tmp-extension-reload-button = Ail-lwytho
+# Text of a button displayed for a temporary extension loaded in the "This Firefox" page.
+# Clicking on the button will uninstall the extension and remove it from the page.
+about-debugging-tmp-extension-remove-button = Tynnu
+# Text of a button displayed for a temporary extension loaded in the "This Firefox" page.
+# Clicking on the button will forcefully terminate the extension background script (button
+# only visible in extensions that includes a non-persistent background script, either an
+# event page or a background service worker).
+about-debugging-tmp-extension-terminate-bgscript-button = Terfynu sgript cefndir
+# Message displayed in the file picker that opens to select a temporary extension to load
+# (triggered by the button using "about-debugging-tmp-extension-install-button")
+# manifest.json .xpi and .zip should not be localized.
+# Note: this message is only displayed in Windows and Linux platforms.
+about-debugging-tmp-extension-install-message = Dewis ffeil maniffest.json neu .xpi /.zip
+# This string is displayed as a message about the add-on having a temporaryID.
+about-debugging-tmp-extension-temporary-id = Mae gan y WebExtension ID dros dro. <a>Darllen rhagor</a>
+# Text displayed for extensions in "runtime" pages, before displaying a link the extension's
+# manifest URL.
+about-debugging-extension-manifest-url =
+    .label = URL Maniffest
+# Text displayed for extensions in "runtime" pages, before displaying the extension's uuid.
+# UUIDs look like b293e463-481e-5148-a487-5aaf7a130429
+about-debugging-extension-uuid =
+    .label = UUID mewnol
+# Text displayed for extensions (temporary extensions only) in "runtime" pages, before
+# displaying the location of the temporary extension.
+about-debugging-extension-location =
+    .label = Lleoliad
+# Text displayed for extensions in "runtime" pages, before displaying the extension's ID.
+# For instance "geckoprofiler@mozilla.com" or "{ed26ddcb-5611-4512-a89a-51b8db81cfb2}".
+about-debugging-extension-id =
+    .label = Enw'r Estyniadau
+# Text displayed for extensions in "runtime" pages, before displaying the status of the
+# extension background script.
+about-debugging-extension-backgroundscript =
+    .label = Sgript gefndir
+# Displayed for extension using a non-persistent background page (either an event page or
+# background service worker) when the background script is currently running.
+about-debugging-extension-backgroundscript-status-running = Yn rhedeg
+# Displayed for extension using a non-persistent background page when is currently stopped.
+about-debugging-extension-backgroundscript-status-stopped = Ataliawyd
+# This string is displayed as a label of the button that pushes a test payload
+# to a service worker.
+# Note this relates to the "Push" API, which is normally not localized so it is
+# probably better to not localize it.
+# .disabledTitle is processed by the fluent-react / ActionButton code.
+about-debugging-worker-action-push2 = Gwthio
+    .disabledTitle = Mae Gweithiwr Gwasanaeth gwthio wedi ei analluogi ar hyn o bryd ar gyfer amlbroses { -brand-shorter-name }
+# This string is displayed as a label of the button that starts a service worker.
+# .disabledTitle is processed by the fluent-react / ActionButton code.
+about-debugging-worker-action-start2 = Cychwyn
+    .disabledTitle = Mae Gweithiwr Gwasanaeth gwthio wedi ei analluogi ar hyn o bryd ar gyfer amlbroses { -brand-shorter-name }
+# This string is displayed as a label of the button that unregisters a service worker.
+about-debugging-worker-action-unregister = Dadgofrestru
+# Displayed for service workers in runtime pages that listen to Fetch events.
+about-debugging-worker-fetch-listening =
+    .label = Estyn
+    .value = Gwrando am ddigwyddiadau estyn
+# Displayed for service workers in runtime pages that do not listen to Fetch events.
+about-debugging-worker-fetch-not-listening =
+    .label = Estyn
+    .value = Ddim yn gwrando ar ddigwyddiadau estyn
+# Displayed for service workers in runtime pages that are currently running (service
+# worker instance is active).
+about-debugging-worker-status-running = Yn rhedeg
+# Displayed for service workers in runtime pages that are registered but stopped.
+about-debugging-worker-status-stopped = Ataliawyd
+# Displayed for service workers in runtime pages that are registering.
+about-debugging-worker-status-registering = Cofrestru
+# Displayed for service workers in runtime pages, to label the scope of a worker
+about-debugging-worker-scope =
+    .label = Cwmpas
+# Displayed for service workers in runtime pages, to label the push service endpoint (url)
+# of a worker
+about-debugging-worker-push-service =
+    .label = Gwasanaeth Gwthio
+# Displayed as title of the inspect button when service worker debugging is disabled.
+about-debugging-worker-inspect-action-disabled =
+    .title = Mae Gweithiwr Gwasanaeth gwthio wedi ei analluogi ar hyn o bryd ar gyfer amlbroses { -brand-shorter-name }
+# Displayed as title of the inspect button for zombie tabs (e.g. tabs loaded via a session restore).
+about-debugging-zombie-tab-inspect-action-disabled =
+    .title = Nid yw'r tab wedi'i lwytho'n llawn ac nid oes modd ei archwilio
+# Displayed as name for the Main Process debug target in the Processes category. Only for
+# remote runtimes, if `devtools.aboutdebugging.process-debugging` is true.
+about-debugging-multiprocess-toolbox-name = Blwch Offer Amlbroses
+# Displayed as description for the Main Process debug target in the Processes category.
+# Only for remote browsers, if `devtools.aboutdebugging.process-debugging` is true.
+about-debugging-multiprocess-toolbox-description = Prif Broses a Phrosesau Cynnwys ar gyfer y porwr targed
+# Alt text used for the close icon of message component (warnings, errors and notifications).
+about-debugging-message-close-icon =
+    .alt = Cau neges
+# Label text used for the error details of message component.
+about-debugging-message-details-label-error = Manylion gwall
+# Label text used for the warning details of message component.
+about-debugging-message-details-label-warning = Manylion rhybudd
+# Label text used for default state of details of message component.
+about-debugging-message-details-label = Manylion
diff --git a/thunderbird-l10n/cy/localization/cy/devtools/client/accessibility.ftl b/thunderbird-l10n/cy/localization/cy/devtools/client/accessibility.ftl
new file mode 100644
index 0000000000..f69f49fddc
--- /dev/null
+++ b/thunderbird-l10n/cy/localization/cy/devtools/client/accessibility.ftl
@@ -0,0 +1,72 @@
+# This Source Code Form is subject to the terms of the Mozilla Public
+# License, v. 2.0. If a copy of the MPL was not distributed with this
+# file, You can obtain one at http://mozilla.org/MPL/2.0/.
+
+
+### These strings are used inside the Accessibility panel.
+
+accessibility-learn-more = Darllen rhagor
+accessibility-text-label-header = Labeli ac Enwau Testun
+accessibility-keyboard-header = Bysellfwrdd
+
+## These strings are used in the overlay displayed when running an audit in the accessibility panel
+
+accessibility-progress-initializing = Cychwyn…
+    .aria-valuetext = Cychwyn…
+# This string is displayed in the audit progress bar in the accessibility panel.
+# Variables:
+#   $nodeCount (Integer) - The number of nodes for which the audit was run so far.
+accessibility-progress-progressbar =
+    { $nodeCount ->
+        [zero] Gwirio { $nodeCount } nod
+        [one] Gwirio { $nodeCount } nod
+        [two] Gwirio { $nodeCount } nod
+        [few] Gwirio { $nodeCount } nod
+        [many] Gwirio { $nodeCount } nod
+       *[other] Gwirio { $nodeCount } nod
+    }
+accessibility-progress-finishing = Cwblhau…
+    .aria-valuetext = Cwblhau…
+
+## Text entries that are used as text alternative for icons that depict accessibility issues.
+
+accessibility-warning =
+    .alt = Rhybudd
+accessibility-fail =
+    .alt = Gwall
+accessibility-best-practices =
+    .alt = Ymarfer Gorau
+
+## Text entries for a paragraph used in the accessibility panel sidebar's checks section
+## that describe that currently selected accessible object has an accessibility issue
+## with its text label or accessible name.
+
+accessibility-text-label-issue-area = Defnyddiwch briodoledd <code>alt</code> i labelu elfennau <div>ardal</div> sydd â phriodoledd <span>href</span>. <a>Darllen rhagor</a>
+accessibility-text-label-issue-dialog = Rhaid labelu deialogau. <a>Darllen rhagor</a>
+accessibility-text-label-issue-document-title = Rhaid i ddogfennau feddu ar <code>deitl</code>. <a>Darllen rhagor</a>
+accessibility-text-label-issue-embed = Rhaid labelu cynnwys wedi'i fewnblannu. <a>Darllen rhagor</a>
+accessibility-text-label-issue-figure = Dylid labelu nodau â chapsiynau dewisol. <a>Darllen rhagor</a>
+accessibility-text-label-issue-fieldset = Rhaid labelu elfennau <code>fieldset</code>. <a>Darllen rhagor</a>
+accessibility-text-label-issue-fieldset-legend2 = Defnyddiwch elfen <code>legend</code> i labelu <span>fieldset</span>. <a>Darllen rhagor</a>
+accessibility-text-label-issue-form = Rhaid labelu elfennau ffurflen. <a>Darllen rhagor</a>
+accessibility-text-label-issue-form-visible = Dylai fod gan elfennau ffurflenni label testun gweladwy. <a>Darllen rhagor</a>
+accessibility-text-label-issue-frame = Rhaid labelu elfennau <code>frame</code>. <a>Darllen rhagor</a>
+accessibility-text-label-issue-glyph = Defnyddiwch briodoledd <code>alt</code> i labelu elfennau <span>mglyph</span>. <a>Darllen rhagor</a>
+accessibility-text-label-issue-heading = Rhaid labelu'r penawdau. <a>Darllen rhagor</a>
+accessibility-text-label-issue-heading-content = Dylai penawdau gynnwys testun gweladwy. <a>Darllen rhagor</a>
+accessibility-text-label-issue-iframe = Defnyddiwch briodoledd <code>title</code> i ddisgrifio cynnwys <span>iframe</span>. <a>Darllen rhagor</a>
+accessibility-text-label-issue-image = Rhaid labelu cynnwys gyda delweddau. <a>Darllen rhagor</a>
+accessibility-text-label-issue-interactive = Rhaid labelu elfennau rhyngweithiol. <a>Darllen rhagor</a>
+accessibility-text-label-issue-optgroup-label2 = Defnyddiwch briodoledd <code>label</code> i labelu <span>optgroup</span>. <a>Darllen rhagor</a>
+accessibility-text-label-issue-toolbar = Rhaid labelu bariau offer pan fydd mwy nag un bar offer. <a>Darllen rhagor</a>
+
+## Text entries for a paragraph used in the accessibility panel sidebar's checks section
+## that describe that currently selected accessible object has a keyboard accessibility
+## issue.
+
+accessibility-keyboard-issue-semantics = Dylai elfennau ffocwsadwy fod â semanteg ryngweithiol. <a>Darllen rhagor</a>
+accessibility-keyboard-issue-tabindex = Ceisiwch osgoi defnyddio priodoledd <code>tabindex</code> sy'n fwy na sero. <a>Darllen rhagor</a>
+accessibility-keyboard-issue-action = Rhaid gallu actifadu elfennau rhyngweithiol gan ddefnyddio bysellfwrdd. <a>Darllen rhagor</a>
+accessibility-keyboard-issue-focusable = Rhaid i elfennau rhyngweithiol fod yn ffocwsadwy. <a>Darllen rhagor</a>
+accessibility-keyboard-issue-focus-visible = Efallai bod elfen ffocwsadwy yn brin o steilio ffocws. <a>Darllen rhagor</a>
+accessibility-keyboard-issue-mouse-only = Dylai elfennau clicadwy fod â semanteg ryngweithiol. <a>Darllen rhagor</a>
diff --git a/thunderbird-l10n/cy/localization/cy/devtools/client/application.ftl b/thunderbird-l10n/cy/localization/cy/devtools/client/application.ftl
new file mode 100644
index 0000000000..7288dcb54a
--- /dev/null
+++ b/thunderbird-l10n/cy/localization/cy/devtools/client/application.ftl
@@ -0,0 +1,121 @@
+# This Source Code Form is subject to the terms of the Mozilla Public
+# License, v. 2.0. If a copy of the MPL was not distributed with this
+# file, You can obtain one at http://mozilla.org/MPL/2.0/.
+
+
+### These strings are used inside the Application panel which is available
+### by setting the preference `devtools-application-enabled` to true.
+
+
+### The correct localization of this file might be to keep it in English, or another
+### language commonly spoken among web developers. You want to make that choice consistent
+### across the developer tools. A good criteria is the language in which you'd find the
+### best documentation on web development on the web.
+
+# Header for the list of Service Workers displayed in the application panel for the current page.
+serviceworker-list-header = Gweithwyr Gwasanaeth
+# Text displayed next to the list of Service Workers to encourage users to check out
+# about:debugging to see all registered Service Workers.
+serviceworker-list-aboutdebugging = Agor <a>about:debugging</a> ar gyfer Gweithwyr Gwasanaeth o barthau eraill
+# Text for the button to unregister a Service Worker. Displayed for active Service Workers.
+serviceworker-worker-unregister = Dadgofrestru
+# Text for the debug link displayed for an already started Service Worker. Clicking on the
+# link opens a new devtools toolbox for this service worker. The title attribute is only
+# displayed when the link is disabled.
+serviceworker-worker-debug = Dadfygio
+    .title = Dim ond gweithwyr gwasanaeth sy'n rhedeg y mae modd eu dadfygio
+# Alt text for the image icon displayed inside a debug link for a service worker.
+serviceworker-worker-inspect-icon =
+    .alt = Archwilio
+# Text for the start link displayed for a registered but not running Service Worker.
+# Clicking on the link will attempt to start the service worker.
+serviceworker-worker-start3 = Cychwyn
+# Text displayed for the updated time of the service worker. The <time> element will
+# display the last update time of the service worker script.
+# Variables:
+#   $date (date) - Update date
+serviceworker-worker-updated = Diweddarwyd <time>{ DATETIME($date, month: "long", year: "numeric", day: "numeric", hour: "numeric", minute: "numeric", second: "numeric") }</time>
+
+## Service Worker status strings: all serviceworker-worker-status-* strings are also
+## defined in aboutdebugging.properties and should be synchronized with them.
+
+# Service Worker status. A running service worker is registered, currently executed, can
+# be debugged and stopped.
+serviceworker-worker-status-running = Yn rhedeg
+# Service Worker status. A stopped service worker is registered but not currently active.
+serviceworker-worker-status-stopped = Ataliawyd
+# Text displayed when no service workers are visible for the current page.
+serviceworker-empty-intro2 = Heb ganfod unrhyw weithwyr gwasanaeth
+# Link will open https://developer.mozilla.org/docs/Web/API/Service_Worker_API/Using_Service_Workers
+serviceworker-empty-intro-link = Darllen rhagor
+# Text displayed when there are no Service Workers to display for the current page,
+# introducing hints to debug Service Worker issues.
+# <a> and <span> are links that will open the webconsole and the debugger, respectively.
+serviceworker-empty-suggestions2 = Os dylai'r gweithiwr cyfredol fod â gweithiwr gwasanaeth, fe allech chi chwilio am wallau yn y <a>Consol</a> neu gamu trwy'ch cofrestriad gweithiwr gwasanaeth yn y <span>Dadfygiwr</span>.
+# Suggestion to go to about:debugging in order to see Service Workers for all domains.
+# Link will open about:debugging in a new tab.
+serviceworker-empty-suggestions-aboutdebugging2 = Gweld gweithwyr gwasanaeth o barthau eraill
+# Header for the Manifest page when we have an actual manifest
+manifest-view-header = Maniffest Ap
+# Header for the Manifest page when there's no manifest to inspect
+manifest-empty-intro2 = Heb ganfod maniffesto ap gwe
+# The link will open https://developer.mozilla.org/en-US/docs/Web/Manifest
+manifest-empty-intro-link = Dysgwch sut i ychwanegu maniffest
+# Header for the Errors and Warnings section of Manifest inspection displayed in the application panel.
+manifest-item-warnings = Gwallau a Rhybuddion
+# Header for the Identity section of Manifest inspection displayed in the application panel.
+manifest-item-identity = Hunaniaeth
+# Header for the Presentation section of Manifest inspection displayed in the application panel.
+manifest-item-presentation = Cyflwyniad
+# Header for the Icon section of Manifest inspection displayed in the application panel.
+manifest-item-icons = Eiconau
+# Text displayed while we are loading the manifest file
+manifest-loading = Llwytho maniffest ...
+# Text displayed when the manifest has been successfully loaded
+manifest-loaded-ok = Manifest wedi'i lwytho.
+# Text displayed as a caption when there has been an error while trying to
+# load the manifest
+manifest-loaded-error = Bu gwall wrth lwytho'r maniffest:
+# Text displayed as an error when there has been a Firefox DevTools error while
+# trying to load the manifest
+manifest-loaded-devtools-error = Gwall Firefox DevTools
+# Text displayed when the page has no manifest available
+manifest-non-existing = Heb ganfod maniffest i'w arolygu
+# Text displayed when the page has a manifest embedded in a Data URL and
+# thus we cannot link to it.
+manifest-json-link-data-url = Mae'r maniffest wedi'i fewnosod mewn URL Data.
+# Text displayed at manifest icons to label their purpose, as declared
+# in the manifest.
+# Variables:
+#   $purpose (string) - Manifest purpose
+manifest-icon-purpose = Pwrpas: <code>{ $purpose }</code>
+# Text displayed as the alt attribute for <img> tags showing the icons in the
+# manifest.
+manifest-icon-img =
+    .alt = Eicon
+# Text displayed as the title attribute for <img> tags showing the icons in the
+# manifest.
+# Variables:
+#   $sizes (string) - User-dependent string that has been parsed as a
+#                     space-separated list of `<width>x<height>` sizes or
+#                     the keyword `any`.
+manifest-icon-img-title = Eicon gyda meintiau: { $sizes }
+# Text displayed as the title attribute for <img> tags showing the icons in the
+# manifest, in case there's no icon size specified by the user
+manifest-icon-img-title-no-sizes = Eicon maint amhenodol
+# Sidebar navigation item for Manifest sidebar item section
+sidebar-item-manifest = Maniffest
+    .alt = Eicon Maniffest
+    .title = Maniffest
+# Sidebar navigation item for Service Workers sidebar item section
+sidebar-item-service-workers = Gweithwyr Gwasanaeth
+    .alt = Eicon Gweithwyr Gwasanaeth
+    .title = Gweithwyr Gwasanaeth
+# Text for the ALT and TITLE attributes of the warning icon
+icon-warning =
+    .alt = Eicon rhybuddio
+    .title = Rhybudd
+# Text for the ALT and TITLE attributes of the error icon
+icon-error =
+    .alt = Eicon gwall
+    .title = Gwall
diff --git a/thunderbird-l10n/cy/localization/cy/devtools/client/compatibility.ftl b/thunderbird-l10n/cy/localization/cy/devtools/client/compatibility.ftl
new file mode 100644
index 0000000000..a969bfa42b
--- /dev/null
+++ b/thunderbird-l10n/cy/localization/cy/devtools/client/compatibility.ftl
@@ -0,0 +1,58 @@
+# This Source Code Form is subject to the terms of the Mozilla Public
+# License, v. 2.0. If a copy of the MPL was not distributed with this
+# file, You can obtain one at http://mozilla.org/MPL/2.0/.
+
+
+## Messages used as headers in the main pane
+
+compatibility-selected-element-header = Elfennau Dewiswyd
+compatibility-all-elements-header = Pob Mater
+
+## Message used as labels for the type of issue
+
+compatibility-issue-deprecated = (anghymeradwy)
+compatibility-issue-experimental = (arbrofol)
+compatibility-issue-prefixneeded = (angen rhagddodiad)
+compatibility-issue-deprecated-experimental = (anghymeradwy, arbrofol)
+compatibility-issue-deprecated-prefixneeded = (anghymeradwy, angen rhagddodiad)
+compatibility-issue-experimental-prefixneeded = (arbrofol, angen rhagddodiad)
+compatibility-issue-deprecated-experimental-prefixneeded = anghymeradwy, arbrofol, angen rhagddodiad)
+
+## Messages used as labels and titles for buttons in the footer
+
+compatibility-settings-button-label = Gosodiadau
+compatibility-settings-button-title =
+    .title = Gosodiadau
+
+## Messages used as headers in settings pane
+
+compatibility-settings-header = Gosodiadau
+compatibility-target-browsers-header = Porwyr Targed
+
+##
+
+# Text used as the label for the number of nodes where the issue occurred
+# Variables:
+#   $number (Number) - The number of nodes where the issue occurred
+compatibility-issue-occurrences =
+    { $number ->
+        [zero] { $number } digwyddiad
+        [one] { $number } digwyddiad
+        [two] { $number } digwyddiad
+        [few] { $number } digwyddiad
+        [many] { $number } digwyddiad
+       *[other] { $number } digwyddiad
+    }
+
+compatibility-no-issues-found = Dim materion cydnawsedd. wedi'u canfod.
+compatibility-close-settings-button =
+    .title = Cau'r gosodiadau
+
+# Text used in the element containing the browser icons for a given compatibility issue.
+# Line breaks are significant.
+# Variables:
+#   $browsers (String) - A line-separated list of browser information (e.g. Firefox 98\nChrome 99).
+compatibility-issue-browsers-list =
+    .title =
+        Materion cydnawsedd yn:
+        { $browsers }
diff --git a/thunderbird-l10n/cy/localization/cy/devtools/client/perftools.ftl b/thunderbird-l10n/cy/localization/cy/devtools/client/perftools.ftl
new file mode 100644
index 0000000000..608f6ac820
--- /dev/null
+++ b/thunderbird-l10n/cy/localization/cy/devtools/client/perftools.ftl
@@ -0,0 +1,163 @@
+# This Source Code Form is subject to the terms of the Mozilla Public
+# License, v. 2.0. If a copy of the MPL was not distributed with this
+# file, You can obtain one at http://mozilla.org/MPL/2.0/.
+
+
+### These strings are used in DevTools’ performance-new panel, about:profiling, and
+### the remote profiling panel. There are additional profiler strings in the appmenu.ftl
+### file that are used for the profiler popup.
+
+perftools-intro-title = Gosodiadau'r Proffiliwr
+perftools-intro-description =
+    Mae'r cofnodion yn cychwyn profiler.firefox.com mewn tab newydd. Mae'r holl ddata yn cael ei storio
+    yn lleol, ond gallwch ddewis ei lwytho i'w rannu.
+
+## All of the headings for the various sections.
+
+perftools-heading-settings = Gosodiadau Llawn
+perftools-heading-buffer = Gosodiadau'r Byffer
+perftools-heading-features = Nodweddion
+perftools-heading-features-default = Nodweddion (Ymlaen yn rhagosodedig drwy argymhelliad)
+perftools-heading-features-disabled = Nodweddion wedi'u Hanalluogi
+perftools-heading-features-experimental = Arbrofol
+perftools-heading-threads = Edafedd
+perftools-heading-threads-jvm = Trywyddau JVM
+perftools-heading-local-build = Adeiladedd lleol
+
+##
+
+perftools-description-intro =
+    Mae'r cofnodion yn cychwyn <a>profiler.firefox.com</a> mewn tab newydd. Mae'r holl ddata yn cael ei storio
+    yn lleol, ond gallwch ddewis ei lwytho i'w rannu.
+perftools-description-local-build =
+    Os ydych chi'n proffilio adeiladedd rydych wedi’i lunio'ch hun, ar y 
+    peiriant hwn,
+    ychwanegwch objdir eich adeiladedd at y rhestr isod fel bod
+    modd ei ddefnyddio i chwilio am fanylion symbolau.
+
+## The controls for the interval at which the profiler samples the code.
+
+perftools-range-interval-label = Cyfnod samplu:
+perftools-range-interval-milliseconds = { NUMBER($interval, maxFractionalUnits: 2) } ms
+
+##
+
+# The size of the memory buffer used to store things in the profiler.
+perftools-range-entries-label = Maint byffer:
+
+perftools-custom-threads-label = Ychwanegwch drywydd cyfaddas yn ôl enw:
+
+perftools-devtools-interval-label = Cyfnod:
+perftools-devtools-threads-label = Trywyddion:
+perftools-devtools-settings-label = Gosodiadau
+
+## Various statuses that affect the current state of profiling, not typically displayed.
+
+perftools-status-recording-stopped-by-another-tool = Cafodd y cofnodi ei atal gan offeryn arall.
+perftools-status-restart-required = Rhaid ailgychwyn y porwr i alluogi'r nodwedd hon.
+
+## These are shown briefly when the user is waiting for the profiler to respond.
+
+perftools-request-to-stop-profiler = Atal y cofnodi
+perftools-request-to-get-profile-and-stop-profiler = Cipio proffil
+
+##
+
+perftools-button-start-recording = Cychwyn cofnodi
+perftools-button-capture-recording = Cipio'r cofnod
+perftools-button-cancel-recording = Diddymu'r cofnodi
+perftools-button-save-settings = Cadw gosodiadau a mynd nôl
+perftools-button-restart = Ailgychwyn
+perftools-button-add-directory = Ychwanegwch gyfeiriadur
+perftools-button-remove-directory = Tynnwch y dewis
+perftools-button-edit-settings = Golygu Gosodiadau...
+
+## These messages are descriptions of the threads that can be enabled for the profiler.
+
+perftools-thread-gecko-main =
+    .title = Y prif brosesau ar gyfer y broses riant a phrosesau cynnwys
+perftools-thread-compositor =
+    .title = Cyfansoddion gyda'i gilydd gwahanol elfennau wedi'u paentio ar y dudalen
+perftools-thread-dom-worker =
+    .title = Dolen gweithwyr gwe a gweithwyr gwasanaeth
+perftools-thread-renderer =
+    .title = Pan fydd WebRender wedi'i alluogi, mae'r trywydd sy'n gweithredu OpenGL yn galw
+perftools-thread-render-backend =
+    .title = Trywydd WebRender RenderBackend
+perftools-thread-timer =
+    .title = Yr amseryddion trin trywydd (setTimeout, setInterval, nsITimer)
+perftools-thread-style-thread =
+    .title = Mae cyfrifiant arddull yn cael ei rannu i drywyddion lluosog
+pref-thread-stream-trans =
+    .title = Cludiant llif rhwydwaith
+perftools-thread-socket-thread =
+    .title = Y trywydd lle mae cod rhwydweithio yn rhedeg unrhyw alwadau rhwystro socedi
+perftools-thread-img-decoder =
+    .title = Trywyddion datgodio delwedd
+perftools-thread-dns-resolver =
+    .title = Mae datrysiad DNS yn digwydd ar y trywydd hwn
+perftools-thread-task-controller =
+    .title = Edafedd pwll edafedd TaskController
+perftools-thread-jvm-gecko =
+    .title = Prif drywydd Gecko JVM
+perftools-thread-jvm-nimbus =
+    .title = Y prif drywydd ar gyfer arbrofion Nimbus SDK
+perftools-thread-jvm-default-dispatcher =
+    .title = Yr anfonwr rhagosodedig ar gyfer llyfrgell coroutines Kotlin
+perftools-thread-jvm-glean =
+    .title = Y prif drywydd ar gyfer telemetreg Glean SDK
+perftools-thread-jvm-arch-disk-io =
+    .title = Anfonwr IO ar gyfer llyfrgell coroutines Kotlin
+perftools-thread-jvm-pool =
+    .title = Trywyddau wedi'u creu mewn cronfa trywyddau dienw
+
+##
+
+perftools-record-all-registered-threads = Osgoi'r dewisiadau uchod a chofnodi'r holl drywyddion cofrestredig
+
+perftools-tools-threads-input-label =
+    .title = Mae'r enwau trywyddion hyn yn rhestr sydd wedi'i gwahanu â choma sy'n cael ei ddefnyddio i alluogi proffilio trywydd yn y proffiliwr. Mae angen i'r enw fod yn cyfateb yn unig â'r enw trywydd i'w gynnwys. Mae'n sensitif i ofod gwyn.
+
+## Onboarding UI labels. These labels are displayed in the new performance panel UI, when
+## devtools.performance.new-panel-onboarding preference is true.
+
+perftools-onboarding-message = <b>Newydd</b>: Mae'r { -profiler-brand-name } bellach wedi'i integreiddio i Offer Datblygwr. <a>Gweld rhagor</a> am yr offeryn newydd pwerus hwn.
+
+perftools-onboarding-close-button =
+    .aria-label = Cau'r neges cyflwyno
+
+## Profiler presets
+
+
+# Presets and their l10n IDs are defined in the file
+# devtools/client/performance-new/popup/background.jsm.js
+# The same labels and descriptions are also defined in appmenu.ftl.
+
+
+# Presets and their l10n IDs are defined in the file
+# devtools/client/performance-new/shared/background.jsm.js
+# The same labels and descriptions are also defined in appmenu.ftl.
+
+perftools-presets-web-developer-label = Datblygwr Gwe
+perftools-presets-web-developer-description = Y rhagosodiad sy'n cael ei argymell ar gyfer y rhan fwyaf o ddadfygio apiau gwe, gyda gorbenion isel.
+
+perftools-presets-firefox-label = { -brand-shorter-name }
+perftools-presets-firefox-description = Y rhagosodiad a argymhellir ar gyfer proffilio { -brand-shorter-name }.
+
+perftools-presets-graphics-label = Graffigau
+perftools-presets-graphics-description = Y rhagosodiad ar gyfer ymchwilio i wallau graffeg yn { -brand-shorter-name }.
+
+perftools-presets-media-label = Cyfrwng
+perftools-presets-media-description2 = Y rhagosodiad ar gyfer ymchwilio i wallau sain a fideo yn { -brand-shorter-name }.
+
+perftools-presets-networking-label = Rhwydweithio
+perftools-presets-networking-description = Y rhagosodiad ar gyfer ymchwilio i wallau graffeg yn { -brand-shorter-name }
+
+# "Power" is used in the sense of energy (electricity used by the computer).
+perftools-presets-power-label = Pŵer
+perftools-presets-power-description = Y rhagosodiad ar gyfer ymchwilio i wallau defnydd pŵer yn { -brand-shorter-name }, gyda gorbenion isel.
+
+perftools-presets-custom-label = Cyfaddas
+
+##
+
diff --git a/thunderbird-l10n/cy/localization/cy/devtools/client/storage.ftl b/thunderbird-l10n/cy/localization/cy/devtools/client/storage.ftl
new file mode 100644
index 0000000000..7d866e8fa9
--- /dev/null
+++ b/thunderbird-l10n/cy/localization/cy/devtools/client/storage.ftl
@@ -0,0 +1,132 @@
+# This Source Code Form is subject to the terms of the Mozilla Public
+# License, v. 2.0. If a copy of the MPL was not distributed with this
+# file, You can obtain one at http://mozilla.org/MPL/2.0/.
+
+
+### These strings are used inside the Storage Inspector.
+
+# Key shortcut used to focus the filter box on top of the data view
+storage-filter-key = CmdOrCtrl+F
+
+# Hint shown when the selected storage host does not contain any data
+storage-table-empty-text = Dim data'n bresennol ar gyfer y gwesteiwr hwn
+
+# Hint shown when the cookies storage type is selected. Clicking the link will open
+# https://developer.mozilla.org/docs/Tools/Storage_Inspector/Cookies
+storage-table-type-cookies-hint = Gweld a golygu cwcis trwy ddewis gwesteiwr. <a data-l10n-name="learn-more-link">Dysgu mwy</a>
+
+# Hint shown when the local storage type is selected. Clicking the link will open
+# https://developer.mozilla.org/docs/Tools/Storage_Inspector/Local_Storage_Session_Storage
+storage-table-type-localstorage-hint = Gweld a golygu'r storio lleol trwy ddewis gwesteiwr. <a data-l10n-name="learn-more-link">Dysgu mwy</a>
+
+# Hint shown when the session storage type is selected. Clicking the link will open
+# https://developer.mozilla.org/docs/Tools/Storage_Inspector/Local_Storage_Session_Storage
+storage-table-type-sessionstorage-hint = Gweld a golygu storio'r sesiwn trwy ddewis gwesteiwr. <a data-l10n-name="learn-more-link">Dysgu mwy</a>
+
+# Hint shown when the IndexedDB storage type is selected. Clicking the link will open
+# https://developer.mozilla.org/docs/Tools/Storage_Inspector/IndexedDB
+storage-table-type-indexeddb-hint = Gweld a dileu cofnodion IndexedDB trwy ddewis cronfa ddata. <a data-l10n-name="learn-more-link">Dysgu mwy</a>
+
+# Hint shown when the cache storage type is selected. Clicking the link will open
+# https://developer.mozilla.org/docs/Tools/Storage_Inspector/Cache_Storage
+storage-table-type-cache-hint = Gweld a dileu'r cofnodion storio storfa trwy ddewis storfa. <a data-l10n-name="learn-more-link">Dysgu mwy</a>
+
+# Hint shown when the extension storage type is selected. Clicking the link will open
+# https://developer.mozilla.org/docs/Tools/Storage_Inspector/Extension_Storage
+storage-table-type-extensionstorage-hint = Gweld a golygu storfa'r estyniad trwy ddewis gwesteiwr. <a data-l10n-name="learn-more-link">Dysgu mwy</a>
+
+# Placeholder for the searchbox that allows you to filter the table items
+storage-search-box =
+    .placeholder = Hidlo eitemau
+
+# Placeholder text in the sidebar search box
+storage-variable-view-search-box =
+    .placeholder = Gwerthoedd hidl
+
+# Add Item button title
+storage-add-button =
+    .title = Ychwanegu Eitem
+
+# Refresh button title
+storage-refresh-button =
+    .title = Adnewyddu eitemau
+
+# Context menu action to delete all storage items
+storage-context-menu-delete-all =
+    .label = Dileu'r Cyfan
+
+# Context menu action to delete all session cookies
+storage-context-menu-delete-all-session-cookies =
+    .label = Dileu Pob Cwci Sesiwn
+
+# Context menu action to copy a storage item
+storage-context-menu-copy =
+    .label = Copïo
+
+# Context menu action to delete storage item
+# Variables:
+#   $itemName (String) - Name of the storage item that will be deleted
+storage-context-menu-delete =
+    .label = Dileu “{ $itemName }”
+
+# Context menu action to add an item
+storage-context-menu-add-item =
+    .label = Ychwanegu Eitem
+
+# Context menu action to delete all storage items from a given host
+# Variables:
+#   $host (String) - Host for which we want to delete the items
+storage-context-menu-delete-all-from =
+    .label = Dileu Popeth o “{ $host }”
+
+## Header names of the columns in the Storage Table for each type of storage available
+## through the Storage Tree to the side.
+
+storage-table-headers-cookies-name = Enw
+storage-table-headers-cookies-value = Gwerth
+storage-table-headers-cookies-expires = Daw i ben / Oed-Uchaf
+storage-table-headers-cookies-size = Maint
+storage-table-headers-cookies-last-accessed = Mynediad Diwethaf
+storage-table-headers-cookies-creation-time = Crëwyd
+storage-table-headers-cache-status = Statws
+storage-table-headers-extension-storage-area = Ardal Storio
+
+## Labels for Storage type groups present in the Storage Tree, like cookies, local storage etc.
+
+storage-tree-labels-cookies = Cwcis
+storage-tree-labels-local-storage = Storfa Leol
+storage-tree-labels-session-storage = Storfa Sesiwn
+storage-tree-labels-indexed-db = Cronfa Ddata wedi ei Fynegeio
+storage-tree-labels-cache = Storfa'r Storio Dros Dro
+storage-tree-labels-extension-storage = Storio Estyniad
+
+##
+
+# Tooltip for the button that collapses the right panel in the
+# storage UI when the panel is closed.
+storage-expand-pane =
+    .title = Ehangu Paen
+
+# Tooltip for the button that collapses the right panel in the
+# storage UI when the panel is open.
+storage-collapse-pane =
+    .title = Cau Paen
+
+# String displayed in the expires column when the cookie is a Session Cookie
+storage-expires-session = Sesiwn
+
+# Heading displayed over the item value in the sidebar
+storage-data = Data
+
+# Heading displayed over the item parsed value in the sidebar
+storage-parsed-value = Gwerth Didoli
+
+# Warning notification when IndexedDB database could not be deleted immediately.
+# Variables:
+#   $dbName (String) - Name of the database
+storage-idb-delete-blocked = Bydd y gronfa ddata “{ $dbName }” yn cael ei ddileu ar ôl cau pob cysylltiadau.
+
+# Error notification when IndexedDB database could not be deleted.
+# Variables:
+#   $dbName (String) - Name of the database
+storage-idb-delete-error = Nid oedd modd dileu cronfa ddata “{ $dbName }”.
diff --git a/thunderbird-l10n/cy/localization/cy/devtools/client/styleeditor.ftl b/thunderbird-l10n/cy/localization/cy/devtools/client/styleeditor.ftl
new file mode 100644
index 0000000000..a0e2774e0c
--- /dev/null
+++ b/thunderbird-l10n/cy/localization/cy/devtools/client/styleeditor.ftl
@@ -0,0 +1,60 @@
+# This Source Code Form is subject to the terms of the Mozilla Public
+# License, v. 2.0. If a copy of the MPL was not distributed with this
+# file, You can obtain one at http://mozilla.org/MPL/2.0/.
+
+styleeditor-new-button =
+    .tooltiptext = Creu ac atodi dalen arddull newydd i'r ddogfen
+    .accesskey = N
+styleeditor-import-button =
+    .tooltiptext = Mewnforio ac atodi dalen arddull cyfredol i'r ddogfen
+    .accesskey = M
+styleeditor-filter-input =
+    .placeholder = Hidlo dalennau arddull
+styleeditor-visibility-toggle =
+    .tooltiptext = Toglo gwelwdedd tudalen arddull
+    .accesskey = C
+styleeditor-visibility-toggle-system =
+    .tooltiptext = Nid oes modd analluogi dalennau arddull system
+styleeditor-save-button = Cadw
+    .tooltiptext = Cadw'r ddalen arddull i ffeil
+    .accesskey = C
+styleeditor-options-button =
+    .tooltiptext = Dewisiadau'r Golygydd Arddull
+styleeditor-at-rules = At-reolau
+styleeditor-editor-textbox =
+    .data-placeholder = Teipio'r CSS yma.
+styleeditor-no-stylesheet = Nid oes gan y dudalen ddalen arddull.
+styleeditor-no-stylesheet-tip = Efallai'r hoffech chi <a data-l10n-name="append-new-stylesheet">atodi dalen arddull newydd</a>?
+styleeditor-open-link-new-tab =
+    .label = Agor Dolen mewn Tab Newydd
+styleeditor-copy-url =
+    .label = Copïo URL
+styleeditor-find =
+    .label = Canfod
+    .accesskey = f
+styleeditor-find-again =
+    .label = Canfod Eto
+    .accesskey = a
+styleeditor-go-to-line =
+    .label = Neidio i linell…
+    .accesskey = N
+# Label displayed when searching a term that is not found in any stylesheet path
+styleeditor-stylesheet-all-filtered = Dim dalennau arddull cyfatebol.
+# This string is shown in the style sheets list
+# Variables:
+#   $ruleCount (Integer) - The number of rules in the stylesheet.
+styleeditor-stylesheet-rule-count =
+    { $ruleCount ->
+        [zero] Dim rheolau.
+        [one] { $ruleCount } rheol.
+        [two] { $ruleCount } reol.
+        [few] { $ruleCount } rheol.
+        [many] { $ruleCount } rheol.
+       *[other] { $ruleCount } rheol.
+    }
+# Title for the pretty print button in the editor footer.
+styleeditor-pretty-print-button =
+    .title = Dalen arddull pretty print
+# Title for the pretty print button in the editor footer, when it's disabled
+styleeditor-pretty-print-button-disabled =
+    .title = Dim ond yn gallu argraffu pretty print ffeiliau CSS
diff --git a/thunderbird-l10n/cy/localization/cy/devtools/client/toolbox-options.ftl b/thunderbird-l10n/cy/localization/cy/devtools/client/toolbox-options.ftl
new file mode 100644
index 0000000000..4aa16408ce
--- /dev/null
+++ b/thunderbird-l10n/cy/localization/cy/devtools/client/toolbox-options.ftl
@@ -0,0 +1,154 @@
+# This Source Code Form is subject to the terms of the Mozilla Public
+# License, v. 2.0. If a copy of the MPL was not distributed with this
+# file, You can obtain one at http://mozilla.org/MPL/2.0/.
+
+
+### Localization for Developer Tools options
+
+
+## Default Developer Tools section
+
+# The heading
+options-select-default-tools-label = Offer Datblygu Firefox Rhagosodedig
+
+# The label for the explanation of the * marker on a tool which is currently not supported
+# for the target of the toolbox.
+options-tool-not-supported-label = * Dim cefnogaeth ar gyfer targed y blwch offer cyfredol
+
+# The label for the heading of group of checkboxes corresponding to the developer tools
+# added by add-ons. This heading is hidden when there is no developer tool installed by add-ons.
+options-select-additional-tools-label = Offer Datblygu wedi eu gosod gan ychwanegion
+
+# The label for the heading of group of checkboxes corresponding to the default developer
+# tool buttons.
+options-select-enabled-toolbox-buttons-label = Botymau Blwch Offer sydd ar Gael
+
+# The label for the heading of the radiobox corresponding to the theme
+options-select-dev-tools-theme-label = Themâu
+
+## Inspector section
+
+# The heading
+options-context-inspector = Archwiliwr
+
+# The label for the checkbox option to show user agent styles
+options-show-user-agent-styles-label = Dangos Arddulliau Porwr
+options-show-user-agent-styles-tooltip =
+    .title = Bydd cychwyn hwn yn dangos yr arddulliau rhagosodedig sy'n cael eu llwytho gan y porwr.
+
+# The label for the checkbox option to enable collapse attributes
+options-collapse-attrs-label = Tocio priodoleddau DOM
+options-collapse-attrs-tooltip =
+    .title = Tocio'r priodoleddau hir yn yr arolygydd
+
+# The label for the checkbox option to enable the "drag to update" feature
+options-inspector-draggable-properties-label = Cliciwch a llusgwch i olygu gwerthoedd maint
+options-inspector-draggable-properties-tooltip =
+    .title = Cliciwch a llusgwch i olygu gwerthoedd maint yng ngolwg rheolau'r arolygydd.
+
+# The label for the checkbox option to enable simplified highlighting on page elements
+# within the inspector for users who enabled prefers-reduced-motion = reduce
+options-inspector-simplified-highlighters-label = Defnyddiwch amlygwyr symlach gyda prefers-reduced-motion
+options-inspector-simplified-highlighters-tooltip =
+    .title = Yn galluogi amlygwyr symlach pan fydd prefers-reduced-motion wedi'i alluogi. Bydd yn tynnu llinellau yn lle petryalau wedi'u llenwi o amgylch elfennau wedi'u hamlygu er mwyn osgoi effeithiau fflachio.
+
+## "Default Color Unit" options for the Inspector
+
+options-default-color-unit-label = Uned lliw rhagnodedig
+options-default-color-unit-authored = Fel ei Awduro
+options-default-color-unit-hex = Hecs
+options-default-color-unit-hsl = HSL(A)
+options-default-color-unit-rgb = RGB(A)
+options-default-color-unit-hwb = HWB
+options-default-color-unit-name = Enw Lliwiau
+
+## Style Editor section
+
+# The heading
+options-styleeditor-label = Golygydd Arddull
+
+# The label for the checkbox that toggles autocompletion of css in the Style Editor
+options-stylesheet-autocompletion-label = Awtogwblhau CSS
+options-stylesheet-autocompletion-tooltip =
+    .title = Awtogwblhau priodweddau CSS, gwerthoedd a dewiswyr yn y Golygydd Steil wrth i chi deipio
+
+## Screenshot section
+
+# The heading
+options-screenshot-label = Ymddygiad Llun Sgrin
+
+# Label for the checkbox that toggles screenshot to clipboard feature
+options-screenshot-clipboard-only-label = Llun sgrin i'r clipfwrdd yn unig
+options-screenshot-clipboard-tooltip2 =
+    .title = Yn cadw i'r llun sgrin yn uniongyrchol i'r clipfwrdd
+
+# Label for the checkbox that toggles the camera shutter audio for screenshot tool
+options-screenshot-audio-label = Chwarae sain caead camera
+options-screenshot-audio-tooltip =
+    .title = Galluogi sain camera wrth gymryd llun sgrin
+
+## Editor section
+
+# The heading
+options-sourceeditor-label = Dewisiadau Golygu
+
+options-sourceeditor-detectindentation-tooltip =
+    .title = Dyfalu mewnoliad ar sail cynnwys y ffynhonnell
+options-sourceeditor-detectindentation-label = Canfod mewnoliad
+options-sourceeditor-autoclosebrackets-tooltip =
+    .title = Gosod bracedi cau yn awtomatig
+options-sourceeditor-autoclosebrackets-label = Cau bracedi'n awtomatig
+options-sourceeditor-expandtab-tooltip =
+    .title = Defnyddio bylchau yn lle nod tab
+options-sourceeditor-expandtab-label = Mewnoli gan ddefnyddio bylchau
+options-sourceeditor-tabsize-label = Maint tab
+options-sourceeditor-keybinding-label = Rhwymwyr allwedd
+options-sourceeditor-keybinding-default-label = Rhagosodiad
+
+## Advanced section
+
+# The heading (this item is also used in perftools.ftl)
+options-context-advanced-settings = Gosodiadau uwch
+
+# The label for the checkbox that toggles the HTTP cache on or off
+options-disable-http-cache-label = Analluogi Storfa Dros Dro HTTP (pan mae'r blwch offer ar agor)
+options-disable-http-cache-tooltip =
+    .title = Bydd cychwyn y dewis hwn yn analluogi storfa dros dro'r HTTP ar gyfer pob tab sydd a' r blwch offer ar agor. Nid yw Service Workers yn cael eu heffeithio gan y dewis hwn.
+
+# The label for checkbox that toggles JavaScript on or off
+options-disable-javascript-label = Analluogi JavaScript *
+options-disable-javascript-tooltip =
+    .title = Bydd cychwyn y nodwedd hon yn analluogi JavaScript yn y tab cyfredol. Os fydd y tab neu’r blwch offer yn cael eu cau yna bydd y gosodiad hwn yn cael ei anghofio.
+
+# The label for checkbox that toggles chrome debugging, i.e. the devtools.chrome.enabled preference
+options-enable-chrome-label = Galluogi chrome y porwr ac ychwanegion blychau offer dadfygio
+options-enable-chrome-tooltip =
+    .title = Bydd cychwyn y dewis hwn yn caniatáu i chi ddefnyddio offer datblygwyr amrywiol o fewn cyd-destun porwr (drwy Offer > Datblygwr Gwe > Blwch Offer y Porwr) a dadfygio ychwanegion o'r Rheolwr Ychwanegion
+
+# The label for checkbox that toggles remote debugging, i.e. the devtools.debugger.remote-enabled preference
+options-enable-remote-label = Galluogi dadfygio pell
+options-enable-remote-tooltip2 =
+    .title = Bydd troi'r dewis hwn ymlaen yn caniatáu dadfygio enghraifft y porwr hwn o bell
+
+# The label for checkbox that enables F12 as a shortcut to open DevTools
+options-enable-f12-label = Defnyddiwch y fysell F12 i agor neu gau DevTools
+options-enable-f12-tooltip =
+    .title = Bydd troi'r dewis hwn ymlaen yn rhwymo'r fysell F12 i agor neu gau blwch offer DevTools
+
+# The label for checkbox that toggles custom formatters for objects
+options-enable-custom-formatters-label = Galluogi fformatwyr cyfaddas
+options-enable-custom-formatters-tooltip =
+    .title = Bydd troi'r dewis hwn ymlaen yn caniatáu i wefannau ddiffinio fformatwyr personol ar gyfer gwrthrychau DOM
+
+# The label for checkbox that toggles the service workers testing over HTTP on or off.
+options-enable-service-workers-http-label = Galluogi Service Workers dros HTTP (pan fydd y blwch offer ar agor)
+options-enable-service-workers-http-tooltip =
+    .title = Bydd cychwyn y dewis wn yn caniatáu i nodwedd service workers dros HTTP ar gyfer pob tab sydd â blwch offer ar agor.
+
+# The label for the checkbox that toggles source maps in all tools.
+options-source-maps-label = Galluogi Mapiau Ffynhonnell
+options-source-maps-tooltip =
+    .title = Os ydych yn galluogi'r dewis hwn bydd ffenylalanin cael eu mapio yn yr offer.
+
+# The message shown for settings that trigger page reload
+options-context-triggers-page-refresh = * Sesiwn gyfredol yn unig, ail-lwytho'r dudalen
diff --git a/thunderbird-l10n/cy/localization/cy/devtools/client/toolbox.ftl b/thunderbird-l10n/cy/localization/cy/devtools/client/toolbox.ftl
new file mode 100644
index 0000000000..b607d9a2d7
--- /dev/null
+++ b/thunderbird-l10n/cy/localization/cy/devtools/client/toolbox.ftl
@@ -0,0 +1,55 @@
+# This Source Code Form is subject to the terms of the Mozilla Public
+# License, v. 2.0. If a copy of the MPL was not distributed with this
+# file, You can obtain one at http://mozilla.org/MPL/2.0/.
+
+
+### These messages are used in the DevTools toolbox.
+
+
+## These labels are shown in the "..." menu in the toolbox, and represent different
+## commands such as the docking of DevTools, toggling features, and viewing some
+## external links. Some of the commands have the keyboard shortcut shown next to
+## the label.
+
+toolbox-meatball-menu-dock-bottom-label = Docio i'r gwaelod
+toolbox-meatball-menu-dock-left-label = Docio i'r chwith
+toolbox-meatball-menu-dock-right-label = Docio i'r dde
+toolbox-meatball-menu-dock-separate-window-label = Ffenestr ar wahân
+
+toolbox-meatball-menu-splitconsole-label = Dangos Consol Hollt
+toolbox-meatball-menu-hideconsole-label = Cuddio'r consol hollt
+
+toolbox-meatball-menu-settings-label = Gosodiadau
+toolbox-meatball-menu-documentation-label = Dogfennaeth…
+toolbox-meatball-menu-community-label = Cymuned…
+
+# This menu item is only available in the browser toolbox. It forces the popups/panels
+# to stay visible on blur, which is primarily useful for addon developers and Firefox
+# contributors.
+toolbox-meatball-menu-noautohide-label = Analluogi awtoguddio llamlenni
+
+toolbox-meatball-menu-pseudo-locale-accented = Galluogi locale “acennog”.
+toolbox-meatball-menu-pseudo-locale-bidi = Galluogi locale “bidi”.
+
+##
+
+
+## These labels are shown in the top-toolbar in the Browser Toolbox and Browser Console
+
+toolbox-mode-browser-toolbox-label = Modd Blwch Offer Porwr
+toolbox-mode-browser-console-label = Modd Consol Porwr
+
+toolbox-mode-everything-label = Amlbroses
+toolbox-mode-everything-sub-label = (Arafach)
+toolbox-mode-everything-container =
+    .title = Dadfygio popeth ym mhob proses
+
+toolbox-mode-parent-process-label = Proses rhiant yn unig
+toolbox-mode-parent-process-sub-label = (Cyflym)
+toolbox-mode-parent-process-container =
+    .title = Canolbwyntio ar adnoddau o'r broses rhiant yn unig.
+
+toolbox-always-on-top-enabled2 = Analluogau bob tro ar y brig
+    .title = Bydd hyn yn ail-gychwyn yr Offer Datblygwyr
+toolbox-always-on-top-disabled2 = Galluogi bob tro ar y brig
+    .title = Bydd hyn yn ail-gychwyn yr Offer Datblygwyr
diff --git a/thunderbird-l10n/cy/localization/cy/devtools/client/tooltips.ftl b/thunderbird-l10n/cy/localization/cy/devtools/client/tooltips.ftl
new file mode 100644
index 0000000000..cccaa5ae02
--- /dev/null
+++ b/thunderbird-l10n/cy/localization/cy/devtools/client/tooltips.ftl
@@ -0,0 +1,105 @@
+# This Source Code Form is subject to the terms of the Mozilla Public
+# License, v. 2.0. If a copy of the MPL was not distributed with this
+# file, You can obtain one at http://mozilla.org/MPL/2.0/.
+
+
+### Localization for Developer Tools tooltips.
+
+learn-more = <span data-l10n-name ="link">Darllen rhagor</span>
+
+## In the Rule View when a CSS property cannot be successfully applied we display
+## an icon. When this icon is hovered this message is displayed to explain why
+## the property is not applied.
+## Variables:
+##   $property (string) - A CSS property name e.g. "color".
+##   $display (string) - A CSS display value e.g. "inline-block".
+
+inactive-css-not-grid-or-flex-container = Nid yw <strong>{ $property }</strong> yn effeithio ar yr elfen hon gan nad yw'n gynhwysydd flex nac yn gynhwysydd grid.
+inactive-css-not-grid-or-flex-container-or-multicol-container = Nid yw <strong>{ $property }</strong> yn effeithio ar yr elfen hon gan nad yw'n gynhwysydd fflecs, yn gynhwysydd grid, neu'n gynhwysydd aml-golofn.
+inactive-css-not-multicol-container = Nid yw <strong>{ $property }</strong> yn cael unrhyw effaith ar yr elfen hon gan nad yw'n gynhwysydd aml-golofn.
+inactive-css-not-grid-or-flex-item = Nid yw <strong>{ $property }</strong> yn effeithio ar yr elfen hon gan nad yw'n grid nac yn eitem flex.
+inactive-css-not-grid-item = Nid yw <strong>{ $property }</strong> yn effeithio ar yr elfen hon gan nad yw'n eitem grid.
+inactive-css-not-grid-container = Nid yw <strong>{ $property }</strong> yn effeithio ar yr elfen hon gan nad yw'n gynhwysydd grid.
+inactive-css-not-flex-item = Nid yw <strong>{ $property }</strong> yn cael unrhyw effaith ar yr elfen hon gan nad yw'n eitem hyblyg.
+inactive-css-not-flex-container = Nid yw <strong>{ $property }</strong> yn effeithio ar yr elfen hon gan nad yw'n gynhwysydd flex.
+inactive-css-not-inline-or-tablecell = Nid yw <strong> { $property } </strong> yn cael unrhyw effaith ar yr elfen hon gan nad yw'n elfen mewnlin neu gell tabl.
+inactive-css-first-line-pseudo-element-not-supported = Nid yw <strong>{ $property }</strong> yn cael ei gefnogi ar ::first-line pseudo-elements.
+inactive-css-first-letter-pseudo-element-not-supported = Nid yw <strong>{ $property }</strong> yn cael ei gefnogi ar ::first-line pseudo-elements.
+inactive-css-placeholder-pseudo-element-not-supported = Nid yw <strong>{ $property }</strong> yn cael ei gefnogi ar ::placeholder pseudo-elements.
+inactive-css-property-because-of-display = Nid oes gan <strong>{ $property }</strong> unrhyw effaith ar yr elfen hon gan ei bod yn dangos  <strong>{ $display }</strong>.
+inactive-css-not-display-block-on-floated = Mae'r peiriant wedi newid y gwerth <strong>display</strong> i <strong>block</strong> oherwydd bod yr elfen yn <strong>arnofio</strong>.
+inactive-css-property-is-impossible-to-override-in-visited = Mae'n amhosib diystyru <strong>{ $property }</strong> oherwydd cyfyngiadau <strong>:visited</strong>.
+inactive-css-position-property-on-unpositioned-box = Nid yw <strong>{ $property }</strong> yn effeithio ar yr elfen hon gan nad yw'n eitem wedi'i lleoli.
+inactive-text-overflow-when-no-overflow = Nid yw <strong>{ $property }</strong> yn cael unrhyw effaith ar yr elfen hon gan nad yw <strong>overflow:hidden</strong> wedi'i osod.
+inactive-css-not-for-internal-table-elements = Nid yw <strong>{ $property }</strong> yn cael unrhyw effaith ar elfennau tablau mewnol.
+inactive-css-not-for-internal-table-elements-except-table-cells = Nid yw <strong>{ $property }</strong> yn cael unrhyw effaith ar elfennau bwrdd mewnol ac eithrio celloedd bwrdd.
+inactive-css-not-table = Nid yw <strong>{ $property }</strong> yn effeithio ar yr elfen hon gan nad yw'n dabl.
+inactive-css-not-table-cell = Nid yw <strong>{ $property }</strong> yn cael unrhyw effaith ar yr elfen hon gan nad yw'n gell tabl.
+inactive-scroll-padding-when-not-scroll-container = Nid yw <strong>{ $property }</strong> yn cael unrhyw effaith ar yr elfen hon gan nad yw'n sgrolio.
+inactive-css-border-image = Nid yw <strong>{ $property }</strong> yn cael unrhyw effaith ar yr elfen hon gan nad oes modd ei gymhwyso i elfennau tabl mewnol lle mae <strong>cwymp-ffiniol</strong> wedi'i osod i <strong>gwympo</strong> ar y elfen tabl rhiant.
+inactive-css-ruby-element = Nid yw <strong>{ $property }</strong> yn effeithio ar yr elfen hon gan ei bod yn elfen ruby. Mae ei faint yn cael ei bennu gan faint ffont y testun ruby.
+inactive-css-highlight-pseudo-elements-not-supported = Nid yw <strong>{ $property }</strong> yn cael ei gefnogi ar amlygu ffug-elfennau.
+inactive-css-cue-pseudo-element-not-supported = Nid yw <strong>{ $property }</strong> yn cael ei gefnogi ar  ::cue pseudo-elements.
+# Variables:
+#   $lineCount (integer) - The number of lines the element has.
+inactive-css-text-wrap-balance-lines-exceeded =
+    { $lineCount ->
+        [zero] Nid yw <strong>{ $property }</strong> yn effeithio ar yr elfen hon oherwydd mae ganddi fwy na { $lineCount } llinell.
+        [one] Nid yw <strong>{ $property }</strong> yn effeithio ar yr elfen hon oherwydd mae ganddi fwy na { $lineCount } llinell.
+        [two] Nid yw <strong>{ $property }</strong> yn effeithio ar yr elfen hon oherwydd mae ganddi fwy na { $lineCount } llinell.
+        [few] Nid yw <strong>{ $property }</strong> yn effeithio ar yr elfen hon oherwydd mae ganddi fwy na { $lineCount } llinell.
+        [many] Nid yw <strong>{ $property }</strong> yn effeithio ar yr elfen hon oherwydd mae ganddi fwy na { $lineCount } llinell.
+       *[other] Nid yw <strong>{ $property }</strong> yn effeithio ar yr elfen hon oherwydd mae ganddi fwy na { $lineCount } llinell.
+    }
+inactive-css-text-wrap-balance-fragmented = Nid yw <strong>{ $property }</strong> yn effeithio ar yr elfen hon oherwydd ei bod yn dameidiog, h.y. mae ei chynnwys wedi'i rhannu ar draws colofnau neu dudalennau lluosog.
+
+## In the Rule View when a CSS property cannot be successfully applied we display
+## an icon. When this icon is hovered this message is displayed to explain how
+## the problem can be solved.
+
+inactive-css-not-grid-or-flex-container-fix = Ceisiwch ychwanegu <strong>display:grid</strong> neu <strong>display:flex</strong>. { learn-more }
+inactive-css-not-grid-or-flex-container-or-multicol-container-fix = Ceisiwch ychwanegu naill ai <strong>display:grid</strong>, <strong>display:flex</strong>, neu <strong>columns:2</strong>. { learn-more }
+inactive-css-not-multicol-container-fix = Ceisiwch ychwanegu <strong>column-count</strong> neu <strong>column-width</strong>. { learn-more }
+inactive-css-not-grid-or-flex-item-fix-3 = Ceisiwch ychwanegu <strong>display:grid</strong>, <strong>display:flex</strong>, <strong>display:inline-grid</strong> neu <strong>display:inline-flex</strong> i riant yr elfen. { learn-more }
+inactive-css-not-grid-item-fix-2 = Ceisiwch ychwanegu <strong>display:grid</strong> neu <strong>display:inline-grid</strong> at riant yr elfen. { learn-more }
+inactive-css-not-grid-container-fix = Ceisiwch ychwanegu <strong>display:grid</strong> neu <strong>display:inline-grid</strong>. { learn-more }
+inactive-css-not-flex-item-fix-2 = Ceisiwch ychwanegu <strong>display:flex</strong> neu <strong>display:inline-flex</strong> i riant yr elfen. { learn-more }
+inactive-css-not-flex-container-fix = Ceisiwch ychwanegu <strong>display:flex</strong> neu <strong>display:inline-flex</strong>. { learn-more }
+inactive-css-not-inline-or-tablecell-fix = Ceisiwch ychwanegu <strong>display:inline</strong> neu <strong>display:table-cell</strong>. { learn-more }
+inactive-css-non-replaced-inline-or-table-row-or-row-group-fix = Ceisiwch ychwanegu <strong>display:inline-block</strong> neu <strong>display:block</strong>. { learn-more }
+inactive-css-non-replaced-inline-or-table-column-or-column-group-fix = Ceisiwch ychwanegu <strong>display:inline-block</strong>. { learn-more }
+inactive-css-not-display-block-on-floated-fix = Ceisiwch dynnu <strong>float</strong> neu <strong>display:block</strong>. { learn-more }
+inactive-css-position-property-on-unpositioned-box-fix = Ceisiwch osod priodwedd ei <strong>leoliad</strong> i rywbeth arall heblaw <strong>statig</strong>. { learn-more }
+inactive-text-overflow-when-no-overflow-fix = Ceisiwch ychwanegu <strong>overflow:hidden</strong>. { learn-more }
+inactive-css-not-for-internal-table-elements-fix = Ceisiwch osod ei briodwedd <strong>arddangos</strong> i rywbeth arall heblaw <strong>cell-tabl</strong>, <strong>colofn-tabl</strong>, <strong>rhes-tabl</strong>, <strong>tabl-colofn-grŵp</strong>, <strong>tabl-rhes-grŵp</strong>, neu <strong>tabl-troedyn-grŵp</strong>. { learn-more }
+inactive-css-not-for-internal-table-elements-except-table-cells-fix = Ceisiwch osod ei briodwedd <strong>arddangos</strong> i rywbeth arall heblaw <strong>colofn-tabl</strong>, <strong>rhes-tabl</strong>, <strong>tabl-colofn-grŵp</strong>, <strong>tabl-rhes-grŵp</strong>, neu <strong>tabl-troedyn-grŵp</strong>. { learn-more }
+inactive-css-not-table-fix = Ceisiwch ychwanegu <strong>display:table</strong> neu <strong>display:inline-table</strong>. { learn-more }
+inactive-css-not-table-cell-fix = Ceisiwch ychwanegu <strong>display:table-cell</strong>. { learn-more }
+inactive-scroll-padding-when-not-scroll-container-fix = Ceisiwch ychwanegu <strong>overflow:auto</strong>, <strong>overflow:scroll</strong> neu <strong>overflow:hidden</strong>. { learn-more }
+inactive-css-border-image-fix = Ar yr elfen tabl rhiant, tynnwch y briodwedd neu newidiwch werth <strong>cwymp-ffiniol</strong> i werth heblaw <strong>cwymp</strong>. { learn-more }
+inactive-css-ruby-element-fix = Ceisio newid <strong>maint ffont</strong> y testun ruby. { learn-more }
+inactive-css-text-wrap-balance-lines-exceeded-fix = Ceisiwch leihau nifer y llinellau.{ learn-more }
+inactive-css-text-wrap-balance-fragmented-fix = Osgowch hollti cynnwys yr elfen e.e. drwy dynnu'r colofnau neu drwy ddefnyddio <strong>page-break-inside:avoid</strong>.{ learn-more }
+
+## In the Rule View when a CSS property may have compatibility issues with other browsers
+## we display an icon. When this icon is hovered this message is displayed to explain why
+## the property is incompatible and the platforms it is incompatible on.
+## Variables:
+##   $property (string) - A CSS declaration name e.g. "-moz-user-select" that can be a platform specific alias.
+##   $rootProperty (string) - A raw CSS property name e.g. "user-select" that is not a platform specific alias.
+
+css-compatibility-default-message = Nid yw <strong>{ $property }</strong> yn cael ei gefnogi gan y porwyr canlynol:
+css-compatibility-deprecated-experimental-message = Roedd <strong>{ $property }</strong> yn briodoledd arbrofol sydd bellach yn cael ei anghymeradwyo gan safonau'r W3C. Nid yw'n cael ei gefnogi gan y porwyr canlynol:
+css-compatibility-deprecated-experimental-supported-message = Roedd <strong>{ $property }</strong> yn briodwedd arbrofol sydd bellach yn cael ei anghymeradwyo gan safonau'r W3C.
+css-compatibility-deprecated-message = Mae <strong>{ $property }</strong> yn cael ei anghymeradwyo gan safonau'r W3C. Nid yw'n cael ei gefnogi gan y porwyr canlynol:
+css-compatibility-deprecated-supported-message = Mae <strong>{ $property }</strong> yn cael ei anghymeradwyo gan safonau'r W3C.
+css-compatibility-experimental-message = Mae <strong>{ $property }</strong> yn briodwedd arbrofol. Nid yw'n cael ei gefnogi gan y porwyr canlynol:
+css-compatibility-experimental-supported-message = Mae <strong>{ $property }</strong> yn briodwedd arbrofol.
+css-compatibility-learn-more-message = <span data-l10n-name="link">Darllen rhagor</span> am <strong>{ $rootProperty }</strong>
+
+## In the Rule View when a rule selector can causes issues, we display an icon.
+## When this icon is hovered one or more of those messages are displayed to explain what
+## the issue are.
+
+# :has() should not be translated
+css-selector-warning-unconstrained-has = Mae'r dewisydd hwn yn defnyddio <strong>:has()</strong> heb ei gyfyngu, a all fod yn araf
diff --git a/thunderbird-l10n/cy/localization/cy/devtools/shared/debugger-paused-reasons.ftl b/thunderbird-l10n/cy/localization/cy/devtools/shared/debugger-paused-reasons.ftl
new file mode 100644
index 0000000000..a48c229fb0
--- /dev/null
+++ b/thunderbird-l10n/cy/localization/cy/devtools/shared/debugger-paused-reasons.ftl
@@ -0,0 +1,87 @@
+# This Source Code Form is subject to the terms of the Mozilla Public
+# License, v. 2.0. If a copy of the MPL was not distributed with this
+# file, You can obtain one at http://mozilla.org/MPL/2.0/.
+
+
+### These strings are used inside the Debugger which is available from the Web
+### Developer sub-menu -> 'Debugger', as well as in the "Paused Debugger
+### Overlay" that is displayed in the content page when it pauses.
+
+
+### The correct localization of this file might be to keep it in
+### English, or another language commonly spoken among web developers.
+### You want to make that choice consistent across the developer tools.
+### A good criteria is the language in which you'd find the best
+### documentation on web development on the web.
+
+# The text that is displayed in a info block explaining how the debugger is
+# currently paused due to a `debugger` statement in the code
+whypaused-debugger-statement = Oedwyd ar ddatganiad dadfygiwr
+
+# The text that is displayed in a info block explaining how the debugger is
+# currently paused on a breakpoint
+whypaused-breakpoint = Oedwyd ar dorbwynt
+
+# The text that is displayed in a info block explaining how the debugger is
+# currently paused on an event breakpoint.
+whypaused-event-breakpoint = Oedwyd ar dorbwynt digwyddiad
+
+# The text that is displayed in a info block explaining how the debugger is
+# currently paused on an exception
+whypaused-exception = Oedwyd ar eithriad
+
+# The text that is displayed in a info block explaining how the debugger is
+# currently paused on a DOM mutation breakpoint
+whypaused-mutation-breakpoint = Oedwyd ar mudiad DOM
+
+# The text that is displayed to describe an added node which triggers a subtree
+# modification
+whypaused-mutation-breakpoint-added = Ychwanegwyd:
+
+# The text that is displayed to describe a removed node which triggers a subtree
+# modification
+whypaused-mutation-breakpoint-removed = Tynnwyd:
+
+# The text that is displayed in a info block explaining how the debugger is
+# currently paused at a JS execution
+whypaused-interrupted = Oedwyd ar ei Weithredu
+
+# The text that is displayed in a info block explaining how the debugger is
+# currently paused while stepping in or out of the stack
+whypaused-resume-limit = Oedwyd tra'n stepio
+
+# The text that is displayed in a info block explaining how the debugger is
+# currently paused on a dom event
+whypaused-pause-on-dom-events = Oedwyd ar wrandawr digwyddiad
+
+# The text that is displayed in an info block when evaluating a conditional
+# breakpoint throws an error
+whypaused-breakpoint-condition-thrown = Gwall gyda torbwynt amodol
+
+# The text that is displayed in a info block explaining how the debugger is
+# currently paused on an xml http request
+whypaused-xhr = Oedwyd ar XMLHttpRequest
+
+# The text that is displayed in a info block explaining how the debugger is
+# currently paused on a promise rejection
+whypaused-promise-rejection = Oedwyd ar wrthodiad addewid
+
+# The text that is displayed in a info block explaining how the debugger is
+# currently paused at a watchpoint on an object property
+whypaused-get-watchpoint = Wedi'i oedi ar fynediad i briodoledd
+
+# The text that is displayed in an info block explaining how the debugger is
+# currently paused at a watchpoint on an object property
+whypaused-set-watchpoint = Wedi'i oedi ar briodwedd set
+
+# The text that is displayed in a info block explaining how the debugger is
+# currently paused on an assert
+whypaused-assert = Oedwyd ar honiad
+
+# The text that is displayed in a info block explaining how the debugger is
+# currently paused on a debugger statement
+whypaused-debug-command = Oedwyd ar swyddogaeth dadfygio
+
+# The text that is displayed in a info block explaining how the debugger is
+# currently paused on an event listener breakpoint set
+whypaused-other = Oedwyd y dadfygiwr
diff --git a/thunderbird-l10n/cy/localization/cy/devtools/shared/highlighters.ftl b/thunderbird-l10n/cy/localization/cy/devtools/shared/highlighters.ftl
new file mode 100644
index 0000000000..694aa4d8dc
--- /dev/null
+++ b/thunderbird-l10n/cy/localization/cy/devtools/shared/highlighters.ftl
@@ -0,0 +1,67 @@
+# This Source Code Form is subject to the terms of the Mozilla Public
+# License, v. 2.0. If a copy of the MPL was not distributed with this
+# file, You can obtain one at http://mozilla.org/MPL/2.0/.
+
+
+### This file contains strings used in highlighters.
+### Highlighters are visualizations that DevTools draws on top of content to aid
+### in understanding content sizing, etc.
+
+# The row and column position of a grid cell shown in the grid cell infobar when hovering
+# over the CSS grid outline.
+# Variables
+# $row (integer) - The row index
+# $column (integer) - The column index
+grid-row-column-positions = Rhes { $row } / Colofn { $column }
+
+# The layout type of an element shown in the infobar when hovering over a DOM element and
+# it is a grid container.
+gridtype-container = Cynhwysydd Grid
+
+# The layout type of an element shown in the infobar when hovering over a DOM element and
+# it is a grid item.
+gridtype-item = Eitem Grid
+
+# The layout type of an element shown in the infobar when hovering over a DOM element and
+# it is both a grid container and a grid item.
+gridtype-dual = Cynhwysydd Grid/Item
+
+# The layout type of an element shown in the infobar when hovering over a DOM element and
+# it is a flex container.
+flextype-container = Cynhwysydd Flex
+
+# The layout type of an element shown in the infobar when hovering over a DOM element and
+# it is a flex item.
+flextype-item = Eitem Flex
+
+# The layout type of an element shown in the infobar when hovering over a DOM element and
+# it is both a flex container and a flex item.
+flextype-dual = Cynhwysydd Flex/Item
+
+# The message displayed in the content page when the user clicks on the
+# "Pick an element from the page" in about:devtools-toolbox inspector panel, when
+# debugging a remote page.
+# Variables
+# $action (string) - Will either be remote-node-picker-notice-action-desktop or
+#                    remote-node-picker-notice-action-touch
+remote-node-picker-notice = Dewisydd Node DevTools wedi'i alluogi. { $action }
+
+# Text displayed in `remote-node-picker-notice`, when the remote page is on desktop
+remote-node-picker-notice-action-desktop = Cliciwch elfen i'w ddewis yn yr Arolygydd
+
+# Text displayed in `remote-node-picker-notice`, when the remote page is on Android
+remote-node-picker-notice-action-touch = Tapiwch elfen i'w ddewis yn yr Arolygydd
+
+# The text displayed in the button that is in the notice in the content page when the user
+# clicks on the "Pick an element from the page" in about:devtools-toolbox inspector panel,
+# when debugging a remote page.
+remote-node-picker-notice-hide-button = Cuddio
+
+# The text displayed in a toolbox notification message which is only displayed
+# if prefers-reduced-motion is enabled (via OS-level settings or by using the
+# ui.prefersReducedMotion=1 preference).
+simple-highlighters-message = Pan fydd prefers-reduced-motion wedi'i alluogi, mae modd galluogi amlygwyr symlach yn y panel gosodiadau, er mwyn osgoi fflachio lliwiau.
+
+# Text displayed in a button inside the "simple-highlighters-message" toolbox
+# notification. "Settings" here refers to the DevTools settings panel.
+simple-highlighters-settings-button = Agor y Gosodiadau
diff --git a/thunderbird-l10n/cy/localization/cy/devtools/shared/webconsole-commands.ftl b/thunderbird-l10n/cy/localization/cy/devtools/shared/webconsole-commands.ftl
new file mode 100644
index 0000000000..851e6283ae
--- /dev/null
+++ b/thunderbird-l10n/cy/localization/cy/devtools/shared/webconsole-commands.ftl
@@ -0,0 +1,34 @@
+# This Source Code Form is subject to the terms of the Mozilla Public
+# License, v. 2.0. If a copy of the MPL was not distributed with this
+# file, You can obtain one at http://mozilla.org/MPL/2.0/.
+
+
+# These strings are used inside the Web Console commands
+# which can be executed in the Developer Tools, available in the
+# Browser Tools sub-menu -> 'Web Developer Tools'
+
+# Usage string for :block command
+webconsole-commands-usage-block =
+    :block URL_STRING
+    
+    Dechrau rhwystro ceisiadau rhwydwaith
+    
+      Yn derbyn un ymresymiad URLSTRING yn unig, sef llinyn heb ei ddyfynnu a ddefnyddir i rwystro pob cais y mae ei URL yn cynnwys y llinyn hwn.
+      Defnyddiwch :unblock neu far ochr rhwystro cais y Monitor Rhwydwaith i ddadwneud hyn.
+# Usage string for :unblock command
+webconsole-commands-usage-unblock =
+    :unblock URL_STRING
+    
+    Atal rhwystro ceisiadau rhwydwaith
+    
+      Mae'n derbyn un ymresymiad yn unig, yr un llinyn yn union a basiwyd yn flaenorol i :block.
+# Usage string for :trace command
+webconsole-commands-usage-trace =
+    :trace
+    
+    Toglo'r olrhain JavaScript
+    
+      Mae’n cefnogi’r dadleuon canlynol:
+        --logMethod i'w osod i 'console' ar gyfer mewngofnodi i'r consol gwe (y rhagosodiad), neu 'stdout' ar gyfer mewngofnodi i'r allbwn safonol,
+        --prefix Llinyn dewisol a fydd yn cael ei gofnodi o flaen yr holl gofnodion olrhain,
+        --help neu --usage i ddangos y neges hon.
diff --git a/thunderbird-l10n/cy/localization/cy/devtools/startup/key-shortcuts.ftl b/thunderbird-l10n/cy/localization/cy/devtools/startup/key-shortcuts.ftl
new file mode 100644
index 0000000000..bbc2c7ca1e
--- /dev/null
+++ b/thunderbird-l10n/cy/localization/cy/devtools/startup/key-shortcuts.ftl
@@ -0,0 +1,38 @@
+# This Source Code Form is subject to the terms of the Mozilla Public
+# License, v. 2.0. If a copy of the MPL was not distributed with this
+# file, You can obtain one at http://mozilla.org/MPL/2.0/.
+
+# Key pressed to open a toolbox with the default panel selected
+devtools-commandkey-toggle-toolbox = I
+# Alternative key pressed to open a toolbox with the default panel selected
+devtools-commandkey-toggle-toolbox-f12 = VK_F12
+# Key pressed to open the Browser Toolbox, used for debugging Firefox itself
+devtools-commandkey-browser-toolbox = I
+# Key pressed to open the Browser Console, used for debugging Firefox itself
+devtools-commandkey-browser-console = J
+# Key pressed to toggle on the Responsive Design Mode
+devtools-commandkey-responsive-design-mode = M
+# Key pressed to open a toolbox with the inspector panel selected
+devtools-commandkey-inspector = C
+# Key pressed to open a toolbox with the web console panel selected
+devtools-commandkey-webconsole = K
+# Key pressed to open a toolbox with the debugger panel selected
+devtools-commandkey-jsdebugger = Z
+# Key pressed to open a toolbox with the network monitor panel selected
+devtools-commandkey-netmonitor = E
+# Key pressed to open a toolbox with the style editor panel selected
+devtools-commandkey-styleeditor = VK_F7
+# Key pressed to open a toolbox with the performance panel selected
+devtools-commandkey-performance = VK_F5
+# Key pressed to open a toolbox with the storage panel selected
+devtools-commandkey-storage = VK_F9
+# Key pressed to open a toolbox with the DOM panel selected
+devtools-commandkey-dom = W
+# Key pressed to open a toolbox with the accessibility panel selected
+devtools-commandkey-accessibility-f12 = VK_F12
+# Key pressed to start or stop the performance profiler
+devtools-commandkey-profiler-start-stop = VK_1
+# Key pressed to capture a recorded performance profile
+devtools-commandkey-profiler-capture = VK_2
+# Key pressed to toggle the JavaScript tracing
+devtools-commandkey-javascript-tracing-toggle = VK_5
diff --git a/thunderbird-l10n/cy/localization/cy/dom/XMLPrettyPrint.ftl b/thunderbird-l10n/cy/localization/cy/dom/XMLPrettyPrint.ftl
new file mode 100644
index 0000000000..4d753e10f5
--- /dev/null
+++ b/thunderbird-l10n/cy/localization/cy/dom/XMLPrettyPrint.ftl
@@ -0,0 +1,5 @@
+# This Source Code Form is subject to the terms of the Mozilla Public
+# License, v. 2.0. If a copy of the MPL was not distributed with this
+# file, You can obtain one at http://mozilla.org/MPL/2.0/.
+
+xml-nostylesheet = Does gan y ffeil XML yma ddim nodweddion steil yn perthyn iddi. Mae'r goeden ddogfen i'w weld isod.
diff --git a/thunderbird-l10n/cy/localization/cy/dom/media.ftl b/thunderbird-l10n/cy/localization/cy/dom/media.ftl
new file mode 100644
index 0000000000..21d348ce8d
--- /dev/null
+++ b/thunderbird-l10n/cy/localization/cy/dom/media.ftl
@@ -0,0 +1,6 @@
+# This Source Code Form is subject to the terms of the Mozilla Public
+# License, v. 2.0. If a copy of the MPL was not distributed with this
+# file, You can obtain one at http://mozilla.org/MPL/2.0/.
+
+default-audio-output-device-label = Dyfais allbwn sain rhagosodedig
+mediastatus-fallback-title = Mae { -brand-short-name } yn chwarae cyfryngau
diff --git a/thunderbird-l10n/cy/localization/cy/locales-preview/aboutTranslations.ftl b/thunderbird-l10n/cy/localization/cy/locales-preview/aboutTranslations.ftl
new file mode 100644
index 0000000000..68e9d8aafd
--- /dev/null
+++ b/thunderbird-l10n/cy/localization/cy/locales-preview/aboutTranslations.ftl
@@ -0,0 +1,28 @@
+# This Source Code Form is subject to the terms of the Mozilla Public
+# License, v. 2.0. If a copy of the MPL was not distributed with this
+# file, You can obtain one at http://mozilla.org/MPL/2.0/.
+
+# The title of the about:translations page, referencing the translations feature.
+about-translations-title = Translations
+about-translations-header = { -translations-brand-name }
+about-translations-results-placeholder = Translation
+# Text displayed on from-language dropdown when no language is selected
+about-translations-detect = Detect language
+# Text displayed on a language dropdown when the language is in beta
+# Variables:
+#   $language (string) - The localized display name of the language
+about-translations-displayname-beta = { $language } BETA
+# Text displayed on from-language dropdown when a language is detected
+# Variables:
+#   $language (string) - The localized display name of the detected language
+about-translations-detect-lang = Detect language ({ $language })
+# Text displayed on from-language dropdown when a beta language is detected
+# Variables:
+#   $language (string) - The localized display name of the detected language
+about-translations-detect-lang-beta = Detect language ({ $language } BETA)
+# Text displayed on to-language dropdown when no language is selected
+about-translations-select = Select language
+about-translations-textarea =
+  .placeholder = Add text to translate
+about-translations-no-support = Your device does not meet the minimum requirements to use this feature. Try on another device.
+about-translations-engine-error = The translations engine failed to load.
diff --git a/thunderbird-l10n/cy/localization/cy/messenger/about3Pane.ftl b/thunderbird-l10n/cy/localization/cy/messenger/about3Pane.ftl
new file mode 100644
index 0000000000..142fc5d277
--- /dev/null
+++ b/thunderbird-l10n/cy/localization/cy/messenger/about3Pane.ftl
@@ -0,0 +1,441 @@
+# This Source Code Form is subject to the terms of the Mozilla Public
+# License, v. 2.0. If a copy of the MPL was not distributed with this
+# file, You can obtain one at http://mozilla.org/MPL/2.0/.
+
+
+## Message List Header Bar
+
+quick-filter-button =
+    .title = Togglo'r Bar Hidlo Cyflym
+quick-filter-button-label = Hidl Cyflym
+thread-pane-header-display-button =
+    .title = Dewisiadau dangos rhestrau negeseuon
+# Variables:
+# $count (Number) - The number of messages in this folder.
+thread-pane-folder-message-count =
+    { $count ->
+        [zero] { $count } Neges
+        [one] { $count } Neges
+        [two] { $count } Neges
+        [few] { $count } Neges
+        [many] { $count } Neges
+       *[other] { $count } Neges
+    }
+# Variables:
+# $count (Number) - The number of messages currently selected.
+thread-pane-folder-selected-count =
+    { $count ->
+        [zero] { $count } Wedi'u dewis
+        [one] { $count } Wedi'i ddewis
+        [two] { $count } Wedi'u dewis
+        [few] { $count } Wedi'u dewis
+        [many] { $count } Wedi'u dewis
+       *[other] { $count } Wedi'u dewis
+    }
+thread-pane-header-context-table-view =
+    .label = Golwg Tabl
+thread-pane-header-context-cards-view =
+    .label = Golwg Cardiau
+thread-pane-header-context-hide =
+    .label = Cuddio Pennyn Rhestr Negeseuon
+
+## Quick Filter Bar
+
+# The tooltip to display when the user hovers over the sticky button
+# (currently displayed as a push-pin). When active, the sticky button
+# causes the current filter settings to be retained when the user changes
+# folders or opens new tabs. (When inactive, only the state of the text
+# filters are propagated between folder changes and when opening new tabs.)
+quick-filter-bar-sticky =
+    .title = Cadw hidlau ar waith wrth newid ffolderi
+# The tooltip for the filter button that replaces the quick filter buttons with
+# a dropdown menu.
+quick-filter-bar-dropdown =
+    .title = Dewislen hidlo cyflym
+quick-filter-bar-dropdown-unread =
+    .label = Heb eu Darllen
+quick-filter-bar-dropdown-starred =
+    .label = Serennog
+quick-filter-bar-dropdown-inaddrbook =
+    .label = Cysylltu
+quick-filter-bar-dropdown-tags =
+    .label = Tagiau
+quick-filter-bar-dropdown-attachment =
+    .label = Atodiad
+# The tooltip for the filter button that causes us to filter results to only
+# include unread messages.
+quick-filter-bar-unread =
+    .title = Dangos dim ond negeseuon heb eu darllen
+# The label for the filter button that causes us to filter results to only
+# include unread messages.
+quick-filter-bar-unread-label = Heb eu Darllen
+# The tooltip for the filter button that causes us to filter results to only
+# include messages that have been starred/flagged.
+quick-filter-bar-starred =
+    .title = Dangos dim ond negeseuon serennog
+# The label for the filter button that causes us to filter results to only
+# include messages that have been starred/flagged.
+quick-filter-bar-starred-label = Serennog
+# The tooltip for the filter button that causes us to filter results to only
+# include messages from contacts in one of the user's non-remote address
+# books.
+quick-filter-bar-inaddrbook =
+    .title = Dangos dim ond negeseuon gan bobl yn eich llyfr cyfeiriadau
+# The label for the filter button that causes us to filter results to only
+# include messages from contacts in one of the user's non-remote address
+# books.
+quick-filter-bar-inaddrbook-label = Cysylltiad
+# The tooltip for the filter button that causes us to filter results to only
+# include messages with at least one tag on them.
+quick-filter-bar-tags =
+    .title = Dangos dim ond negeseuon gyda thagiau
+# The label for the filter button that causes us to filter results to only
+# include messages with at least one tag on them.
+quick-filter-bar-tags-label = Tagiau
+# The tooltip for the filter button that causes us to filter results to only
+# include messages with attachments.
+quick-filter-bar-attachment =
+    .title = Dangos dim ond negeseuon gydag atodiadau
+# The label for the filter button that causes us to filter results to only
+# include messages with attachments.
+quick-filter-bar-attachment-label = Atodiad
+# The contents of the results box when there is a filter active but there
+# are no messages matching the filter.
+quick-filter-bar-no-results = Dim canlyniadau
+# This is used to populate the results box; it either displays the
+# number of messages found using this string, that there are no messages
+# (using quick-filter-bar-no-results), or the box is hidden.
+# Variables:
+# $count (Number) - The number of messages that match selected filters.
+quick-filter-bar-results =
+    { $count ->
+        [zero] Dim negeseuon
+        [one] { $count } neges
+        [two] { $count } neges
+        [few] { $count } neges
+        [many] { $count } neges
+       *[other] { $count } neges
+    }
+# Keyboard shortcut for the text search box.
+# This should match quick-filter-bar-show in messenger.ftl.
+quick-filter-bar-textbox-shortcut =
+    { PLATFORM() ->
+        [macos] ⇧ ⌘ K
+       *[other] Ctrl+Shift+K
+    }
+# This is the empty text for the text search box.
+# The goal is to convey to the user that typing in the box will filter
+# the messages and that there is a hotkey they can press to get to the
+# box faster.
+quick-filter-bar-textbox =
+    .placeholder = Hidlo'r negeseuon hyn <{ quick-filter-bar-textbox-shortcut }>
+quick-filter-bar-search =
+    .label = Hidlo negeseuon:
+# Keyboard shortcut for the text search box.
+# This should match quick-filter-bar-show in messenger.ftl.
+quick-filter-bar-search-shortcut =
+    { PLATFORM() ->
+        [macos] <kbd>⇧</kbd> <kbd>⌘</kbd> <kbd>K</kbd>
+       *[other] <kbd>Ctrl</kbd> + <kbd>Shift</kbd> + <kbd>K</kbd>
+    }
+# This is the empty text for the text search box.
+# The goal is to convey to the user that typing in the box will filter the
+# messages and that there is a hotkey they can press to get to the box faster.
+quick-filter-bar-search-placeholder-with-key = Hidlo negeseuon… { quick-filter-bar-search-shortcut }
+# Label of the search button in the quick filter bar text box. Clicking it will
+# launch a global search.
+quick-filter-bar-search-button =
+    .alt = Chwilio ym mhobman
+# Tooltip of the Any-of/All-of tagging mode selector.
+quick-filter-bar-boolean-mode =
+    .title = Modd hidlo tagiau
+# The Any-of tagging mode.
+quick-filter-bar-boolean-mode-any =
+    .label = Unrhyw un o
+    .title = Dylai o leiaf un o'r meini prawf tag hyn gydweddu
+# The All-of tagging mode.
+quick-filter-bar-boolean-mode-all =
+    .label = Pob un
+    .title = Dylai pob un o'r meini prawf tag hyn gydweddu
+# This label explains what the sender/recipients/subject/body buttons do.
+# This string should ideally be kept short because the label and the text
+# filter buttons share their bar (that appears when there is text in the text
+# filter box) with the list of tags when the tag filter is active, and the
+# tag sub-bar wants as much space as possible. (Overflow is handled by an
+# arrow scroll box.)
+quick-filter-bar-text-filter-explanation = Hidlo negeseuon yn ôl:
+# The button label that toggles whether the text filter searches the message
+# sender for the string.
+quick-filter-bar-text-filter-sender = Anfonwr
+# The button label that toggles whether the text filter searches the message
+# recipients (to, cc) for the string.
+quick-filter-bar-text-filter-recipients = Derbynwyr
+# The button label that toggles whether the text filter searches the message
+# subject for the string.
+quick-filter-bar-text-filter-subject = Pwnc
+# The button label that toggles whether the text filter searches the message
+# body for the string.
+quick-filter-bar-text-filter-body = Corff
+# The first line of the panel popup that tells the user we found no matches
+# but we can convert to a global search for them.
+quick-filter-bar-gloda-upsell-line1 = Parhau i chwilio pob ffolder
+# The second line of the panel popup that tells the user we found no matches.
+# Variables:
+# $text (String) - What the user has typed so far.
+quick-filter-bar-gloda-upsell-line2 = Pwyswch ‘Enter’ eto i barhau i chwilio am: { $text }
+
+## Folder pane
+
+folder-pane-get-messages-button =
+    .title = Estyn Negeseuon
+folder-pane-get-all-messages-menuitem =
+    .label = Estyn Pob Neges Newydd
+    .accesskey = E
+folder-pane-write-message-button = Neges Newydd
+    .title = Ysgrifennu neges newydd
+folder-pane-more-menu-button =
+    .title = Dewisiadau paen ffolder
+# Context menu item to show/hide different folder types in the folder pane
+folder-pane-header-folder-modes =
+    .label = Moddau ffolder
+# Context menu item to toggle display of "Get messages" button in folder pane header
+folder-pane-header-context-toggle-get-messages =
+    .label = Dangos “Cael negeseuon”
+# Context menu item to toggle display of "New Message" button in folder pane header
+folder-pane-header-context-toggle-new-message =
+    .label = Dangos “Neges Newydd”
+folder-pane-header-context-hide =
+    .label = Cuddio Penyn Paen Ffolder
+folder-pane-show-total-toggle =
+    .label = Dangos Cyfanswm Nifer y Negeseuon
+# Context menu item to show or hide folder sizes
+folder-pane-header-toggle-folder-size =
+    .label = Dangos Maint Ffolder
+folder-pane-header-hide-local-folders =
+    .label = Cuddio Ffolderi Lleol
+folder-pane-mode-context-button =
+    .title = Dewisiadau modd ffolder
+folder-pane-mode-context-toggle-compact-mode =
+    .label = Golwg Cryno
+    .accesskey = G
+folder-pane-mode-move-up =
+    .label = Symud i Fyny
+folder-pane-mode-move-down =
+    .label = Symud i Lawr
+# Variables:
+# $count (Number) - Number of unread messages.
+folder-pane-unread-aria-label =
+    { $count ->
+        [zero] { $count } neges heb eu darllen
+        [one] 1 neges heb ei darllen
+        [two] { $count } neges heb eu darllen
+        [few] { $count } neges heb eu darllen
+        [many] { $count } neges heb eu darllen
+       *[other] { $count } neges heb eu darllen
+    }
+# Variables:
+# $count (Number) - Number of total messages.
+folder-pane-total-aria-label =
+    { $count ->
+        [zero] Cyfanswm o { $count } neges
+        [one] Cyfamswm o 1 neges
+        [two] Cyfanswm o { $count } neges
+        [few] Cyfanswm o { $count } neges
+        [many] Cyfanswm o { $count } neges
+       *[other] Cyfanswm o { $count } neges
+    }
+
+## Message thread pane
+
+threadpane-column-header-select =
+    .title = Newid dewis pob neges
+threadpane-column-header-select-all =
+    .title = Dewis pob neges
+threadpane-column-header-deselect-all =
+    .title = Dad-ddewis pob neges
+threadpane-column-label-select =
+    .label = Dewis Negeseuon
+threadpane-cell-select =
+    .aria-label = Dewiswch neges
+threadpane-column-header-thread =
+    .title = Newid edafedd negeseuon
+threadpane-column-label-thread =
+    .label = Edefyn
+threadpane-cell-thread =
+    .aria-label = Statws trywydd
+threadpane-column-header-flagged =
+    .title = Trefnu yn ôl sêr
+threadpane-column-label-flagged =
+    .label = Serennog
+threadpane-cell-flagged =
+    .aria-label = Serennog
+threadpane-flagged-cell-label = Serennog
+threadpane-column-header-attachments =
+    .title = Trefnu yn ôl atodiad
+threadpane-column-label-attachments =
+    .label = Atodiadau
+threadpane-cell-attachments =
+    .aria-label = Atodiadau
+threadpane-attachments-cell-label = Atodiadau
+threadpane-column-header-spam =
+    .title = Trefnu yn ôl statws sbam
+threadpane-column-label-spam =
+    .label = Sbam
+threadpane-cell-spam =
+    .aria-label = Statws sbam
+threadpane-spam-cell-label = Sbam
+threadpane-column-header-unread-button =
+    .title = Trefnu yn ôl statws darllen
+threadpane-column-label-unread-button =
+    .label = Statws darllen
+threadpane-cell-read-status =
+    .aria-label = Statws darllen
+threadpane-read-cell-label = Darllenwyd
+threadpane-unread-cell-label = Heb eu Darllen
+threadpane-column-header-sender = Oddi wrth
+    .title = Trefnu yn ôl anfonwr
+threadpane-column-label-sender =
+    .label = Oddi wrth
+threadpane-cell-sender =
+    .aria-label = Oddi wrth
+threadpane-column-header-recipient = Derbynnydd
+    .title = Trefnu yn ôl derbyniwr
+threadpane-column-label-recipient =
+    .label = Derbynnydd
+threadpane-cell-recipient =
+    .aria-label = Derbynnydd
+threadpane-column-header-correspondents = Cyfathrebwyr
+    .title = Trefnu yn ôl cyfathrebwyr
+threadpane-column-label-correspondents =
+    .label = Cyfathrebwyr
+threadpane-cell-correspondents =
+    .aria-label = Cyfathrebwyr
+threadpane-column-header-subject = Pwnc
+    .title = Trefnu yn ôl pwnc
+threadpane-column-label-subject =
+    .label = Pwnc
+threadpane-cell-subject =
+    .aria-label = Pwnc
+threadpane-column-header-date = Dyddiad
+    .title = Trefnu yn ôl dyddiad
+threadpane-column-label-date =
+    .label = Dyddiad
+threadpane-cell-date =
+    .aria-label = Dyddiad
+threadpane-column-header-received = Derbyniwyd
+    .title = Trefnu yn ôl dyddiad derbyniwyd
+threadpane-column-label-received =
+    .label = Derbyniwyd
+threadpane-cell-received =
+    .aria-label = Dyddiad derbyn
+threadpane-column-header-status = Statws
+    .title = Trefnu yn ôl statws
+threadpane-column-label-status =
+    .label = Statws
+threadpane-cell-status =
+    .aria-label = Statws
+threadpane-column-header-size = Maint
+    .title = Trefnu yn ôl maint
+threadpane-column-label-size =
+    .label = Maint
+threadpane-cell-size =
+    .aria-label = Maint
+threadpane-column-header-tags = Tag
+    .title = Trefnu yn ôl tagiau
+threadpane-column-label-tags =
+    .label = Tag
+threadpane-cell-tags =
+    .aria-label = Tagiau
+threadpane-column-header-account = Cyfrif
+    .title = Trefnu yn ôl cyfrif
+threadpane-column-label-account =
+    .label = Cyfrif
+threadpane-cell-account =
+    .aria-label = Cyfrif
+threadpane-column-header-priority = Blaenoriaeth
+    .title = Trefnu yn ôl blaenoriaeth
+threadpane-column-label-priority =
+    .label = Blaenoriaeth
+threadpane-cell-priority =
+    .aria-label = Blaenoriaeth
+threadpane-column-header-unread = Heb eu Darllen
+    .title = Nifer y negeseuon heb eu darllen yn yr edafedd
+threadpane-column-label-unread =
+    .label = Heb eu Darllen
+threadpane-cell-unread =
+    .aria-label = Nifer y negeseuon heb eu darllen
+threadpane-column-header-total = Cyfanswm
+    .title = Cyfanswm y nifer o negeseuon yn yr edafedd
+threadpane-column-label-total =
+    .label = Cyfanswm
+threadpane-cell-total =
+    .aria-label = Cyfanswm nifer y negeseuon
+threadpane-column-header-location = Lleoliad
+    .title = Trefnu yn ôl lleoliad
+threadpane-column-label-location =
+    .label = Lleoliad
+threadpane-cell-location =
+    .aria-label = Lleoliad
+threadpane-column-header-id = Trefn Derbyn
+    .title = Trefnu yn ôl y drefn derbyniwyd
+threadpane-column-label-id =
+    .label = Trefn Derbyn
+threadpane-cell-id =
+    .aria-label = Derbyniwyd archeb
+threadpane-column-header-delete =
+    .title = Dileu neges
+threadpane-column-label-delete =
+    .label = Dileu
+threadpane-cell-delete =
+    .aria-label = Dileu
+
+## Message state variations
+
+threadpane-message-new =
+    .alt = Dangosydd neges newydd
+    .title = Neges newydd
+threadpane-message-replied =
+    .alt = Dangosydd ateb
+    .title = Wedi ateb y neges
+threadpane-message-redirected =
+    .alt = Dangosydd ailgyfeirio
+    .title = Wedi ailgyfeirio'r neges
+threadpane-message-forwarded =
+    .alt = Dangosydd anfon ymlaen
+    .title = Neges wedi'i anfon ymlaen
+threadpane-message-replied-forwarded =
+    .alt = Dangosydd ateb ac anfon
+    .title = Dangosydd wedi ateb ac anfon
+threadpane-message-replied-redirected =
+    .alt = Dangosydd ateb ac ailgyfeirio
+    .title = Neges wedi'i hateb a'i hailgyfeirio
+threadpane-message-forwarded-redirected =
+    .alt = Dangosydd anfon ymlaen ac ailgyfeirio
+    .title = Neges wedi'i hanfon ymlaen a'i hailgyfeirio
+threadpane-message-replied-forwarded-redirected =
+    .alt = Dangosydd ateb, anfon ymlaen ac ailgyfeirio
+    .title = Wedi ateb, anfon ymlaen, ac ailgyfeirio'r neges
+apply-columns-to-menu =
+    .label = Gosod y colofnau yn y…
+apply-current-view-to-menu =
+    .label = Gosod yr olwg gyfredol i…
+apply-current-view-to-folder =
+    .label = Ffolder…
+apply-current-view-to-folder-children =
+    .label = Ffolder a'i blant…
+
+## Apply columns confirmation dialog
+
+apply-changes-to-folder-title = Gosod y Newidiadau?
+# Variables:
+#  $name (String): The name of the folder to apply to.
+apply-current-columns-to-folder-message = Gosod colofnau cyfredol y ffolder i { $name }?
+# Variables:
+#  $name (String): The name of the folder to apply to.
+apply-current-columns-to-folder-with-children-message = Gosod colofnau'r ffolder gyfredol i { $name } a'i blant?
+# Variables:
+#  $name (String): The name of the folder to apply to.
+apply-current-view-to-folder-message = Gosod golwg y ffolder gyfredol i { $name }?
+# Variables:
+#  $name (String): The name of the folder to apply to.
+apply-current-view-to-folder-with-children-message = Gosod golwg y ffolder gyfredol i { $name } a'i phlant?
diff --git a/thunderbird-l10n/cy/localization/cy/messenger/aboutAddonsExtra.ftl b/thunderbird-l10n/cy/localization/cy/messenger/aboutAddonsExtra.ftl
new file mode 100644
index 0000000000..9723028e4d
--- /dev/null
+++ b/thunderbird-l10n/cy/localization/cy/messenger/aboutAddonsExtra.ftl
@@ -0,0 +1,12 @@
+# This Source Code Form is subject to the terms of the Mozilla Public
+# License, v. 2.0. If a copy of the MPL was not distributed with this
+# file, You can obtain one at http://mozilla.org/MPL/2.0/.
+
+add-on-options-button =
+    .title = Dewisiadau Ychwanegion
+
+add-on-search-alternative-button-label = Canfod ychwanegyn arall
+
+atn-addons-heading-search-input =
+    .placeholder = Chwilio addons.thunderbird.net
+
diff --git a/thunderbird-l10n/cy/localization/cy/messenger/aboutDialog.ftl b/thunderbird-l10n/cy/localization/cy/messenger/aboutDialog.ftl
new file mode 100644
index 0000000000..131ce3e312
--- /dev/null
+++ b/thunderbird-l10n/cy/localization/cy/messenger/aboutDialog.ftl
@@ -0,0 +1,66 @@
+# This Source Code Form is subject to the terms of the Mozilla Public
+# License, v. 2.0. If a copy of the MPL was not distributed with this
+# file, You can obtain one at http://mozilla.org/MPL/2.0/.
+
+about-update-whats-new = Be sy'n Newydd
+aboutDialog-title =
+    .title = Ynghylch { -brand-full-name }
+about-dialog-title = Ynghylch { -brand-full-name }
+release-notes-link = Nodiadau ryddhau
+update-internal-error = Methu gwirio am ddiweddariadau oherwydd gwall mewnol. Diweddariadau ar gael yn <a data-l10n-name="manual-link">
+update-check-for-updates-button = Gwirio am Ddiweddariadau
+    .accesskey = D
+update-update-button = Ailgychwyn i ddiweddaru { -brand-shorter-name }
+    .accesskey = A
+update-checking-for-updates = Gwirio am ddiweddariadau…
+update-downloading-message = Llwytho'r diweddariad i lawr - <span data-l10n-name="download-status"></span>
+update-applying = Gosod y diweddariad…
+update-downloading = <img data-l10n-name="icon"/>Llwytho'r diweddariad i lawr - <span data-l10n-name="download-status"></hspan>
+update-failed = Methodd y diweddaru. <a data-l10n-name="failed-link">Llwytho'r fersiwn diweddaraf i lawr</a>
+update-admin-disabled = Mae'r diweddariad wedi'i analluogi gan eich gweinyddwr
+update-no-updates-found = Mae { -brand-short-name } yn gyfredol
+update-other-instance-handling-updates = Mae { -brand-short-name } yn cael ei ddiweddaru gan enghraifft arall
+update-manual = Diweddariadau ar gael yn <a data-l10n-name="manual-link">
+update-unsupported = Nid oes modd i chi ddiweddaru'r system hwn ymhellach. <a data-l10n-name="unsupported-link">Dysgu rhagor</a>
+update-restarting = Ailgychwyn…
+# Variables:
+#   $channel (String): description of the update channel (e.g. "release", "beta", "nightly" etc.)
+channel-description = Rydych ar sianel diweddaru <span data-l10n-name="current-channel">{ $channel }</span> .
+warning-desc-version = Mae { -brand-short-name } yn arbrofol a gall fod yn ansad.
+warning-desc-telemetry = Mae'n anfon gwybodaeth yn awtomatig am berfformiad, caledwedd, defnydd a chyfaddasu nôl i { -vendor-short-name } i helpu i wneud { -brand-short-name } yn well.
+# Example of resulting string: 66.0.1 (64-bit)
+# Variables:
+#   $version (String): version of Thunderbird, e.g. 66.0.1
+#   $bits (Number): bits of the architecture (32 or 64)
+aboutDialog-version = { $version } ({ $bits }-did)
+# Example of resulting string: 66.0a1 (2019-01-16) (64-bit)
+# Variables:
+#   $version (String): version of Thunderbird for Daily builds, e.g. 66.0a1
+#   $isodate (String): date in ISO format, e.g. 2019-01-16
+#   $bits (Number): bits of the architecture (32 or 64)
+aboutDialog-version-nightly = { $version } ({ $isodate }) ({ $bits }-did)
+aboutdialog-update-checking-failed = Wedi methu â gwirio am ddiweddariadau.
+community-exp =
+    <a data-l10n-name="community-exp-mozilla-link">
+    Mae { -vendor-short-name }</a>
+     yn <a data-l10n-name="community-exp-credits-link">
+    gymuned fyd-eang</a>
+     sy'n cydweithio i gadw'r We yn agored, cyhoeddus ac ar gael i bawb.
+community-2 =
+    Cynlluniwyd { -brand-short-name } gan <a data-l10n-name="community-mozilla-link">
+    { -vendor-short-name }</a>
+    , a <a data-l10n-name="community-credits-link">
+    chymuned fyd-eang</a>
+     sy'n cydweithio i gadw'r We yn agored, cyhoeddus ac ar gael i bawb.
+about-helpus =
+    Hoffech chi helpu? <a data-l10n-name="helpus-donate-link">
+    Gwnewch gyfraniad</a> or <a data-l10n-name="helpus-get-involved-link">
+    beth am ymuno â ni!</a>
+community-experimental = <a data-l10n-name="community-exp-mozilla-link">Mae { -vendor-short-name }</a> yn <a data-l10n-name="community-exp-credits-link">gymuned fyd-eang</a> sy'n cydweithio i gadw'r We yn agored, cyhoeddus ac ar gael i bawb.
+community-desc = Cynlluniwyd { -brand-short-name } gan <a data-l10n-name="community-mozilla-link">{ -vendor-short-name }</a>, a <a data-l10n-name="community-credits-link">chymuned fyd-eang</a> sy'n cydweithio i gadw'r We yn agored, cyhoeddus ac ar gael i bawb.
+about-donation = Hoffech chi helpu? <a data-l10n-name="helpus-donate-link">Gwnewch gyfraniad</a> or <a data-l10n-name="helpus-get-involved-link">beth am ymuno â ni!</a>
+bottom-links-license = Manylion Trwyddedu
+bottom-links-rights = Hawliau'r Defnyddiwr
+bottom-links-privacy = Polisi Preifatrwydd
+cmd-close-mac-command-key =
+    .key = w
diff --git a/thunderbird-l10n/cy/localization/cy/messenger/aboutImport.ftl b/thunderbird-l10n/cy/localization/cy/messenger/aboutImport.ftl
new file mode 100644
index 0000000000..7b1526d2a9
--- /dev/null
+++ b/thunderbird-l10n/cy/localization/cy/messenger/aboutImport.ftl
@@ -0,0 +1,287 @@
+# This Source Code Form is subject to the terms of the Mozilla Public
+# License, v. 2.0. If a copy of the MPL was not distributed with this
+# file, you can obtain one at http://mozilla.org/MPL/2.0/.
+
+import-page-title = Mewnforio
+
+export-page-title = Allforio
+
+## Header
+
+import-start = Teclyn Mewnforio
+
+import-start-title = Mewnforio gosodiadau neu ddata o raglen neu ffeil.
+
+import-start-description = Dewiswch y ffynhonnell rydych chi am fewnforio ohoni. Yn ddiweddarach, byddwn yn gofyn i chi ddewis pa ddata sydd angen ei fewnforio.
+
+import-from-app = Mewnforio o'r Rhaglen
+
+import-file = Mewnforio o ffeil
+
+import-file-title = Dewiswch ffeil i fewnforio ei chynnwys.
+
+import-file-description = Dewiswch fewnforio proffil, llyfrau cyfeiriadau neu galendrau sydd wedi'u cadw wrth gefn yn  flaenorol.
+
+import-address-book-title = Mewnforio ffeil Llyfr Cyfeiriadau
+
+import-calendar-title = Mewnforio ffeil Calendr
+
+export-profile = Allforio
+
+## Buttons
+
+button-back = Nôl
+
+button-continue = Parhau
+
+button-export = Allforio
+
+button-finish = Gorffen
+
+## Import from app steps
+
+app-name-thunderbird = Thunderbird
+
+app-name-seamonkey = SeaMonkey
+
+app-name-outlook = Outlook
+
+app-name-becky = Becky! Internet Mail
+
+app-name-apple-mail = Apple Mail
+
+source-thunderbird = Mewnforio o osodiad { app-name-thunderbird } arall
+
+source-thunderbird-description = Mewnforio gosodiadau, hidlwyr, negeseuon, a data arall o broffil { app-name-thunderbird }.
+
+source-seamonkey = Mewnforio o osodiad { app-name-seamonkey }
+
+source-seamonkey-description = Mewnforio gosodiadau, hidlwyr, negeseuon, a data arall o broffil { app-name-seamonkey }.
+
+source-outlook = Mewnforio o { app-name-outlook }
+
+source-outlook-description = Mewnforio cyfrifon, llyfrau cyfeiriadau, a negeseuon o { app-name-outlook }.
+
+source-becky = Mewnforio o { app-name-becky }
+
+source-becky-description = Mewnforio llyfrau cyfeiriadau a negeseuon o { app-name-becky }.
+
+source-apple-mail = Mewnforio o { app-name-apple-mail }
+
+source-apple-mail-description = Mewnforio negeseuon o { app-name-apple-mail }.
+
+source-file2 = Mewnforio o ffeil
+
+source-file-description = Dewiswch ffeil i fewnforio llyfrau cyfeiriadau, calendrau, neu gopi wrth gefn o broffil (ffeil ZIP).
+
+## Import from file selections
+
+file-profile2 = Mewnforio Proffil Wrth Gefn
+
+file-profile-description = Dewiswch broffil Thunderbird sydd wedi'i gadw wrth gefn yn flaenorol (.zip)
+
+file-calendar = Mewnforio Calendrau
+
+file-calendar-description = Dewiswch ffeil sy'n cynnwys Calendrau neu Ddigwyddiadau wedi'u hallforio (.ics)
+
+file-addressbook = Mewnforio Llyfrau Cyfeiriadau
+
+file-addressbook-description = Dewiswch ffeil sy'n cynnwys Llyfrau Cyfeiriadau a Chysylltiadau wedi'u hallforio
+
+## Import from app profile steps
+
+from-app-thunderbird = Mewnforio o broffil { app-name-thunderbird }
+
+from-app-seamonkey = Mewnforio o broffil { app-name-seamonkey }
+
+from-app-outlook = Mewnforio o { app-name-outlook }
+
+from-app-becky = Mewnforio o { app-name-becky }
+
+from-app-apple-mail = Mewnforio o { app-name-apple-mail }
+
+profiles-pane-title-thunderbird = Mewnforio Gosodiadau a Data o broffil { app-name-thunderbird }.
+
+profiles-pane-title-seamonkey = Mewnforio Gosodiadau a Data o broffil { app-name-seamonkey }.
+
+profiles-pane-title-outlook = Mewnforio Data o { app-name-outlook }.
+
+profiles-pane-title-becky = Mewnforio Data o { app-name-becky }.
+
+profiles-pane-title-apple-mail = Mewnforio Negeseuon o { app-name-apple-mail }.
+
+profile-source = Mewnforio o broffil
+
+# $profileName (string) - name of the profile
+profile-source-named = Mewnforio o'r proffil <strong>"{ $profileName }"</strong>
+
+profile-file-picker-directory = Dewiswch ffolder proffil
+
+profile-file-picker-archive = Dewiswch ffeil <strong>ZIP</strong>
+
+profile-file-picker-archive-description = Rhaid i'r ffeil ZIP fod yn llai na 2GB.
+
+profile-file-picker-archive-title = Dewiswch ffeil ZIP (llai na 2GB)
+
+items-pane-title2 = Dewiswch beth i'w fewnforio:
+
+items-pane-directory = Cyfeiriadur:
+
+items-pane-profile-name = Enw proffil:
+
+items-pane-checkbox-accounts = Cyfrifon a Gosodiadau
+
+items-pane-checkbox-address-books = Llyfrau Cyfeiriadau
+
+items-pane-checkbox-calendars = Calendrau
+
+items-pane-checkbox-mail-messages = Negeseuon E-bost
+
+items-pane-override = Ni fydd unrhyw ddata presennol neu'r un fath yn cael ei drosysgrifo.
+
+## Import from address book file steps
+
+import-from-addr-book-file-description = Dewiswch y fformat ffeil sy'n cynnwys eich data Llyfr Cyfeiriadau.
+
+addr-book-csv-file = Ffeil wedi'i gwahanu gan goma neu dab (.csv, .tsv)
+
+addr-book-ldif-file = Ffeil LDIF (.ldif)
+
+addr-book-vcard-file = Ffeil vCard (.vcf, .vcard)
+
+addr-book-sqlite-file = Ffeil cronfa ddata SQLite (.sqlite)
+
+addr-book-mab-file = Ffeil cronfa ddata Mork (.mab)
+
+addr-book-file-picker = Dewiswch ffeil llyfr cyfeiriadau
+
+addr-book-csv-field-map-title = Cydweddu enwau meysydd
+
+addr-book-csv-field-map-desc = Dewiswch feysydd llyfr cyfeiriadau sy'n cyfateb i'r meysydd ffynhonnell. Dad-diciwch y meysydd nad ydych am eu mewnforio.
+
+addr-book-directories-title = Dewiswch o ble i fewnforio'r data a ddewiswyd
+
+addr-book-directories-pane-source = Ffeil ffynhonnell:
+
+# $addressBookName (string) - name of the new address book that would be created.
+addr-book-import-into-new-directory2 = Crëwch gyfeiriadur newydd o'r enw <strong>"{ $addressBookName }"</strong>
+
+# $addressBookName (string) - name of the address book to import into
+addr-book-summary-title = Mewnforio'r data a ddewiswyd i'r cyfeiriadur " { $addressBookName } "
+
+# $addressBookName (string) - name of the address book that will be created.
+addr-book-summary-description = Bydd llyfr cyfeiriadau newydd o'r enw " { $addressBookName } " yn cael ei greu.
+
+## Import from calendar file steps
+
+import-from-calendar-file-desc = Dewiswch y ffeil iCalendar (.ics) yr hoffech ei mewnforio.
+
+calendar-items-title = Dewiswch pa eitemau i'w mewnforio.
+
+calendar-items-loading = Wrthi'n llwytho eitemau…
+
+calendar-items-filter-input =
+    .placeholder = Hidlo eitemau…
+
+calendar-select-all-items = Dewis y cyfan
+
+calendar-deselect-all-items = Dad-ddewis y cyfan
+
+calendar-target-title = Dewiswch ble i fewnforio'r eitemau a ddewiswyd.
+
+# $targetCalendar (string) - name of the new calendar that would be created
+calendar-import-into-new-calendar2 = Crëwch galendr newydd o'r enw <strong>"{ $targetCalendar }"</strong>
+
+# $itemCount (number) - count of selected items (tasks, events) that will be imported
+# $targetCalendar (string) - name of the calendar the items will be imported into
+calendar-summary-title =
+    { $itemCount ->
+        [zero] Mewnforio { $itemCount } eitem i'r calendr " { $targetCalendar } "
+        [one] Mewnforio un eitem i'r calendr " { $targetCalendar } "
+        [two] Mewnforio { $itemCount } eitem i'r calendr " { $targetCalendar } "
+        [few] Mewnforio { $itemCount } eitem i'r calendr " { $targetCalendar } "
+        [many] Mewnforio { $itemCount } eitem i'r calendr " { $targetCalendar } "
+       *[other] Mewnforio { $itemCount } eitem i'r calendr " { $targetCalendar } "
+    }
+
+# $targetCalendar (string) - name of the calendar that will be created
+calendar-summary-description = Bydd calendr newydd o'r enw " { $targetCalendar } " yn cael ei greu.
+
+## Import dialog
+
+# $progressPercent (string) - percent formatted progress (for example "10%")
+progress-pane-importing2 = Wrthi'n mewnforio… { $progressPercent }
+
+# $progressPercent (string) - percent formatted progress (for example "10%")
+progress-pane-exporting2 = Wrthi'n allforio… { $progressPercent }
+
+progress-pane-finished-desc2 = Gorffen.
+
+error-pane-title = Gwall
+
+error-message-zip-file-too-big2 = Mae'r ffeil zip a ddewiswyd yn fwy na 2GB. Echdynnwch hi'n gyntaf, yna ei mewnforio o'r ffolder cafodd ei hechdynnu.
+
+error-message-extract-zip-file-failed2 = Wedi methu echdynnu'r ffeil zip. Echdynwch hi â llaw, yna ei mewnforio o'r ffolder wedi'i hechdynnu yn lle hynny.
+
+error-message-failed = Methodd y mewnforio yn annisgwyl, efallai y bydd mwy o wybodaeth ar gael yn y Consol Gwallau.
+
+error-failed-to-parse-ics-file = Heb ganfod unrhyw eitemau i'w mewnforio yn y ffeil.
+
+error-export-failed = Methodd y mewnforio yn annisgwyl, efallai y bydd rhagor o wybodaeth ar gael yn y Consol Gwallau.
+
+error-message-no-profile = Heb ganfod proffil.
+
+## <csv-field-map> element
+
+csv-first-row-contains-headers = Mae'r rhes gyntaf yn cynnwys enwau meysydd
+
+csv-source-field = Maes ffynhonnell
+
+csv-source-first-record = Cofnod cyntaf
+
+csv-source-second-record = Ail gofnod
+
+csv-target-field = Maes llyfr cyfeiriadau
+
+## Export tab
+
+export-profile-title = Allforiwch gyfrifon, negeseuon, llyfrau cyfeiriadau, a gosodiadau i ffeil ZIP.
+
+export-profile-description = Os yw eich proffil presennol yn fwy na 2GB, rydym yn awgrymu eich bod yn gwneud copi wrth gefn ohono ar eich cyfer chi eich hun.
+
+export-open-profile-folder = Agor ffolder proffil
+
+export-file-picker2 = Allforio i ffeil ZIP
+
+export-brand-name = { -brand-product-name }
+
+## Summary pane
+
+summary-pane-title = Data i'w fewnforio
+
+summary-pane-start = Cychwyn Mewnforio
+
+summary-pane-warning = Bydd angen ailgychwyn { -brand-product-name } pan fydd y mewnforio wedi'i gwblhau.
+
+summary-pane-start-over = Ailgychwyn y Teclyn Mewnforio
+
+## Footer area
+
+footer-help = Angen cymorth?
+
+footer-import-documentation = Dogfennaeth gosod
+
+footer-export-documentation = Dogfennaeth allforio
+
+footer-support-forum = Fforwm cefnogi
+
+## Step navigation on top of the wizard pages
+
+step-list =
+    .aria-label = Camau mewnforio
+
+step-confirm = Cadarnhau
+
+# Variables:
+# $number (number) - step number
+step-count = { $number }
diff --git a/thunderbird-l10n/cy/localization/cy/messenger/aboutProfilesExtra.ftl b/thunderbird-l10n/cy/localization/cy/messenger/aboutProfilesExtra.ftl
new file mode 100644
index 0000000000..365a877011
--- /dev/null
+++ b/thunderbird-l10n/cy/localization/cy/messenger/aboutProfilesExtra.ftl
@@ -0,0 +1,5 @@
+# This Source Code Form is subject to the terms of the Mozilla Public
+# License, v. 2.0. If a copy of the MPL was not distributed with this
+# file, You can obtain one at http://mozilla.org/MPL/2.0/.
+
+profiles-launch-profile-plain = Agor proffil
diff --git a/thunderbird-l10n/cy/localization/cy/messenger/aboutRights.ftl b/thunderbird-l10n/cy/localization/cy/messenger/aboutRights.ftl
new file mode 100644
index 0000000000..0d99e1fdcd
--- /dev/null
+++ b/thunderbird-l10n/cy/localization/cy/messenger/aboutRights.ftl
@@ -0,0 +1,30 @@
+# This Source Code Form is subject to the terms of the Mozilla Public
+# License, v. 2.0. If a copy of the MPL was not distributed with this
+# file, You can obtain one at http://mozilla.org/MPL/2.0/.
+
+rights-title = Ynghylch eich hawliau
+rights-intro = Mae { -brand-full-name } yn feddalwedd cod agored rhydd a rhad, wedi ei adeiladu gan gymuned o filoedd o bobl ar draws y byd i gyd. Mae yna rhai pethau i chi gael gwybod:
+rights-intro-point-1 = Mae { -brand-short-name } ar gael i chi o dan amodau'r <a data-l10n-name="mozilla-public-license-link">Trwydded Gyhoeddus Mozilla</a>. Mae hyn yn golygu y cewch ddefnyddio, gopïo a dosbarthu { -brand-short-name } i eraill.  Mae croeso i chi newid cod ffynhonnell { -brand-short-name } yn ôl eich angen. Mae Trwydded Gyhoeddus Mozilla yn rhoi'r hawl i chi ddosbarthu'r fersiwn rydych wedi ei newid.
+rights-intro-point-2 = Nid ydych yn derbyn unrhyw hawliau nod masnachu na thrwyddedau i nod masnach y Mozilla Foundation neu unrhyw barti, gan gynnwys heb gyfyngiadau i enw na logo Thunderbird . Mae gwybodaeth bellach am nodau masnach i’w cael <a data-l10n-name="mozilla-trademarks-link">yma</a>.
+rights-intro-point-3 = Mae rhai nodweddion yn { -brand-short-name }, megis yr Adroddwr Chwalu, yn rhoi'r dewis i chi gyfrannu adborth i { -vendor-short-name }. Drwy ddewis cyflwyno adborth rydych yn rhoi i { -vendor-short-name } ganiatâd i ddefnyddio'r adborth i wella ei gynnyrch, i gyhoeddi'r adborth ar ei wefannau, ac i ddosbarthu'r adborth.
+rights-intro-point-4 = Mae sut rydym yn defnyddio y data personol ac adborth rydych wedi ei gyflwyno i { -vendor-short-name } drwy { -brand-short-name } yn cael ei ddisgrifio yn <a data-l10n-name="mozilla-privacy-policy-link">Polisi Preifatrwydd { -brand-short-name }</a>.
+rights-intro-point-4-unbranded = Rhaid rhestri unrhyw bolisïau preifatrwydd perthnasol yma.
+rights-intro-point-5 = Mae rhai nodweddion { -brand-short-name } yn gwneud defnydd p wasanaethau gwybodaeth gwe, er hynny nid ydym yn gallu gwarantu eu bod yn 100% yn gywir nac yn rhydd o wallau. Mae rhagor o fanylion, gan gynnwys gwybodaeth ar sut i'w hanalluogi i'w cael yn yr <a data-l10n-name="mozilla-service-terms-link">amodau gwasanaeth</a>.
+rights-intro-point-5-unbranded = Os yw'r cynnyrch yn cynnwys gwasanaethau gwe, rhaid cysylltu unrhyw amodau gwasanaeth perthnasol ar gyfer y gwasanaeth(au) i'r adran <a data-l10n-name="mozilla-website-services-link">Gwasanaethau Gwefan</a> Gwe.
+rights-intro-point-6 = Er mwyn chwarae rhai mathau o gynnwys fideo, mae { -brand-short-name } yn llwytho i lawr rhywfaint o gynnwys modiwlau dadgryptio gan drydydd partïon.
+rights-webservices-header = Gwasanaethau Gwybodaeth Gwe { -brand-full-name }
+rights-webservices2 = Mae { -brand-full-name } yn defnyddio gwasanaethau gwybodaeth gwe ("Gwasanaethau") i ddarparu rhai o'r nodweddion sy'n cael eu darparu ar eich cyfer yn y fersiwn yma o { -brand-short-name } o fewn yr amodau disgrifir isod. Os nad ydych am ddefnyddio un neu fwy o'r Gwasanaethau neu mae'r amodau yn annerbyniol, mae modd i chi analluogi'r nodwedd neu'r Gwasanaeth(au). Mae gwybodaeth ar sut i analluogi nodwedd neu Wasanaeth penodol i'w cael <a data-l10n-name="mozilla-disable-service-link">yma</a>. Mae modd analluogi nodweddion a Gwasanaethau eraill yn newisiadau'r rhaglen.
+rights-locationawarebrowsing = <strong>Pori Ymwybodol o Leoliad: </strong>yn ddewis i chi bob tro.  Ni fydd gwybodaeth yn cael ei anfon heb eich caniatâd.  Os hoffech chi analluogi'r nodwedd yn llwyr, dilynwch y camau hyn:
+rights-locationawarebrowsing-term-1 = Yn y bar URL, teipiwch <code>about:config</code>
+rights-locationawarebrowsing-term-2 = Teipio geo.enabled
+rights-locationawarebrowsing-term-3 = Clic dwbl i'r dewis geo.enabled
+rights-locationawarebrowsing-term-4 = Mae Pori Ymwybodol o Leoliad wedi ei analluogi
+rights-webservices-unbranded = Rhaid cynnwys yn fan hyn, drosolwg o'r gwasanaeth gwefan gwe mae'r cynnyrch yn ei gynnwys, ynghyd â chyfarwyddiadau ar sut i'w hatal os yn berthnasol.
+rights-webservices-term-unbranded = Rhaid rhestru amodau gwasanaethau gwe yma.
+rights-webservices-term-1 = Mae { -vendor-short-name } a'i gyfranwyr, trwyddedwyr, a phartneriaid yn gweithio i ddarparu'r Gwasanaethau mwyaf cywir a chyfredol.  Er hynny, nid oes modd i ni warantu fod y wybodaeth yn gynhwysfawr a diwall.  Er enghraifft, efallai na fydd y Gwasanaeth Pori Diogel yn adnabod rhai gwefannau anniogel ac efallai adnabod rhai gwefannau diogel ar gam. Mae pob lleoliad sy'n cael ei ddychwelyd gan ein darparwyr gwasanaeth ar gyfer y Gwasanaeth Ymwybodol o Leoliad yn amcanion yn unig. Nid ydym ni na'r darparwyr gwasanaeth yn gallu gwarantu cywirdeb y lleoliadau hyn.
+rights-webservices-term-2 = Gall { -vendor-short-name } atal neu newid y Gwasanaethau yn ôl eu mympwy.
+rights-webservices-term-3 = Mae croeso i chi ddefnyddio'r Gwasanaethau hyn gyda'r fersiwn yma o { -brand-short-name }, ac mae { -vendor-short-name } rhoi ei hawl i chi wneud hynny.  Mae { -vendor-short-name } a'i drwyddedwyr yn diogelu pob hawl arall yn y Gwasanaethau.  Nid yw'r amodau wedi eu hanelu at gyfyngu unrhyw hawliau o dan drwyddedau cod agored sy'n perthyn i { -brand-short-name } ac i'r fersiynau perthnasol o ffynonellau cod { -brand-short-name }.
+rights-webservices-term-4 = <strong>Mae'r gwasanaeth yn cael ei ddarparu "fel ag y mae".  Mae { -vendor-short-name }, ei gyfranwyr, trwyddedwyr, a dosbarthwyr, yn gwadu unrhyw warant, p'un ai yn cael ei fynegi neu ei awgrymu, gan gynnwys heb gyfyngiad, gwarant fod y Gwasanaethau yn farchnadadwy nac yn addas i'ch pwrpas penodol.  Rydych yn derbyn yr holl risg o ddewis y Gwasanaethau ar gyfer eich pwrpas ac i natur ansawdd a pherfformiad y Gwasanaeth. Nid yw rhai awdurdodau'n caniatáu eithrio neu gyfyngu gwarant sy'n cael ei awgrymu felly efallai nad yw'r gwadiad hwn yn berthnasol i chi.</strong>
+rights-webservices-term-5 = <strong>Yn wahanol i'r hyn sy'n angenrheidiol yn ôl y gyfraith, ni fydd { -vendor-short-name }, ei gyfranwyr, trwyddedwyr a dosbarthwyr yn agored i unrhyw iawndal anuniongyrchol, arbenigol, achlysurol, neu enghreifftiol yn codi o neu mewn unrhyw ffordd yn berthnasol i'r defnydd o { -brand-short-name } a'r Gwasanaethau.   Ni fydd yr atebolrwydd cyfunol o dan yr amodau hyn yn fwy na $500 (pum can dollar). Nid yw rhai awdurdodau yn caniatáu cyfyngu ar rhai materion difrod, felly efallai na fydd hyn yn berthnasol i chi.</strong>
+rights-webservices-term-6 = Gall { -vendor-short-name } ddiweddaru'r amodau yn ôl y galw o bryd i'w gilydd. Nid oes modd newid na dileu'r amodau heb ganiatâd ysgrifenedig { -vendor-short-name }.
+rights-webservices-term-7 = Mae'r amodau yn cael eu rheoli gan gyfreithiau talaith California, UDA, gan hepgor ei ddarpariaethau gwrthdaro cyfreithiol. Os yw unrhyw ran o'r amodau i'w cael heb rym cyfreithiol byd y gweddill yn sefyll mewn grym llawn ac effaith. Os digwydd gwrthdaro rhwng fersiwn sydd wedi ei gyfieithu a'r amodau hyn a'r fersiwn Saesneg, y fersiwn Saesneg fydd yn rheoli.
diff --git a/thunderbird-l10n/cy/localization/cy/messenger/aboutSupportCalendar.ftl b/thunderbird-l10n/cy/localization/cy/messenger/aboutSupportCalendar.ftl
new file mode 100644
index 0000000000..7045b579d4
--- /dev/null
+++ b/thunderbird-l10n/cy/localization/cy/messenger/aboutSupportCalendar.ftl
@@ -0,0 +1,33 @@
+# This Source Code Form is subject to the terms of the Mozilla Public
+# License, v. 2.0. If a copy of the MPL was not distributed with this
+# file, You can obtain one at http://mozilla.org/MPL/2.0/.
+
+calendars-title = Gosodiadau Calendr
+calendars-table-heading-property = Enw
+calendars-table-heading-value = Gwerth
+calendars-table-name = Enw
+calendars-table-type = Math
+calendars-table-disabled = Analluogwyd
+calendars-table-username = Enw Defnyddiwr
+calendars-table-uri = URI
+calendars-table-refreshinterval = Adnewyddu Cyfnod
+calendars-table-readonly = Darllen-yn-unig
+calendars-table-suppressalarms = Atal Larymau
+calendars-table-cache-enabled = Cache Wedi'i Alluogi
+calendars-table-imip-identity = Hunaniaeth iMIP
+calendars-table-imip-identity-disabled = iMIP Wedi'i Analluogi
+calendars-table-imip-identity-account = Cyfrif iMIP
+calendars-table-organizerid = Enw'r Trefnydd
+calendars-table-forceemailscheduling = Gorfodi Amserlennu E-bost
+calendars-table-capabilities-alarms-popup-supported = Larymau Llamu sy'n cael eu Cefnogi
+calendars-table-capabilities-alarms-oninviations-supported = Larymau Gwahoddiad sy'n cael eu Cefnogi
+calendars-table-capabilities-alarms-maxcount = Uchafswm y Larymau Fesul Digwyddiad
+calendars-table-capabilities-attachments-supported = Atodiadau sy'n cael eu Cefnogi
+calendars-table-capabilities-categories-maxcount = Uchafswm y Categorïau
+calendars-table-capabilities-privacy-supported = Cyflyrau Preifatrwydd sy'n cael eu Cefnogi
+calendars-table-capabilities-priority-supported = Blaenoriaethau sy'n cael eu Cefnogi
+calendars-table-capabilities-events-supported = Digwyddiadau sy'n cael eu Cefnogi
+calendars-table-capabilities-tasks-supported = Tasgau sy'n cael eu Cefnogi
+calendars-table-capabilities-timezones-floating-supported = Amserau Lleol sy'n cael eu Cefnogi
+calendars-table-capabilities-timezones-utc-supported = UTC/GMT yn cael eu Cefnogi
+calendars-table-capabilities-autoschedule-supported = Auto-Amserlennu yn cael ei Gefnogi
diff --git a/thunderbird-l10n/cy/localization/cy/messenger/aboutSupportChat.ftl b/thunderbird-l10n/cy/localization/cy/messenger/aboutSupportChat.ftl
new file mode 100644
index 0000000000..df11065de7
--- /dev/null
+++ b/thunderbird-l10n/cy/localization/cy/messenger/aboutSupportChat.ftl
@@ -0,0 +1,11 @@
+# This Source Code Form is subject to the terms of the Mozilla Public
+# License, v. 2.0. If a copy of the MPL was not distributed with this
+# file, You can obtain one at http://mozilla.org/MPL/2.0/.
+
+chat-title = Cyfrifon Sgwrsio
+chat-table-heading-account = ID
+chat-table-heading-protocol = Protocol
+chat-table-heading-name = Enw
+chat-table-heading-actions = Gweithredoedd
+chat-table-copy-debug-log = Copïo'r Cofnod Dadfygio
+    .title = Copïo gwallau a chofnodio eraill o'r cyfrif sgwrsio hwn i'r clipfwrdd. Gall gynnwys manylion personol fel negeseuon sgwrsio.
diff --git a/thunderbird-l10n/cy/localization/cy/messenger/aboutSupportMail.ftl b/thunderbird-l10n/cy/localization/cy/messenger/aboutSupportMail.ftl
new file mode 100644
index 0000000000..660298d82c
--- /dev/null
+++ b/thunderbird-l10n/cy/localization/cy/messenger/aboutSupportMail.ftl
@@ -0,0 +1,31 @@
+# This Source Code Form is subject to the terms of the Mozilla Public
+# License, v. 2.0. If a copy of the MPL was not distributed with this
+# file, You can obtain one at http://mozilla.org/MPL/2.0/.
+
+accounts-title = Cyfrifon E-bost a Newyddion
+show-private-data-main-text = Cynnwys enwau cyfrifon
+show-private-data-explanation-text = (manylion adnabod personol posib)
+accounts-ID = ID
+accounts-name = Enw
+accounts-incoming-server = Gweinydd Derbyn
+accounts-outgoing-servers = Gweinydd Allan
+accounts-server-name = Enw
+accounts-conn-security = Diogelwch cysylltiad
+accounts-auth-method = Dull dilysu
+accounts-default = Rhagosodiad?
+identity-name = hunaniaeth
+send-via-email = Anfon drwy e-bost
+app-basics-telemetry = Data Telemetreg
+app-basics-cache-use = Defnydd Storfan
+mail-libs-title = Llyfrgelloedd
+libs-table-heading-library = Llyfrgell
+libs-table-heading-expected-version = Fersiwn lleiaf disgwyliedig
+libs-table-heading-loaded-version = Fersiwn yn cael ei ddefnyddio
+libs-table-heading-path = Llwybr
+libs-table-heading-status = Statws
+libs-rnp-status-ok = Iawn
+libs-rnp-status-load-failed = Wedi methu llwytho. Ni fydd OpenPGP yn gweithio.
+libs-rnp-status-incompatible = Fersiwn anghydnaws. Ni fydd OpenPGP yn gweithio.
+libs-rnp-status-unofficial = Fersiwn answyddogol. Efallai na fydd OpenPGP yn gweithio yn ôl y disgwyl.
+libs-otr-status-ok = Iawn
+libs-otr-status-error = Wedi methu llwytho. Ni fydd amgryptio sgwrs OTR yn gweithio.
diff --git a/thunderbird-l10n/cy/localization/cy/messenger/accountCentral.ftl b/thunderbird-l10n/cy/localization/cy/messenger/accountCentral.ftl
new file mode 100644
index 0000000000..4eb5fc48de
--- /dev/null
+++ b/thunderbird-l10n/cy/localization/cy/messenger/accountCentral.ftl
@@ -0,0 +1,50 @@
+# This Source Code Form is subject to the terms of the Mozilla Public
+# License, v. 2.0. If a copy of the MPL was not distributed with this
+# file, You can obtain one at http://mozilla.org/MPL/2.0/.
+
+account-central-title = Croeso i { -brand-full-name }
+account-settings = Gosodiadau Cyfrif
+#   $accounts (Number) - the number of configured accounts
+setup-title = Dewis Beth i'w Osod
+about-title = Ynghylch { -brand-full-name }
+resources-title = Adnoddau
+release-notes =
+    .title = Ynghylch { -brand-full-name }
+email-label = E-bost
+    .aria-label = Cysylltu i'ch cyfeiriad e-bost cyfredol
+email-description = Mae { -brand-short-name } yn galluogi chi gysylltu â'ch cyfrif e-bost presennol, i ddarllen eich e-byst yn gyfleus ac yn effeithlon o fewn y rhaglen.
+calendar-label = Calendr
+    .aria-label = Creu calendr newydd
+calendar-description = Mae { -brand-short-name } yn galluogi i chi drin digwyddiadau a chadw trefn. Bydd cysylltu â chalendr pell yn cydweddu'ch holl ddigwyddiadau ar draws eich holl ddyfeisiau.
+chat-label = Sgwrsio
+    .aria-label = Cysylltu â'ch cyfrif sgwrsio
+chat-description = Mae { -brand-short-name } yn galluogi i chi gysylltu â sawl cyfrif negeseua chwim, gan gynnig cefnogaeth i nifer o lwyfannau amrywiol.
+filelink-label = Filelink
+    .aria-label = Gosod Filelink
+filelink-description = Mae { -brand-short-name } yn galluogi i chi greu cyfrif Filelink cwmwl cyfleus i anfon atodiadau mawr yn hawdd.
+addressbook-label = Llyfr Cyfeiriadau
+    .aria-label = Creu llyfr cyfeiriadau newydd
+addressbook-description = Mae { -brand-short-name } yn galluogi i chi drefnu'ch holl gysylltiadau mewn llyfr cyfeiriadau. Gallwch hefyd gysylltu â llyfr cyfeiriadau o bell i gydweddu'ch holl gysylltiadau.
+feeds-label = Llif
+    .aria-label = Cysylltu â llifau
+feeds-description = Mae { -brand-short-name } yn galluogi i chi gysylltu â phorthwyr RSS / Atom i gael newyddion a diweddariadau o bob man.
+newsgroups-label = Grwpiau Newyddion
+    .aria-label = Cysylltu â grŵp newyddion
+newsgroups-description = Mae { -brand-short-name } yn galluogi i chi gysylltu â'r holl grwpiau newyddion yr hoffech chi
+import-title = Mewnforio o Raglen Arall
+import-paragraph2 = Mae { -brand-short-name } yn galluogi i chi fewnforio negeseuon e-bost, cofnodion llyfr cyfeiriadau, tanysgrifiadau llif, dewisiadau, a/neu hidlwyr o raglenni e-bost eraill a fformatau llyfrau cyfeiriadau cyffredin.
+import-label = Mewnforio
+    .aria-label = Mewnforio data o raglenni eraill
+about-paragraph = Thunderbird yw'r brif raglen e-bost a chalendr, croes blatfform, cod agored, sydd ar gael am ddim ar gyfer defnydd busnes neu bersonol. Rydym am barhau i'w gadw'n ddiogel ac i'w wella i'r dyfodol. Bydd rhoddion yn caniatáu i ni gyflogi datblygwyr, talu am isadeiledd a pharhau i'w wella.
+about-paragraph-consider-donation = <b>Mae Thunderbird yn cael ei ariannu gan ddefnyddwyr fel chi! Os ydych chi'n hoffi Thunderbird, ystyriwch wneud rhodd.</b> Y ffordd orau i wneud yn siŵr fod Thunderbird yn parhau i fod ar gael yw <a data-l10n-name="donation-link"> i wneud cyfraniad.</a>
+explore-link = Edrych ar y Nodweddion
+support-link = Cefnogaeth
+involved-link = Ymunwch
+developer-link = Dogfennaeth Datblygwr
+read = Darllen negeseuon
+compose = Ysgrifennu neges newydd
+search = Chwilio drwy'r Negeseuon
+filter = Rheoli hidlau negeseuon
+nntp-subscription = Rheoli tanysgrifiadau grwpiau newyddion
+rss-subscription = Rheoli tanysgrifiadau llif
+e2e = Amgryptio Pen-i-Ben
diff --git a/thunderbird-l10n/cy/localization/cy/messenger/accountManager.ftl b/thunderbird-l10n/cy/localization/cy/messenger/accountManager.ftl
new file mode 100644
index 0000000000..1a489603ed
--- /dev/null
+++ b/thunderbird-l10n/cy/localization/cy/messenger/accountManager.ftl
@@ -0,0 +1,18 @@
+# This Source Code Form is subject to the terms of the Mozilla Public
+# License, v. 2.0. If a copy of the MPL was not distributed with this
+# file, You can obtain one at http://mozilla.org/MPL/2.0/.
+
+open-preferences-sidebar-button2 = Gosodiadau { -brand-short-name }
+
+open-addons-sidebar-button = Ychwanegion a Themâu
+
+account-action-add-newsgroup-account =
+    .label = Ychwanegu Cyfrif Grŵp Newyddion…
+    .accesskey = G
+
+server-change-restart-required = Mae angen ailgychwyn i osod enw'r gweinydd neu'r newid enw defnyddiwr.
+
+edit-vcard-dialog-accept-button = Cadw
+    .accesskey = C
+edit-vcard-dialog-cancel-button = Diddymu
+    .accesskey = D
diff --git a/thunderbird-l10n/cy/localization/cy/messenger/accountProvisioner.ftl b/thunderbird-l10n/cy/localization/cy/messenger/accountProvisioner.ftl
new file mode 100644
index 0000000000..f579c2e60f
--- /dev/null
+++ b/thunderbird-l10n/cy/localization/cy/messenger/accountProvisioner.ftl
@@ -0,0 +1,61 @@
+# This Source Code Form is subject to the terms of the Mozilla Public
+# License, v. 2.0. If a copy of the MPL was not distributed with this
+# file, You can obtain one at http://mozilla.org/MPL/2.0/.
+
+account-provisioner-tab-title = Cael cyfeiriad e-bost newydd gan ddarparwr gwasanaeth
+provisioner-searching-icon =
+    .alt = Yn chwilio…
+account-provisioner-title = Creu cyfeiriad e-bost newydd
+account-provisioner-description = Defnyddiwch ein partneriaid dibynadwy i gael cyfeiriad e-bost preifat a diogel newydd.
+account-provisioner-start-help = Mae'r termau chwilio sydd wedi'u defnyddio'n cael eu anfon at { -vendor-short-name } (<a data-l10n-name="mozilla-privacy-link">Polisi Preifatrwydd</a>) a darparwyr e-bost 3ydd parti <strong>mailfence.com</strong> (<a data-l10n-name="mailfence-privacy-link">Polisi Preifatrwydd</a>, <a data-l10n-name="mailfence-tou-link">Telerau Defnyddio</ a >) a <strong>gandi.net</strong> (<a data-l10n-name="gandi-privacy-link">Polisi Preifatrwydd</a>, <a data-l10n-name="gandi-tou-link">Amodau Defnydd</a>) i ganfod cyfeiriadau e-bost sydd ar gael.
+account-provisioner-mail-account-title = Prynu cyfeiriad e-bost newydd
+account-provisioner-mail-account-description = Mae Thunderbird wedi partneru â <a data-l10n-name="mailfence-home-link">Mailfence</a> i gynnig e-bost preifat a diogel newydd i chi. Credwn y dylai pawb gael e-bost diogel.
+account-provisioner-domain-title = Prynwch e-bost a pharth i chi eich hun
+account-provisioner-domain-description = Mae Thunderbird wedi partneru â <a data-l10n-name="gandi-home-link">Gandi</a> i gynnig parth cyfaddas i chi. Mae hyn yn caniatáu i chi ddefnyddio unrhyw gyfeiriad ar y parth hwnnw.
+
+## Forms
+
+account-provisioner-mail-input =
+    .placeholder = Eich enw, llysenw neu derm chwilio arall
+account-provisioner-domain-input =
+    .placeholder = Eich enw, llysenw neu derm chwilio arall
+account-provisioner-search-button = Chwilio
+account-provisioner-button-cancel = Diddymu
+account-provisioner-button-existing = Defnyddiwch gyfrif e-bost sy'n bodoli eisoes
+account-provisioner-button-back = Mynd nôl
+
+## Notifications
+
+account-provisioner-fetching-provisioners = Yn estyn darprwyr…
+account-provisioner-connection-issues = Nid ydym yn gallu cyfathrebu gyda'n gweinydd cofrestru. Gwiriwch eich cysylltiad.
+account-provisioner-searching-email = Yn chwilio am gyfrifon e-bost sydd ar gael...
+account-provisioner-searching-domain = Yn chwilio am y parthau sydd ar gael...
+account-provisioner-searching-error = Methu dod o hyd i unrhyw gyfeiriadau i'w cynnig. Ceisiwch newid y termau chwilio.
+
+## Illustrations
+
+account-provisioner-step1-image =
+    .title = Dewiswch pa gyfrif i'w greu
+
+## Search results
+
+# Variables:
+# $count (Number) - The number of domains found during search.
+account-provisioner-results-title =
+    { $count ->
+        [zero] Dim cyfeiriadau ar gael ar gyfer:
+        [one] Un cyfeiriad ar gael ar gyfer:
+        [two] { $count } gyfeiriad ar gael ar gyfer:
+        [few] { $count } cyfeiriad ar gael ar gyfer:
+        [many] { $count } chyfeiriad ar gael ar gyfer:
+       *[other] { $count } cyfeiriad ar gael ar gyfer:
+    }
+account-provisioner-mail-results-caption = Gallwch hefyd chwilio am lysenwau neu dermau eraill i ganfod ragor o e-byst eraill.
+account-provisioner-domain-results-caption = Gallwch hefyd chwilio am lysenwau neu dermau eraill i ganfod ragor o barthau  eraill.
+account-provisioner-free-account = Rhydd
+# Variables:
+# $price (String) - Yearly fee for the mail account. For example "US $9.99".
+account-provision-price-per-year = { $price } y flwyddyn
+account-provisioner-all-results-button = Dangos yr holl ganlyniadau
+account-provisioner-open-in-tab-img =
+    .title = Yn agor mewn Tab newydd
diff --git a/thunderbird-l10n/cy/localization/cy/messenger/accountcreation/accountHub.ftl b/thunderbird-l10n/cy/localization/cy/messenger/accountcreation/accountHub.ftl
new file mode 100644
index 0000000000..e13d8027a7
--- /dev/null
+++ b/thunderbird-l10n/cy/localization/cy/messenger/accountcreation/accountHub.ftl
@@ -0,0 +1,83 @@
+# This Source Code Form is subject to the terms of the Mozilla Public
+# License, v. 2.0. If a copy of the MPL was not distributed with this
+# file, You can obtain one at http://mozilla.org/MPL/2.0/.
+
+
+### Account Hub
+### Account hub is where user can setup new accounts in Thunderbird.
+
+
+## Header
+
+account-hub-brand = { -brand-full-name }
+account-hub-welcome-line = Croeso i <span data-l10n-name="brand-name">{ -brand-full-name }</span>
+account-hub-title = Canolfan Cyfrifon
+
+## Footer
+
+account-hub-release-notes = Nodiadau ryddhau
+account-hub-support = Cefnogaeth
+account-hub-donate = Cyfrannu
+
+## Initial setup page
+
+account-hub-email-setup-button = Cyfrif E-bost
+    .title = Creu cyfrif e-bost
+account-hub-calendar-setup-button = Calendr
+    .title = Creu calendr lleol neu bell
+account-hub-address-book-setup-button = Llyfr Cyfeiriadau
+    .title = Creu llyfr cyfeiriadau lleol neu bell
+account-hub-chat-setup-button = Sgwrsio
+    .title = Creu cyfrif sgwrsio
+account-hub-feed-setup-button = Llif RSS
+    .title = Creu cyfrif llif RSS
+account-hub-newsgroup-setup-button = Grŵp Newyddion
+    .title = Creu cyfrif grŵp newyddion
+account-hub-import-setup-button = Mewnforio
+    .title = Mewnforio proffil wrth gefn
+# Note: "Sync" represents the Firefox Sync product so it shouldn't be translated.
+account-hub-sync-button = Mewngofnodi i Sync…
+
+## Email page
+
+account-hub-email-title = Creu cyfrif e-bost
+account-hub-add-email-title = Ychwanegu Eich Cyfrif
+account-hub-manually-configure-email-title = Gosod Ffurfweddu Cyfrif
+account-hub-email-cancel-button = Diddymu
+account-hub-email-stop-button = Atal
+account-hub-email-back-button = Nôl
+account-hub-email-retest-button = Ailbrofi
+account-hub-email-finish-button = Gorffen
+account-hub-email-manually-configure-button = Ffurfweddu â Llaw
+account-hub-email-continue-button = Parhau
+account-hub-email-confirm-button = Cadarnhau
+account-hub-incoming-server-legend = Gweinydd derbyn
+account-hub-outgoing-server-legend = Gweinydd anfon
+account-hub-protocol-label = Protocol
+account-hub-hostname-label = Enw Gwesteiwr
+account-hub-port-label = Porth
+    .title = Gosodwch rif y porthladd i 0 ar gyfer canfod awtomatig
+account-hub-auto-description = Bydd { -brand-short-name } yn ceisio awtoganfod meysydd sy'n cael eu gadael yn wag.
+account-hub-ssl-label = Diogelwch cysylltiad
+
+## Incoming/Outgoing SSL Authentication options
+
+account-hub-ssl-autodetect-option =
+    .label = Awtoganfod
+account-hub-ssl-no-authentication-option =
+    .label = Dim dilysiad
+account-hub-ssl-cleartext-password-option =
+    .label = Cyfrinair arferol
+account-hub-ssl-encrypted-password-option =
+    .label = Cyfrinair wedi'i amgryptio
+
+## Incoming/Outgoing SSL options
+
+account-hub-ssl-noencryption-option =
+    .label = Dim
+account-hub-auth-label = Dull dilysu
+account-hub-username-label = Enw Defnyddiwr
+account-hub-adding-account-title = Ychwanegu Cyfrif
+account-hub-adding-account-subheader = Ail-brofi gosodiadau ffurfweddiad cyfrif
+account-hub-account-added-title = Ychwanegwyd Cyfrif
+account-hub-find-settings-failed = Methodd { -brand-full-name } â dod o hyd i'r gosodiadau ar gyfer eich cyfrif e-bost.
diff --git a/thunderbird-l10n/cy/localization/cy/messenger/accountcreation/accountSetup.ftl b/thunderbird-l10n/cy/localization/cy/messenger/accountcreation/accountSetup.ftl
new file mode 100644
index 0000000000..a18ee392b3
--- /dev/null
+++ b/thunderbird-l10n/cy/localization/cy/messenger/accountcreation/accountSetup.ftl
@@ -0,0 +1,310 @@
+# This Source Code Form is subject to the terms of the Mozilla Public
+# License, v. 2.0. If a copy of the MPL was not distributed with this
+# file, You can obtain one at http://mozilla.org/MPL/2.0/.
+
+account-setup-tab-title = Gosod Cyfrif
+
+## Header
+
+account-setup-title = Gosod eich Cyfrif E-bost Cyfredol
+account-setup-description =
+    I ddefnyddio'ch cyfeiriad e-bost cyfredol, llenwch eich manylion. <br/>
+    Bydd { -brand-product-name } yn chwilio'n awtomatig am ffurfweddid gweinydd sy'n gweithio ac sy'n cael ei argymell.
+account-setup-secondary-description = Bydd { -brand-product-name } yn chwilio'n awtomatig am ffurfweddiad gweinydd sy'n gweithio ac sy'n cael ei argymell.
+account-setup-success-title = Cyfrif wedi'i greu'n llwyddiannus
+account-setup-success-description = Nawr gallwch chi ddefnyddio'r cyfrif hwn gyda { -brand-short-name }.
+account-setup-success-secondary-description = Gallwch wella'r profiad trwy gysylltu gwasanaethau cysylltiedig a ffurfweddu gosodiadau cyfrifon uwch.
+
+## Form fields
+
+account-setup-name-label = Eich enw llawn
+    .accesskey = e
+# Note: "John Doe" is a multiple-use name that is used when the true name of a person is unknown. We use this fake name as an input placeholder. Translators should update this to reflect the placeholder name of their language/country.
+account-setup-name-input =
+    .placeholder = John Jones
+account-setup-name-info-icon =
+    .title = Eich enw, fel mae'n cael ei ddangos i eraill
+account-setup-name-warning-icon =
+    .title = Rhowch eich enw
+account-setup-email-label = Cyfeiriad e-bost
+    .accesskey = C
+account-setup-email-input =
+    .placeholder = john.jones@example.com
+account-setup-email-info-icon =
+    .title = Eich cyfeiriad e-bost cyfredol
+account-setup-email-warning-icon =
+    .title = Cyfeiriad e-bost annilys
+account-setup-password-label = Cyfrinair
+    .accesskey = y
+    .title = Yn ddewisol, dim ond i'w ddefnyddio i ddilysu'r enw defnyddiwr
+account-provisioner-button = Cael cyfeiriad e-bost newydd
+    .accesskey = n
+account-setup-password-toggle-show =
+    .title = Dangos cyfrinair mewn testun clir
+account-setup-password-toggle-hide =
+    .title = Cuddio cyfrinair
+account-setup-remember-password = Cofio'r cyfrinair
+    .accesskey = o
+account-setup-exchange-label = Eich mewngofnod
+    .accesskey = m
+#   YOURDOMAIN refers to the Windows domain in ActiveDirectory. yourusername refers to the user's account name in Windows.
+account-setup-exchange-input =
+    .placeholder = YOURDOMAIN\yourusername
+#   Domain refers to the Windows domain in ActiveDirectory. We mean the user's login in Windows at the local corporate network.
+account-setup-exchange-info-icon =
+    .title = Mewngofnod parth
+
+## Action buttons
+
+account-setup-button-cancel = Diddymu
+    .accesskey = D
+account-setup-button-manual-config = Ffurfweddu â llaw
+    .accesskey = F
+account-setup-button-stop = Atal
+    .accesskey = A
+account-setup-button-retest = Ailbrofi
+    .accesskey = A
+account-setup-button-continue = Parhau
+    .accesskey = P
+account-setup-button-done = Wedi gorffen
+    .accesskey = W
+
+## Notifications
+
+account-setup-looking-up-settings = Chwilio am y ffurfweddiad…
+account-setup-looking-up-settings-guess = Yn chwilio drwy'r ffurfweddiad: Yn rhoi cynnig ar enwau gweinydd cyffredin ...
+account-setup-looking-up-settings-half-manual = Yn chwilio drwy'r ffurfweddiad: Yn holi'r gweinydd...
+account-setup-looking-up-disk = Yn chwilio drwy'r ffurfweddiad: yn gosod { -brand-short-name }…
+account-setup-looking-up-isp = Yn chwilio drwy'r ffurfweddiad: Darparwyr e-bost…
+# Note: Do not translate or replace Mozilla. It stands for the public project mozilla.org, not Mozilla Corporation. The database is a generic, public domain facility usable by any client.
+account-setup-looking-up-db = Yn chwilio drwy'r ffurfweddiad: cronfa ddata ISP Mozilla...
+account-setup-looking-up-mx = Yn chwilio drwy'r ffurfweddiad: Parthau derbyn e-bost...
+account-setup-looking-up-exchange = Yn chwilio drwy'r ffurfweddiad: Gweinydd Exchange...
+account-setup-checking-password = Yn gwirio'r cyfrinair...
+account-setup-installing-addon = Wrthi'n llwytho i lawr a gosod ychwanegyn…
+account-setup-success-half-manual = Canfuwyd y gosodiadau canlynol trwy archwilio'r gweinydd hwn:
+account-setup-success-guess = Canfuwyd y ffurfweddiad drwy roi cynnig ar enwau gweinydd cyffredin.
+account-setup-success-guess-offline = Rydych all-lein. Rydym wedi dyfalu rhai gosodiadau ond bydd angen i chi osod y gosodiadau cywir.
+account-setup-success-password = Cyfrinair yn iawn
+account-setup-success-addon = Wedi gosod yr ychwanegyn yn llwyddiannus
+# Note: Do not translate or replace Mozilla. It stands for the public project mozilla.org, not Mozilla Corporation. The database is a generic, public domain facility usable by any client.
+account-setup-success-settings-db = Ffurfweddiad wedi'i ganfod yng nghronfa ddata ISP Mozilla.
+account-setup-success-settings-disk = Ffurfweddiad wedi'i ganfod ar osodiad { -brand-short-name }.
+account-setup-success-settings-isp = Ffurfweddiad wedi'i ganfod yn y darparwr e-bost.
+# Note: Microsoft Exchange is a product name.
+account-setup-success-settings-exchange = Ffurfweddiad wedi'i ganfod ar gyfer gweinydd Microsoft Exchange.
+
+## Illustrations
+
+account-setup-step1-image =
+    .title = Gosodiad cychwynnol
+account-setup-step2-image =
+    .title = Yn llwytho…
+account-setup-step3-image =
+    .title = Wedi canfod ffurfweddiad
+account-setup-step4-image =
+    .title = Gwall cysylltiad
+account-setup-step5-image =
+    .title = Cyfrif wedi'i greu
+account-setup-privacy-footnote2 = Dim ond ar eich cyfrifiadur y bydd eich manylion yn cael eu storio'n lleol.
+account-setup-selection-help = Ddim yn siŵr beth i'w ddewis?
+account-setup-selection-error = Angen cymorth?
+account-setup-success-help = Ddim yn siŵr am eich camau nesaf?
+account-setup-documentation-help = Dogfennaeth gosod
+account-setup-forum-help = Fforwm cefnogi
+account-setup-privacy-help = Polisi preifatrwydd
+account-setup-getting-started = Cychwyn arni
+
+## Results area
+
+# Variables:
+#  $count (Number) - Number of available protocols.
+account-setup-results-area-title =
+    { $count ->
+        [zero] Ffurfwediadau ar gael
+        [one] Ffurfwediadau ar gael
+        [two] Ffurfwediadau ar gael
+        [few] Ffurfwediadau ar gael
+        [many] Ffurfwediadau ar gael
+       *[other] Ffurfwediadau ar gael
+    }
+account-setup-result-imap-description = Cadw eich ffolderi a'ch e-byst wedi'u cydweddu ar eich gweinydd
+account-setup-result-pop-description = Cadw eich ffolderi a'ch e-byst ar eich cyfrifiadur
+# Note: Exchange, Office365 are the name of products.
+account-setup-result-exchange2-description = Defnyddiwch weinydd Microsoft Exchange neu wasanaethau cwmwl Office365
+account-setup-incoming-title = Derbyn
+account-setup-outgoing-title = Anfon
+account-setup-username-title = Enw Defnyddiwr
+account-setup-exchange-title = Gweinydd
+account-setup-result-no-encryption = Dim Amgryptiad
+account-setup-result-ssl = SSL/TLS
+account-setup-result-starttls = STARTTLS
+account-setup-result-outgoing-existing = Defnyddio'r gweinydd SMTP anfon cyfredol
+# Variables:
+#  $incoming (String): The email/username used to log into the incoming server
+#  $outgoing (String): The email/username used to log into the outgoing server
+account-setup-result-username-different = Derbyn: { $incoming }, Anfon: { $outgoing }
+
+## Error messages
+
+# Note: The reference to "janedoe" (Jane Doe) is the name of an example person. You will want to translate it to whatever example persons would be named in your language. In the example, AD is the name of the Windows domain, and this should usually not be translated.
+account-setup-credentials-incomplete = Methodd y dilysu. Naill ai mae'r manylion a gofnodwyd yn anghywir neu mae angen enw defnyddiwr ar wahân ar gyfer mewngofnodi. Yr enw defnyddiwr hwn fel rheol yw eich mewngofnod parth Windows gyda'r parth neu hebddo (er enghraifft, sianjones neu AD\\sianjones)
+account-setup-credentials-wrong = Methodd y dilysu. Gwiriwch yr enw defnyddiwr a'r cyfrinair
+account-setup-find-settings-failed = Methodd { -brand-short-name } â dod o hyd i'r gosodiadau ar gyfer eich cyfrif e-bost
+account-setup-exchange-config-unverifiable = Nid oedd modd dilysu eich ffurfweddiad. Os yw'ch enw defnyddiwr a'ch cyfrinair yn gywir, mae'n debygol bod gweinyddwr y gweinydd wedi analluogi'r ffurfweddiad a ddewiswyd ar gyfer eich cyfrif. Ceisiwch ddewis protocol arall.
+account-setup-provisioner-error = Digwyddodd gwall wrth osod eich cyfrif newydd yn { -brand-short-name }. Ceisiwch osod eich cyfrif gyda'ch manylion, â llaw.
+
+## Manual configuration area
+
+account-setup-manual-config-title = Gosodiadau gweinydd
+account-setup-incoming-server-legend = Gweinydd Derbyn
+account-setup-protocol-label = Protocol:
+account-setup-hostname-label = Enw Gwesteiwr:
+account-setup-port-label = Porth:
+    .title = Gosod rhif y porth i 0 ar gyfer awtoganfod
+account-setup-auto-description = Bydd { -brand-short-name } yn ceisio awtoganfod meysydd sy'n cael eu gadael yn wag.
+account-setup-ssl-label = Diogelwch y cysylltiad:
+account-setup-outgoing-server-legend = Gweinydd anfon
+
+## Incoming/Outgoing SSL Authentication options
+
+ssl-autodetect-option = Awtoganfod
+ssl-no-authentication-option = Dim dilysiad
+ssl-cleartext-password-option = Cyfrinair arferol
+ssl-encrypted-password-option = Cyfrinair wedi'i amgryptio
+
+## Incoming/Outgoing SSL options
+
+ssl-noencryption-option = Dim
+account-setup-auth-label = Dull dilysu:
+account-setup-username-label = Enw Defnyddiwr:
+account-setup-advanced-setup-button = Ffurfweddiad uwch
+    .accesskey = F
+
+## Warning insecure server dialog
+
+account-setup-insecure-title = Rhybudd!
+account-setup-insecure-incoming-title = Gosodiadau derbyn:
+account-setup-insecure-outgoing-title = Gosodiadau anfon:
+# Variables:
+#  $server (String): The name of the hostname of the server the user was trying to connect to.
+account-setup-warning-cleartext = Nid yw <b>{ $server }</b> yn defnyddio amgryptio.
+account-setup-warning-cleartext-details = Nid yw gweinyddion e-bost anniogel yn defnyddio cysylltiadau wedi'u hamgryptio i ddiogelu eich cyfrinair a manylion preifat. Drwy gysylltu â'r gweinydd yma mae modd i chi amlygu eich cyfrinair a manylion preifat.
+account-setup-insecure-server-checkbox = Rwy'n deall y peryglon
+    .accesskey = p
+account-setup-insecure-description = Mae { -brand-short-name } yn gallu caniatáu i chi estyn eich e-bost drwy ddefnyddio'r ffurfweddiad parod. Er hynny, dylech gysylltu â'ch gweinyddwr neu ddarparwr e-bost ynghylch cysylltiadau anaddas. Gw. <a data-l10n-name="thunderbird-faq-link">Cwestiynau Thunderbird</a> am ragor o wybodaeth.
+insecure-dialog-cancel-button = Newid Gosodiadau
+    .accesskey = G
+insecure-dialog-confirm-button = Cadarnhau
+    .accesskey = C
+
+## Warning Exchange confirmation dialog
+
+# Variables:
+#  $domain (String): The name of the server where the configuration was found, e.g. rackspace.com.
+exchange-dialog-question = Mae { -brand-short-name } wedi canfod manylion gosod eich cyfrif ar { $domain }. Hoffech chi barhau a chyflwyno'ch manylion?
+exchange-dialog-confirm-button = Mewngofnodi
+exchange-dialog-cancel-button = Diddymu
+
+## Dismiss account creation dialog
+
+exit-dialog-title = Nid oes Cyfrif E-bost wedi'i Ffurfweddu
+exit-dialog-description = Ydych chi'n siŵr eich bod chi am ddiddymu'r broses osod? Mae modd dal i ddefnyddio { -brand-short-name } heb gyfrif e-bost, ond fydd yna ddim llawer o nodweddion ar gael.
+account-setup-no-account-checkbox = Defnyddio { -brand-short-name } heb gyfrif e-bost
+    .accesskey = D
+exit-dialog-cancel-button = Parhau i Osod
+    .accesskey = P
+exit-dialog-confirm-button = Gadael Gosod
+    .accesskey = G
+
+## Alert dialogs
+
+account-setup-creation-error-title = Gwall wrth Greu Cyfrif
+account-setup-error-server-exists = Mae'r gweinydd derbyn yn bodoli eisoes.
+account-setup-confirm-advanced-title = Cadarnhau Ffurfweddiad Uwch
+account-setup-confirm-advanced-description = Bydd y ddeialog hon yn cael ei chau a bydd cyfrif gyda'r gosodiadau cyfredol yn cael ei greu, hyd yn oed os yw'r ffurfweddiad yn anghywir. Hoffech chi barhau?
+
+## Addon installation section
+
+account-setup-addon-install-title = Gosod
+account-setup-addon-install-intro = Gall ychwanegyn trydydd parti ganiatáu i chi gael mynediad at eich cyfrif e-bost ar y gweinydd hwn:
+account-setup-addon-no-protocol = Yn anffodus nid yw'r gweinydd e-bost hwn yn cefnogi protocolau agored. { account-setup-addon-install-intro }
+
+## Success view
+
+account-setup-settings-button = Gosodiadau cyfrif
+account-setup-encryption-button = Amgryptio pen-i-ben
+account-setup-signature-button = Ychwanegwch lofnod
+account-setup-dictionaries-button = Llwytho geiriadur i lawr
+account-setup-address-book-carddav-button = Cysylltu â llyfr cyfeiriadau CardDAV
+account-setup-address-book-ldap-button = Cysylltu â llyfr cyfeiriadau LDAP
+account-setup-calendar-button = Cysylltu â chalendr pell
+account-setup-linked-services-title = Cysylltwch eich gwasanaethau cysylltiedig
+account-setup-linked-services-description = Mae { -brand-short-name } wedi canfod gwasanaethau eraill sy'n gysylltiedig â'ch cyfrif e-bost.
+account-setup-no-linked-description = Gosod gwasanaethau eraill i gael y gorau o'ch profiad gyda { -brand-short-name }.
+# Variables:
+# $count (Number) - The number of address books found during autoconfig.
+account-setup-found-address-books-description =
+    { $count ->
+        [zero] Nid yw { -brand-short-name } wedi canfod unrhyw wasanaeth arall sy'n gysylltiedig â'ch cyfrif e-bost.
+        [one] Mae { -brand-short-name } wedi canfod { $count } gwasanaeth arall sy'n gysylltiedig â'ch cyfrif e-bost.
+        [two] Mae { -brand-short-name } wedi canfod  { $count } wasanaeth arall sy'n gysylltiedig â'ch cyfrif e-bost.
+        [few] Mae { -brand-short-name } wedi canfod  { $count } gwasanaeth arall sy'n gysylltiedig â'ch cyfrif e-bost.
+        [many] Mae { -brand-short-name } wedi canfod  { $count } gwasanaeth arall sy'n gysylltiedig â'ch cyfrif e-bost.
+       *[other] Mae { -brand-short-name } wedi canfod  { $count } gwasanaeth arall sy'n gysylltiedig â'ch cyfrif e-bost.
+    }
+# Variables:
+# $count (Number) - The number of calendars found during autoconfig.
+account-setup-found-calendars-description =
+    { $count ->
+        [zero] Nid yw { -brand-short-name } wedi canfod  unrhyw galendr arall sy'n gysylltiedig â'ch cyfrif e-bost.
+        [one] Mae { -brand-short-name } wedi canfod  { $count } calendr arall sy'n gysylltiedig â'ch cyfrif e-bost.
+        [two] Mae { -brand-short-name } wedi canfod  { $count } galendr arall sy'n gysylltiedig â'ch cyfrif e-bost.
+        [few] Mae { -brand-short-name } wedi canfod  { $count } chalendr arall sy'n gysylltiedig â'ch cyfrif e-bost.
+        [many] Mae { -brand-short-name } wedi canfod  { $count } chalendr arall sy'n gysylltiedig â'ch cyfrif e-bost.
+       *[other] Mae { -brand-short-name } wedi canfod  { $count } calendr arall sy'n gysylltiedig â'ch cyfrif e-bost.
+    }
+account-setup-button-finish = Gorffen
+    .accesskey = G
+account-setup-looking-up-address-books = Chwilio drwy lyfrau cyfeiriadau…
+account-setup-looking-up-calendars = Chwilio drwy galendrau…
+account-setup-address-books-button = Llyfrau Cyfeiriadau
+account-setup-calendars-button = Calendrau
+account-setup-connect-link = Cysylltu
+account-setup-existing-address-book = Wedi'u cysylltu
+    .title = Llyfr cyfeiriadau wedi'u cysylltu'n barod
+account-setup-existing-calendar = Wedi'u cysylltu
+    .title = Calendrau wedi'u cysylltu'n barod
+account-setup-connect-all-calendars = Cysylltu'r holl galendrau
+account-setup-connect-all-address-books = Cysylltu'r holl lyfrau cyfeiriadau
+
+## Calendar synchronization dialog
+
+calendar-dialog-title = Cysylltu calendr
+calendar-dialog-cancel-button = Diddymu
+    .accesskey = D
+calendar-dialog-confirm-button = Cysylltu
+    .accesskey = C
+account-setup-calendar-name-label = Enw
+account-setup-calendar-name-input =
+    .placeholder = Calendr
+account-setup-calendar-color-label = Lliw
+account-setup-calendar-refresh-label = Adnewyddu
+account-setup-calendar-refresh-manual = Gyda Llaw
+# Variables:
+# $count (Number) - Number of minutes in the calendar refresh interval.
+account-setup-calendar-refresh-interval =
+    { $count ->
+        [zero] Byth
+        [one] Pob munud
+        [two] Pob { $count } funud
+        [few] Pob { $count } munud
+        [many] Pob { $count } munud
+       *[other] Pob { $count } munud
+    }
+account-setup-calendar-read-only = Darllen yn unig
+    .accesskey = D
+account-setup-calendar-show-reminders = Dangos Atgoffwyr
+    .accesskey = A
+account-setup-calendar-offline-support = Cefnogaeth All-lein
+    .accesskey = A
diff --git a/thunderbird-l10n/cy/localization/cy/messenger/addonNotifications.ftl b/thunderbird-l10n/cy/localization/cy/messenger/addonNotifications.ftl
new file mode 100644
index 0000000000..b5432c0d34
--- /dev/null
+++ b/thunderbird-l10n/cy/localization/cy/messenger/addonNotifications.ftl
@@ -0,0 +1,142 @@
+# This Source Code Form is subject to the terms of the Mozilla Public
+# License, v. 2.0. If a copy of the MPL was not distributed with this
+# file, You can obtain one at http://mozilla.org/MPL/2.0/.
+
+xpinstall-prompt = Rhwystrodd { -brand-short-name } y wefan rhag gofyn i chi osod meddalwedd ar eich cyfrifiadur.
+
+## Variables:
+##   $host (String): The hostname of the site the add-on is being installed from.
+
+xpinstall-prompt-header = Caniatáu i { $host } osod ategyn?
+xpinstall-prompt-message = Rydych yn ceisio gosod ychwanegyn o { $host }. Gwnewch yn siŵr eich bod yn ymddiried yn y wefan hon cyn parhau.
+
+##
+
+xpinstall-prompt-header-unknown = Caniatáu i wefan anhysbys osod ategyn?
+xpinstall-prompt-message-unknown = Rydych yn ceisio gosod ychwanegyn o wefan anhysbys. Gwnewch yn siŵr eich bod yn ymddiried yn y wefan hon cyn parhau.
+xpinstall-prompt-dont-allow =
+    .label = Peidio â Chaniatáu
+    .accesskey = P
+xpinstall-prompt-never-allow =
+    .label = Byth Caniatáu
+    .accesskey = B
+# Long text in this context make the dropdown menu extend awkwardly to the left,
+# avoid a localization that's significantly longer than the English version.
+xpinstall-prompt-never-allow-and-report =
+    .label = Adrodd am Wefan Amheus
+    .accesskey = A
+# Accessibility Note:
+# Be sure you do not choose an accesskey that is used elsewhere in the active context (e.g. main menu bar, submenu of the warning popup button)
+# See https://website-archive.mozilla.org/www.mozilla.org/access/access/keyboard/ for details
+xpinstall-prompt-install =
+    .label = Ymlaen i'r Gosod
+    .accesskey = Y
+
+# These messages are shown when a website invokes navigator.requestMIDIAccess.
+
+site-permission-install-first-prompt-midi-header = Mae'r wefan hon yn gofyn am fynediad i'ch dyfeisiau MIDI (Rhyngwyneb Digidol Offeryn Cerdd). Mae modd galluogi mynediad i ddyfais trwy osod ychwanegyn.
+site-permission-install-first-prompt-midi-message = Does dim gwarant fod y mynediad hwn yn ddiogel. Parhewch dim ond os ydych yn ymddiried yn y wefan hon.
+
+##
+
+xpinstall-disabled-locked = Mae gosod meddalwedd wedi ei analluogi gan eich gweinyddwr system.
+xpinstall-disabled = Mae gosod meddalwedd wedi ei analluogi. Cliciwch Galluogi a cheisio eto.
+xpinstall-disabled-button =
+    .label = Galluogi
+    .accesskey = G
+# This message is shown when the installation of an add-on is blocked by enterprise policy.
+# Variables:
+#   $addonName (String): the name of the add-on.
+#   $addonId (String): the ID of add-on.
+addon-install-blocked-by-policy = Mae { $addonName } ({ $addonId }) wedi ei rwystro gan eich gweinyddwr system.
+# This message is shown when the installation of add-ons from a domain is blocked by enterprise policy.
+addon-domain-blocked-by-policy = Rhwystrodd eich gweinyddwr systemau y wefan hon rhag gofyn i chi osod meddalwedd ar eich cyfrifiadur.
+addon-install-full-screen-blocked = Nid yw gosod ychwanegion yn cael ei ganiatáu cyn mynd neu wrth fynd i'r modd sgrin lawn.
+# Variables:
+#   $addonName (String): the localized name of the sideloaded add-on.
+webext-perms-sideload-menu-item = { $addonName } wedi ei ychwanegu i { -brand-short-name }
+# Variables:
+#   $addonName (String): the localized name of the extension which has been updated.
+webext-perms-update-menu-item = Mae { $addonName } angen caniatâd newydd
+
+## Add-on removal warning
+
+# Variables:
+#  $name (String): The name of the add-on that will be removed.
+addon-removal-title = Tynnu { $name }?
+# Variables:
+#   $name (String): the name of the extension which is about to be removed.
+addon-removal-message = Tynnu { $name } o { -brand-shorter-name }?
+addon-removal-button = Tynnu
+addon-removal-abuse-report-checkbox = Adroddwch am yr estyniad hwn i { -vendor-short-name }
+# Variables:
+#   $addonCount (Number): the number of add-ons being downloaded
+addon-downloading-and-verifying =
+    { $addonCount ->
+        [zero] Llwytho i lawr a dilysu { $addonCount } ychwanegion…
+        [one] Llwytho i lawr a dilysu { $addonCount } ychwanegyn…
+        [two] Llwytho i lawr a dilysu { $addonCount } ychwanegyn…
+        [few] Llwytho i lawr a dilysu { $addonCount } ychwanegyn…
+        [many] Llwytho i lawr a dilysu { $addonCount } ychwanegyn…
+       *[other] Llwytho i lawr a dilysu { $addonCount } ychwanegyn…
+    }
+addon-download-verifying = Dilysu
+addon-install-cancel-button =
+    .label = Diddymu
+    .accesskey = D
+addon-install-accept-button =
+    .label = Ychwanegu
+    .accesskey = Y
+
+## Variables:
+##   $addonCount (Number): the number of add-ons being installed
+
+addon-confirm-install-message =
+    { $addonCount ->
+        [zero] Hoffai'r wefan hon osod ychwanegyn yn { -brand-short-name }:
+        [one] Hoffai'r wefan hon osod { $addonCount } ychwanegyn yn { -brand-short-name }:
+        [two] Hoffai'r wefan hon osod { $addonCount } ychwanegyn yn { -brand-short-name }:
+        [few] Hoffai'r wefan hon osod { $addonCount } ychwanegyn yn { -brand-short-name }:
+        [many] Hoffai'r wefan hon osod { $addonCount } ychwanegyn yn { -brand-short-name }:
+       *[other] Hoffai'r wefan hon osod { $addonCount } ychwanegyn yn { -brand-short-name }:
+    }
+addon-confirm-install-unsigned-message =
+    { $addonCount ->
+        [zero] Rhybudd: Hoffai'r wefan hon osod ychwanegion heb eu gwirio yn { -brand-short-name }. Mentrwch ar eich risg eich hun.
+        [one] Rhybudd: Hoffai'r wefan hon osod ychwanegyn heb ei wirio yn { -brand-short-name }. Mentrwch ar eich risg eich hun.
+        [two] Rhybudd: Hoffai'r wefan hon osod ychwanegion heb eu gwirio yn { -brand-short-name }. Mentrwch ar eich risg eich hun.
+        [few] Rhybudd: Hoffai'r wefan hon osod ychwanegion heb eu gwirio yn { -brand-short-name }. Mentrwch ar eich risg eich hun.
+        [other] Rhybudd: Hoffai'r wefan hon osod ychwanegion heb eu gwirio yn { -brand-short-name }. Mentrwch ar eich risg eich hun.
+       *[many] Rhybudd: Hoffai'r wefan hon osod ychwanegion heb eu gwirio yn { -brand-short-name }. Mentrwch ar eich risg eich hun.
+    }
+# Variables:
+#   $addonCount (Number): the number of add-ons being installed (at least 2)
+addon-confirm-install-some-unsigned-message =
+    { $addonCount ->
+        [zero] Rhybudd: Hoffai'r wefan hon osod ychwanegion heb eu gwirio yn { -brand-short-name }. Mentrwch ar eich risg eich hun.
+        [one] Rhybudd: Hoffai'r wefan hon osod { $addonCount } ychwanegyn yn { -brand-short-name }, mae rhai ohonynt heb eu gwirio. Gwnewch hyn ar eich menter eich hun.
+        [two] Rhybudd: Hoffai'r wefan hon osod { $addonCount } ychwanegyn yn { -brand-short-name }, mae rhai ohonynt heb eu gwirio. Gwnewch hyn ar eich menter eich hun.
+        [few] Rhybudd: Hoffai'r wefan hon osod { $addonCount } ychwanegyn yn { -brand-short-name }, mae rhai ohonynt heb eu gwirio. Gwnewch hyn ar eich menter eich hun.
+        [many] Rhybudd: Hoffai'r wefan hon osod { $addonCount } ychwanegyn yn { -brand-short-name }, mae rhai ohonynt heb eu gwirio. Gwnewch hyn ar eich menter eich hun.
+       *[other] Rhybudd: Hoffai'r wefan hon osod { $addonCount } ychwanegyn yn { -brand-short-name }, mae rhai ohonynt heb eu gwirio. Gwnewch hyn ar eich menter eich hun.
+    }
+
+## Add-on install errors
+## Variables:
+##   $addonName (String): the add-on name.
+
+addon-install-error-network-failure = Nid oedd modd llwytho'r ychwanegyn i lawr oherwydd methiant y cysylltiad.
+addon-install-error-incorrect-hash = Nid oedd modd gosod yr ychwanegyn am nad yw'n cydweddu â'r ychwanegyn roedd { -brand-short-name } yn ei ddisgwyl.
+addon-install-error-corrupt-file = Nid oedd modd llwytho'r ychwanegyn i lawr o'r wefan hon oherwydd ei fod yn ymddangos yn llwgr.
+addon-install-error-file-access = Nid oedd modd gosod { $addonName } gan nad oedd { -brand-short-name } yn gallu newid y linell angenrheidiol.
+addon-install-error-not-signed = Mae { -brand-short-name } wedi atal y wefan rhag gosod ychwanegyn sydd heb ei wirio.
+addon-install-error-invalid-domain = Nid oes modd gosod yr ychwanegyn { $addonName } o'r lleoliad hwn.
+addon-local-install-error-network-failure = Nid oedd modd gosod yr ychwanegyn oherwydd gwall system.
+addon-local-install-error-incorrect-hash = Nid oedd modd gosod yr ychwanegyn am nad yw'n cydweddu â'r ychwanegyn { -brand-short-name } disgwyliwyd.
+addon-local-install-error-corrupt-file = Nid oedd modd gosod yr ychwanegyn am ei fod yn edrych yn llwgr.
+addon-local-install-error-file-access = Nid oedd modd gosod { $addonName } gan nad oedd { -brand-short-name } yn gallu newid y linell angenrheidiol.
+addon-local-install-error-not-signed = Nid oedd modd gosod yr ychwanegyn am nad yw wedi ei wirio.
+# Variables:
+#   $appVersion (String): the application version.
+addon-install-error-incompatible = Nid oedd modd gosod { $addonName } am nad yw'n cydweddu â { -brand-short-name } { $appVersion }.
+addon-install-error-blocklisted = Nid oedd modd gosod { $addonName } am fod risg uchel iddo achosi problemau sefydlogrwydd a diogelwch.
diff --git a/thunderbird-l10n/cy/localization/cy/messenger/addressbook/abCardDAVDialog.ftl b/thunderbird-l10n/cy/localization/cy/messenger/addressbook/abCardDAVDialog.ftl
new file mode 100644
index 0000000000..f2f42115dc
--- /dev/null
+++ b/thunderbird-l10n/cy/localization/cy/messenger/addressbook/abCardDAVDialog.ftl
@@ -0,0 +1,26 @@
+# This Source Code Form is subject to the terms of the Mozilla Public
+# License, v. 2.0. If a copy of the MPL was not distributed with this
+# file, you can obtain one at http://mozilla.org/MPL/2.0/.
+
+carddav-window-title = Llyfr Cyfeiriadau CardDAV Newydd
+
+carddav-dialog =
+    .buttonlabelaccept = Parhau
+    .buttonaccesskeyaccept = P
+
+carddav-username-label =
+    .value = Enw Defnyddiwr:
+    .accesskey = E
+carddav-location-label =
+    .value = Lleoliad:
+    .accesskey = L
+carddav-location =
+    .default-placeholder = URL neu enw gwesteiwr gweinydd y llyfr cyfeiriadau
+
+carddav-loading = Chwilio am y ffurfweddiad…
+carddav-known-incompatible = Mae'n hysbys bod { $url } yn anghydnaws â { -brand-short-name }.
+carddav-connection-error = Methu cysylltu.
+carddav-none-found = Heb ddod o hyd i lyfrau cyfeiriadau i'w hychwanegu ar gyfer y cyfrif penodedig.
+carddav-already-added = Mae'r holl lyfrau cyfeiriadau ar gyfer y cyfrif penodol eisoes wedi'u hychwanegu.
+
+carddav-available-books = Llyfrau cyfeiriadau sydd ar gael:
diff --git a/thunderbird-l10n/cy/localization/cy/messenger/addressbook/abCardDAVProperties.ftl b/thunderbird-l10n/cy/localization/cy/messenger/addressbook/abCardDAVProperties.ftl
new file mode 100644
index 0000000000..1b28ae181e
--- /dev/null
+++ b/thunderbird-l10n/cy/localization/cy/messenger/addressbook/abCardDAVProperties.ftl
@@ -0,0 +1,37 @@
+# This Source Code Form is subject to the terms of the Mozilla Public
+# License, v. 2.0. If a copy of the MPL was not distributed with this
+# file, you can obtain one at http://mozilla.org/MPL/2.0/.
+
+carddav-url-label =
+    .value = URL CardDAV:
+    .accesskey = V
+carddav-refreshinterval-label =
+    .label = Cydweddu:
+    .accesskey = C
+# Variables:
+#   $minutes (integer) - Number of minutes between address book synchronizations
+carddav-refreshinterval-minutes-value =
+    .label =
+        { $minutes ->
+            [zero] pob munud
+            [one] pob munud
+            [two] pob { $minutes } funud
+            [few] pob { $minutes } munud
+            [many] pob { $minutes } munud
+           *[other] pob { $minutes } munud
+        }
+# Variables:
+#   $hours (integer) - Number of hours between address book synchronizations
+carddav-refreshinterval-hours-value =
+    .label =
+        { $hours ->
+            [zero] pob awr
+            [one] pob awr
+            [two] pob { $hours } awr
+            [few] pob { $hours } awr
+            [many] pob { $hours } awr
+           *[other] pob { $hours } awr
+        }
+carddav-readonly-label =
+    .label = Darllen-yn-unig
+    .accesskey = D
diff --git a/thunderbird-l10n/cy/localization/cy/messenger/addressbook/aboutAddressBook.ftl b/thunderbird-l10n/cy/localization/cy/messenger/addressbook/aboutAddressBook.ftl
new file mode 100644
index 0000000000..807d15e162
--- /dev/null
+++ b/thunderbird-l10n/cy/localization/cy/messenger/addressbook/aboutAddressBook.ftl
@@ -0,0 +1,367 @@
+# This Source Code Form is subject to the terms of the Mozilla Public
+# License, v. 2.0. If a copy of the MPL was not distributed with this
+# file, you can obtain one at http://mozilla.org/MPL/2.0/.
+
+about-addressbook-title = Llyfr Cyfeiriadau
+
+## Toolbar
+
+about-addressbook-toolbar-new-address-book =
+    .label = Llyfr Cyfeiriadau Newydd
+about-addressbook-toolbar-add-carddav-address-book =
+    .label = Ychwanegu Llyfr Cyfeiriadau CardDAV
+about-addressbook-toolbar-add-ldap-address-book =
+    .label = Ychwanegu Llyfr Cyfeiriadau LDAP
+about-addressbook-toolbar-new-contact =
+    .label = Cysylltiad Newydd
+about-addressbook-toolbar-new-list =
+    .label = Rhestr Newydd
+about-addressbook-toolbar-import =
+    .label = Mewnforio
+
+## Books
+
+all-address-books-row =
+    .title = Pob Llyfr Cyfeiriadau
+all-address-books = Pob Llyfr Cyfeiriadau
+# Variables:
+# $name (String) - The name of the selected book/list.
+# $count (Number) - The number of contacts in the selected book/list.
+about-addressbook-card-count = Cyfanswm y cysylltiadau yn { $name } : { $count }
+# Variables:
+# $count (Number) - The number of contacts in all address books.
+about-addressbook-card-count-all = Cyfanswm y cysylltiadau yn { $name } : { $count }
+about-addressbook-books-context-properties =
+    .label = Priodweddau
+about-addressbook-books-context-edit-list =
+    .label = Golygu'r rhestr
+about-addressbook-books-context-synchronize =
+    .label = Cydweddu
+about-addressbook-books-context-edit =
+    .label = Golygu
+about-addressbook-books-context-print =
+    .label = Argraffu…
+about-addressbook-books-context-export =
+    .label = Allforio…
+about-addressbook-books-context-delete =
+    .label = Dileu
+about-addressbook-books-context-remove =
+    .label = Tynnu
+about-addressbook-books-context-startup-default =
+    .label = Cyfarwyddiadur cychwyn rhagosodedig
+about-addressbook-confirm-delete-book-title = Dileu Llyfr Cyfeiriadau
+# Variables:
+# $name (String) - Name of the address book to be deleted.
+about-addressbook-confirm-delete-book = Ydych chi'n siŵr eich bod chi am ddileu { $name } a'i holl gysylltiadau?
+about-addressbook-confirm-remove-remote-book-title = Dileu Llyfr Cyfeiriadau
+# Variables:
+# $name (String) - Name of the remote address book to be removed.
+about-addressbook-confirm-remove-remote-book = Ydych chi'n siŵr eich bod chi am dynnu { $name }?
+
+## Cards
+
+# Variables:
+# $name (String) - Name of the address book that will be searched.
+about-addressbook-search =
+    .placeholder = Chwilio { $name }
+about-addressbook-search-all =
+    .placeholder = Chwilio'r holl lyfrau cyfeiriadau
+about-addressbook-sort-button2 =
+    .title = Rhestru dewisiadau dangos
+about-addressbook-name-format-display =
+    .label = Enw Dangos
+about-addressbook-name-format-firstlast =
+    .label = Cyntaf Olaf
+about-addressbook-name-format-lastfirst =
+    .label = Olaf, Cyntaf
+about-addressbook-sort-name-ascending =
+    .label = Trefnu yn ôl enw (A > Z)
+about-addressbook-sort-name-descending =
+    .label = Trefnu yn ôl enw (Z > A)
+about-addressbook-sort-email-ascending =
+    .label = Trefnu yn ôl cyfeiriad e-bost (A > Z)
+about-addressbook-sort-email-descending =
+    .label = Trefnu yn ôl cyfeiriad e-bost (Z > A)
+about-addressbook-horizontal-layout =
+    .label = Newid i gynllun llorweddol
+about-addressbook-vertical-layout =
+    .label = Newid i gynllun llorweddol
+about-addressbook-table-layout =
+    .label = Cynllun tabl
+
+## Card column headers
+## Each string is listed here twice, and the values should match.
+
+about-addressbook-column-header-generatedname = Enw
+about-addressbook-column-label-generatedname =
+    .label = { about-addressbook-column-header-generatedname }
+about-addressbook-column-header-emailaddresses = Cyfeiriadau E-bost
+about-addressbook-column-label-emailaddresses =
+    .label = { about-addressbook-column-header-emailaddresses }
+about-addressbook-column-header-phonenumbers = Rhifau Ffôn
+about-addressbook-column-label-phonenumbers =
+    .label = { about-addressbook-column-header-phonenumbers }
+about-addressbook-column-header-addresses = Cyfeiriadau
+about-addressbook-column-label-addresses =
+    .label = { about-addressbook-column-header-addresses }
+about-addressbook-column-header-title = Teitl
+about-addressbook-column-label-title =
+    .label = { about-addressbook-column-header-title }
+about-addressbook-column-header-department = Adran
+about-addressbook-column-label-department =
+    .label = { about-addressbook-column-header-department }
+about-addressbook-column-header-organization = Corff
+about-addressbook-column-label-organization =
+    .label = { about-addressbook-column-header-organization }
+about-addressbook-column-header-addrbook = Llyfr Cyfeiriadau
+about-addressbook-column-label-addrbook =
+    .label = { about-addressbook-column-header-addrbook }
+about-addressbook-column-header-generatedname2 = Enw
+    .title = Trefnu yn ôl enwau
+about-addressbook-column-label-generatedname2 =
+    .label = Enw
+about-addressbook-column-header-emailaddresses2 = Cyfeiriadau E-bost
+    .title = Trefnu yn ôl cyfeiriadau e-byst
+about-addressbook-column-label-emailaddresses2 =
+    .label = Cyfeiriadau E-bost
+about-addressbook-column-header-nickname2 = Llysenw
+    .title = Trefnu yn ôl llysenwau
+about-addressbook-column-label-nickname2 =
+    .label = Llysenw
+about-addressbook-column-header-phonenumbers2 = Rhifau Ffôn
+    .title = Trefnu yn ôl rhifau ffôn
+about-addressbook-column-label-phonenumbers2 =
+    .label = Rhifau Ffôn
+about-addressbook-column-header-addresses2 = Cyfeiriadau
+    .title = Trefnu yn ôl cyfeiriadau
+about-addressbook-column-label-addresses2 =
+    .label = Cyfeiriadau
+about-addressbook-column-header-title2 = Teitl
+    .title = Trefnu yn ôl teitl
+about-addressbook-column-label-title2 =
+    .label = Teitl
+about-addressbook-column-header-department2 = Adran
+    .title = Trefnu yn ôl adrannau
+about-addressbook-column-label-department2 =
+    .label = Adran
+about-addressbook-column-header-organization2 = Corff
+    .title = Trefnu yn ôl cyrff
+about-addressbook-column-label-organization2 =
+    .label = Corff
+about-addressbook-column-header-addrbook2 = Llyfr Cyfeiriadau
+    .title = Trefnu yn ôl llyfrau cyfeiriadau
+about-addressbook-column-label-addrbook2 =
+    .label = Llyfr Cyfeiriadau
+about-addressbook-cards-context-write =
+    .label = Ysgrifennu
+about-addressbook-confirm-delete-mixed-title = Dileu Cysylltiadau a Rhestrau
+# Variables:
+# $count (Number) - The number of contacts and lists to be deleted. Always greater than 1.
+about-addressbook-confirm-delete-mixed = Ydych chi'n siŵr eich bod chi am ddileu'r { $count } cysylltiad a'r rhestrau hyn?
+# Variables:
+# $count (Number) - The number of lists to be deleted.
+about-addressbook-confirm-delete-lists-title =
+    { $count ->
+        [zero] Dileu Rhestrau
+        [one] Dileu Rhestr
+        [two] Dileu Rhestr
+        [few] Dileu Rhestr
+        [many] Dileu Rhestr
+       *[other] Dileu Rhestr
+    }
+# Variables:
+# $count (Number) - The number of lists to be deleted.
+# $name (String) - The name of the list to be deleted, if $count is 1.
+about-addressbook-confirm-delete-lists =
+    { $count ->
+        [zero] Ydych chi'n siŵr eich bod eisiau dileu'r cysylltiad { $name }?
+        [one] Ydych chi'n siŵr eich bod eisiau dileu'r cysylltiad { $name }?
+        [two] Ydych chi'n siŵr eich bod eisiau dileu'r cysylltiad { $name }?
+        [few] Ydych chi'n siŵr eich bod eisiau dileu'r cysylltiad { $name }?
+        [many] Ydych chi'n siŵr eich bod eisiau dileu'r cysylltiad { $name }?
+       *[other] Ydych chi'n siŵr eich bod eisiau dileu'r cysylltiad { $name }?
+    }
+# Variables:
+# $count (Number) - The number of contacts to be removed.
+about-addressbook-confirm-remove-contacts-title =
+    { $count ->
+        [zero] Tynnu Cysylltiad
+        [one] Tynnu Cysylltiad
+        [two] Tynnu Cysylltiad
+        [few] Tynnu Cysylltiad
+        [many] Tynnu Cysylltiad
+       *[other] Tynnu Cysylltiad
+    }
+# Variables:
+# $count (Number) - The number of contacts to be removed.
+# $name (String) - The name of the contact to be removed, if $count is 1.
+# $list (String) - The name of the list that contacts will be removed from.
+about-addressbook-confirm-remove-contacts =
+    { $count ->
+        [zero] Ydych chi'n siŵr eich bod eisiau tynnu'r cysylltiad { $name } o { $list }?
+        [one] Ydych chi'n siŵr eich bod eisiau tynnu'r cysylltiad { $name } o { $list }?
+        [two] Ydych chi'n siŵr eich bod eisiau tynnu'r cysylltiad { $name } o { $list }?
+        [few] Ydych chi'n siŵr eich bod eisiau tynnu'r cysylltiad { $name } o { $list }?
+        [many] Ydych chi'n siŵr eich bod eisiau tynnu'r cysylltiad { $name } o { $list }?
+       *[other] Ydych chi'n siŵr eich bod eisiau tynnu'r cysylltiad { $name } o { $list }?
+    }
+# Variables:
+# $name (String) - The name of the contact to be removed.
+# $list (String) - The name of the list that contacts will be removed from.
+about-addressbook-confirm-remove-contacts-single = Ydych chi'n siŵr eich bod am ddileu { $name } o { $list }?
+# Variables:
+# $count (Number) - The number of contacts to be removed.
+# $list (String) - The name of the list that contacts will be removed from.
+about-addressbook-confirm-remove-contacts-multi =
+    { $count ->
+        [zero] Ydych chi'n siŵr eich bod eisiau tynnu'r { $count } cysylltiadau o { $list }?
+        [one] Ydych chi'n siŵr eich bod eisiau tynnu'r { $count } cysylltiad o { $list }?
+        [two] Ydych chi'n siŵr eich bod eisiau tynnu'r { $count } gysylltiad o { $list }?
+        [few] Ydych chi'n siŵr eich bod eisiau tynnu'r { $count } cysylltiad o { $list }?
+        [many] Ydych chi'n siŵr eich bod eisiau tynnu'r { $count } chysylltiad o { $list }?
+       *[other] Ydych chi'n siŵr eich bod eisiau tynnu'r { $count } cysylltiad o { $list }?
+    }
+# Variables:
+# $count (Number) - The number of contacts to be deleted.
+about-addressbook-confirm-delete-contacts-title =
+    { $count ->
+        [zero] Dileu Cysylltiadau
+        [one] Dileu Cysylltiad
+        [two] Dileu Cysylltiad
+        [few] Dileu Cysylltiad
+        [many] Dileu Cysylltiad
+       *[other] Dileu Cysylltiad
+    }
+# Variables:
+# $count (Number) - The number of contacts to be deleted.
+# $name (String) - The name of the contact to be deleted, if $count is 1.
+about-addressbook-confirm-delete-contacts =
+    { $count ->
+        [zero] Ydych chi'n siŵr eich bod chi am ddileu'r { $count } cysylltiad yma?
+        [one] Ydych chi'n siŵr eich bod chi am ddileu'r { $count } cysylltiad yma?
+        [two] Ydych chi'n siŵr eich bod chi am ddileu'r { $count } cysylltiad yma?
+        [few] Ydych chi'n siŵr eich bod chi am ddileu'r { $count } cysylltiad yma?
+        [many] Ydych chi'n siŵr eich bod chi am ddileu'r { $count } cysylltiad yma?
+       *[other] Ydych chi'n siŵr eich bod chi am ddileu'r { $count } cysylltiad yma?
+    }
+# Variables:
+# $name (String) - The name of the contact to be deleted.
+about-addressbook-confirm-delete-contacts-single = Ydych chi'n siŵr eich bod am ddileu'r cyswllt { $name }?
+# Variables:
+# $count (Number) - The number of contacts to be deleted.
+about-addressbook-confirm-delete-contacts-multi =
+    { $count ->
+        [zero] Ydych chi'n siŵr eich bod chi am ddileu'r { $count } cysylltiadau hyn?
+        [one] Ydych chi'n siŵr eich bod chi am ddileu'r { $count } cysylltiad yma?
+        [two] Ydych chi'n siŵr eich bod chi am ddileu'r { $count } gysylltiad yma?
+        [few] Ydych chi'n siŵr eich bod chi am ddileu'r { $count } cysylltiad yma?
+        [many] Ydych chi'n siŵr eich bod chi am ddileu'r { $count } chysylltiad yma?
+       *[other] Ydych chi'n siŵr eich bod chi am ddileu'r { $count } cysylltiad yma?
+    }
+
+## Card list placeholder
+## Shown when there are no cards in the list
+
+about-addressbook-placeholder-empty-book = Dim cysylltiadau ar gael
+about-addressbook-placeholder-new-contact = Cysylltiad Newydd
+about-addressbook-placeholder-search-only = Dim ond ar ôl chwilio mae'r llyfr cyfeiriadau hwn yn dangos cysylltiadau
+about-addressbook-placeholder-searching = Yn chwilio…
+about-addressbook-placeholder-no-search-results = Heb ganfod cysylltiadau
+
+## Details
+
+# Variables:
+# $count (Number) - The number of selected items (will never be fewer than two)
+about-addressbook-selection-mixed-header = Mae { $count } o gysylltiadau a rhestrau wedi'u dewis
+# Variables:
+# $count (Number) - The number of selected contacts
+about-addressbook-selection-contacts-header = Mae { $count } cysylltiad wedi'u dewis
+# Variables:
+# $count (Number) - The number of selected lists
+about-addressbook-selection-lists-header = Mae { $count } rhestr wedi'u dewis
+# Variables:
+# $count (Number) - The number of selected items (will never be fewer than 2).
+about-addressbook-selection-mixed-header2 =
+    { $count ->
+        [zero] Mae { $count } cofnodion llyfr cyfeiriadau wedi'u dewis
+        [one] Mae { $count } cofnod llyfr cyfeiriadau wedi'i ddewis
+        [two] Mae { $count } gofnod llyfr cyfeiriadau wedi'u dewis
+        [few] Mae { $count } cofnod llyfr cyfeiriadau wedi'u dewis
+        [many] Mae { $count } chofnod llyfr cyfeiriadau wedi'u dewis
+       *[other] Mae { $count } cofnod llyfr cyfeiriadau wedi'u dewis
+    }
+# Variables:
+# $count (Number) - The number of selected contacts
+about-addressbook-selection-contacts-header2 =
+    { $count ->
+        [zero] Mae { $count } cysylltiad wedi'u dewis
+        [one] Mae { $count } cyswllt wedi'i ddewis
+        [two] Mae { $count } gysylltiad wedi'u dewis
+        [few] Mae { $count } cysylltiad wedi'u dewis
+        [many] Mae { $count } chysylltiad wedi'u dewis
+       *[other] Mae { $count } cysylltiad wedi'u dewis
+    }
+# Variables:
+# $count (Number) - The number of selected lists
+about-addressbook-selection-lists-header2 =
+    { $count ->
+        [zero] Does { $count } rhestrau wedi'u dewis
+        [one] Mae { $count } rhestr wedi'i ddewis
+        [two] Mae { $count } restr wedi'u dewis
+        [few] Mae { $count } restr wedi'u dewis
+        [many] Mae { $count } rhestr wedi'u dewis
+       *[other] Mae { $count } rhestr wedi'u dewis
+    }
+about-addressbook-details-edit-photo =
+    .title = Golygu llun cyswllt
+about-addressbook-new-contact-header = Cysylltiad Newydd
+about-addressbook-prefer-display-name = Dewis enw dangos o flaen pennyn neges
+about-addressbook-write-action-button = Ysgrifennu
+about-addressbook-event-action-button = Digwyddiad
+about-addressbook-search-action-button = Chwilio
+about-addressbook-new-list-action-button = Rhestr Newydd
+about-addressbook-begin-edit-contact-button = Golygu
+about-addressbook-delete-edit-contact-button = Dileu
+about-addressbook-cancel-edit-contact-button = Diddymu
+about-addressbook-save-edit-contact-button = Cadw
+about-addressbook-add-contact-to = Ychwanegu at:
+about-addressbook-details-email-addresses-header = Cyfeiriadau E-bost
+about-addressbook-details-phone-numbers-header = Rhifau Ffôn
+about-addressbook-details-addresses-header = Cyfeiriadau
+about-addressbook-details-notes-header = Nodiadau
+about-addressbook-details-impp-header = Negesu Chwim
+about-addressbook-details-websites-header = Gwefannau
+about-addressbook-details-other-info-header = Manylion Eraill
+about-addressbook-entry-type-work = Gwaith
+about-addressbook-entry-type-home = Cartref
+about-addressbook-entry-type-fax = Ffacs
+# Or "Mobile"
+about-addressbook-entry-type-cell = Symudol
+about-addressbook-entry-type-pager = Swnyn
+about-addressbook-entry-name-birthday = Pen-blwydd
+about-addressbook-entry-name-anniversary = Dathliad
+about-addressbook-entry-name-title = Teitl
+about-addressbook-entry-name-role = Rôl
+about-addressbook-entry-name-organization = Corff
+about-addressbook-entry-name-website = Gwefan
+about-addressbook-entry-name-time-zone = Cylch Amser
+about-addressbook-entry-name-custom1 = Cyfaddasu 1
+about-addressbook-entry-name-custom2 = Cyfaddasu 2
+about-addressbook-entry-name-custom3 = Cyfaddasu 3
+about-addressbook-entry-name-custom4 = Cyfaddasu 4
+about-addressbook-unsaved-changes-prompt-title = Newidiadau heb eu Cadw
+about-addressbook-unsaved-changes-prompt = Ydych chi am gadw'ch newidiadau cyn gadael y wedd golygu?
+
+# Photo dialog
+
+about-addressbook-photo-drop-target = Gollwng neu gludo llun yma, neu glicio i ddewis ffeil.
+about-addressbook-photo-drop-loading = Yn llwytho llun…
+about-addressbook-photo-drop-error = Wedi methu llwytho llun.
+about-addressbook-photo-filepicker-title = Dewiswch ffeil delwedd
+about-addressbook-photo-discard = Dileu'r llun presennol
+about-addressbook-photo-cancel = Diddymu
+about-addressbook-photo-save = Cadw
+
+# Keyboard shortcuts
+
+about-addressbook-new-contact-key = N
diff --git a/thunderbird-l10n/cy/localization/cy/messenger/addressbook/fieldMapImport.ftl b/thunderbird-l10n/cy/localization/cy/messenger/addressbook/fieldMapImport.ftl
new file mode 100644
index 0000000000..bedd9e6bba
--- /dev/null
+++ b/thunderbird-l10n/cy/localization/cy/messenger/addressbook/fieldMapImport.ftl
@@ -0,0 +1,12 @@
+# This Source Code Form is subject to the terms of the Mozilla Public
+# License, v. 2.0. If a copy of the MPL was not distributed with this
+# file, You can obtain one at http://mozilla.org/MPL/2.0/.
+
+import-ab-csv-dialog-title = Mewnforio Llyfr Cyfeiriadau o Ffeil Testun
+
+#   $recordNumber (Number) - The current record number of the preview data.
+import-ab-csv-preview-record-number = Rhagolwg o'r mewnforio data ar gyfer cofnod { $recordNumber }
+
+import-ab-csv-dialog =
+    .buttonlabelaccept = Mewnforio
+    .buttonaccesskeyaccept = M
diff --git a/thunderbird-l10n/cy/localization/cy/messenger/addressbook/vcard.ftl b/thunderbird-l10n/cy/localization/cy/messenger/addressbook/vcard.ftl
new file mode 100644
index 0000000000..e769b68f07
--- /dev/null
+++ b/thunderbird-l10n/cy/localization/cy/messenger/addressbook/vcard.ftl
@@ -0,0 +1,138 @@
+# This Source Code Form is subject to the terms of the Mozilla Public
+# License, v. 2.0. If a copy of the MPL was not distributed with this
+# file, you can obtain one at http://mozilla.org/MPL/2.0/.
+
+
+# Display Name
+
+vcard-displayname = Enw dangos
+vcard-displayname-placeholder =
+    .placeholder = { vcard-displayname }
+
+# Type selection
+
+vcard-entry-type-label = Math
+vcard-entry-type-home = Cartref
+vcard-entry-type-work = Gwaith
+vcard-entry-type-none = Dim
+vcard-entry-type-custom = Cyfaddas
+
+# N vCard field
+
+vcard-name-header = Enw
+vcard-n-prefix = Rhagddodiad
+vcard-n-add-prefix =
+    .title = Ychwanegu rhagddodiad
+vcard-n-firstname = Enw cyntaf
+vcard-n-add-firstname =
+    .title = Ychwanegu enw cyntaf
+vcard-n-middlename = Enw canol
+vcard-n-add-middlename =
+    .title = Ychwanegu enw canol
+vcard-n-lastname = Enw olaf
+vcard-n-add-lastname =
+    .title = Ychwanegu enw olaf
+vcard-n-suffix = Ôl-ddodiad
+vcard-n-add-suffix =
+    .title = Ychwanegu ôl-ddodiad
+
+# Nickname
+
+vcard-nickname = Llysenw
+
+# Email vCard field
+
+vcard-email-header = Cyfeiriadau E-bost
+vcard-email-add = Ychwanegu cyfeiriad e-bost
+vcard-email-label = Cyfeiriad e-bost
+vcard-primary-email-label = Rhagosodiad
+
+# URL vCard field
+
+vcard-url-header = Gwefannau
+vcard-url-add = Ychwanegu gwefan
+vcard-url-label = Gwefan
+
+# Tel vCard field
+
+vcard-tel-header = Rhifau Ffôn
+vcard-tel-add = Ychwanegu rhif ffôn
+vcard-tel-label = Rhif ffôn
+# Or "Mobile"
+vcard-entry-type-cell = Symudol
+vcard-entry-type-fax = Ffacs
+vcard-entry-type-pager = Swnyn
+
+# TZ vCard field
+
+vcard-tz-header = Cylch Amser
+vcard-tz-add = Ychwanegu cylch amser
+
+# IMPP vCard field
+
+vcard-impp2-header = Negesu Chwim
+vcard-impp-add = Ychwanegu cyfrif sgwrsio
+vcard-impp-label = Cyfrif sgwrsio
+vcard-impp-select = Protocol
+vcard-impp-option-other = Arall
+vcard-impp-input-label = URI
+vcard-impp-input-title = URI ar gyfer negeseuon chwim
+
+# BDAY and ANNIVERSARY vCard field
+
+vcard-bday-anniversary-header = Dyddiadau Arbennig
+vcard-bday-anniversary-add = Ychwanegu dyddiad arbennig
+vcard-bday-label = Pen-blwydd
+vcard-anniversary-label = Dathliad
+vcard-date-day = Diwrnod
+vcard-date-month = Mis
+vcard-date-year = Blwyddyn
+
+# ADR vCard field
+
+vcard-adr-header = Cyfeiriadau
+vcard-adr-add = Ychwanegu cyfeiriad
+vcard-adr-label = Cyfeiriad
+vcard-adr-delivery-label = Label dosbarthu
+vcard-adr-street = Cyfeiriad stryd
+# Or "Locality"
+vcard-adr-locality = Tref/Dinas
+# Or "Region"
+vcard-adr-region = Sir/Talaith:
+# The term "ZIP code" only applies in USA. Most locales should use "Postal code" only.
+vcard-adr-code = Cod Post/ZIP:
+vcard-adr-country = Gwlad
+
+# NOTE vCard field
+
+vcard-note-header = Nodiadau
+vcard-note-add = Ychwanegu nodyn
+
+# TITLE, ROLE and ORGANIZATION vCard fields
+
+vcard-org-header = Adeiladau Sefydliadol
+vcard-org-add = Ychwanegu adeiladau sefydliadol
+vcard-org-title = Teitl
+vcard-org-title-input =
+    .title = Safle neu swydd
+    .placeholder = Tetl swydd
+vcard-org-role = Rôl
+vcard-org-role-input =
+    .title = Swyddogaeth neu ran yn cael ei chwarae mewn sefyllfa benodol
+    .placeholder = Rôl mewn project
+vcard-org-org = Corff
+vcard-org-org-input =
+    .title = Enw corfforaethol
+    .placeholder = Enw cwmni
+vcard-org-org-unit = Adran
+vcard-org-org-unit-input =
+    .title = Enw uned corfforaethol
+    .placeholder = Adran
+
+# Custom properties
+
+vcard-custom-header = Priodweddau Cyfaddas
+vcard-custom-add = Ychwanegu priodweddau cyfaddas
+vcard-remove-button-title =
+    .title = Tynnu
+vcard-remove-button = Tynnu
diff --git a/thunderbird-l10n/cy/localization/cy/messenger/appmenu.ftl b/thunderbird-l10n/cy/localization/cy/messenger/appmenu.ftl
new file mode 100644
index 0000000000..43ad4c9ca4
--- /dev/null
+++ b/thunderbird-l10n/cy/localization/cy/messenger/appmenu.ftl
@@ -0,0 +1,210 @@
+# This Source Code Form is subject to the terms of the Mozilla Public
+# License, v. 2.0. If a copy of the MPL was not distributed with this
+# file, You can obtain one at http://mozilla.org/MPL/2.0/.
+
+
+## Sync
+
+appmenu-sync-panel-title =
+    .title = Sync
+appmenu-signin-panel =
+    .label = Mewngofnodwch i Sync
+    .accesskey = S
+appmenu-sync-sync =
+    .value = Cydweddu Cyfrif
+    .accesskey = C
+appmenu-sync-manage =
+    .value = Rheoli Cyfrif
+    .accesskey = R
+appmenu-sync-account =
+    .value = example@example.com
+appmenu-sync-now =
+    .label = Cydweddu Nawr
+    .accesskey = N
+appmenu-sync-settings =
+    .label = Gosodiadau Sync
+    .accesskey = G
+appmenu-sync-sign-out =
+    .label = Allgofnodi…
+    .accesskey = A
+
+## New Account
+
+appmenu-new-account-panel-title =
+    .title = Cyfrif Newydd
+appmenu-new-account-panel =
+    .label = Cyfrif Newydd
+    .accesskey = C
+appmenu-create-new-mail-account =
+    .label = Cael E-bost Newydd
+    .accesskey = E
+appmenu-new-mail-account =
+    .label = E-bost Cyfredol
+    .accesskey = b
+appmenu-new-calendar =
+    .label = Calendr
+    .accesskey = a
+appmenu-new-chat-account =
+    .label = Sgwrsio
+    .accesskey = S
+appmenu-new-feed =
+    .label = Llif
+    .accesskey = L
+appmenu-new-newsgroup =
+    .label = Grŵp Newyddion
+    .accesskey = N
+
+## New Account / Address Book
+
+appmenu-newab-panel-title =
+    .title = Llyfr Cyfeiriadau Newydd
+appmenu-newab-panel =
+    .label = Llyfr Cyfeiriadau Newydd
+    .accesskey = L
+appmenu-new-addressbook =
+    .label = Llyfrau Cyfeiriadau Lleol
+    .accesskey = C
+appmenu-new-carddav =
+    .label = Llyfr Cyfeiriadau CardDAV…
+    .accesskey = D
+appmenu-new-ldap =
+    .label = Llyfr Cyfeiriadau LDAP
+    .accesskey = D
+
+## Create
+
+appmenu-create-panel-title =
+    .title = Creu
+appmenu-create-panel =
+    .label = Creu
+    .accesskey = C
+appmenu-create-message =
+    .label = Neges
+    .accesskey = N
+appmenu-create-event =
+    .label = Digwyddiad
+    .accesskey = D
+appmenu-create-task =
+    .label = Tasg
+    .accesskey = T
+appmenu-create-contact =
+    .label = Cysylltiad
+    .accesskey = y
+
+## Open
+
+appmenu-open-file-panel =
+    .label = Agor o Ffeil
+    .accesskey = A
+appmenu-open-file-panel-title =
+    .title = Agor o Ffeil
+appmenu-open-message =
+    .label = Neges…
+    .accesskey = N
+appmenu-open-calendar =
+    .label = Calendr…
+    .accesskey = C
+
+## View / Layout
+
+appmenu-view-panel-title =
+    .title = Golwg
+appmenu-view-panel =
+    .label = Golwg
+    .accesskey = G
+appmenuitem-toggle-thread-pane-header =
+    .label = Pennyn Rhestrau Negeseuon
+appmenu-font-size-value = Maint Ffont
+appmenu-mail-uidensity-value = Dwysedd
+appmenu-uidensity-compact =
+    .tooltiptext = Cywasgu
+appmenu-uidensity-default =
+    .tooltiptext = Rhagosodedig
+appmenu-uidensity-relaxed =
+    .tooltiptext = Llaes
+appmenuitem-font-size-enlarge =
+    .tooltiptext = Cynyddu Maint Ffont
+appmenuitem-font-size-reduce =
+    .tooltiptext = Lleihau Maint Ffont
+# Variables:
+# $size (String) - The current font size.
+appmenuitem-font-size-reset =
+    .label = { $size }px
+    .tooltiptext = Ailosod Maint Ffont
+
+## Tools
+
+appmenu-tools-panel-title =
+    .title = Offer
+appmenu-tools-panel =
+    .label = Offer
+    .accesskey = O
+appmenu-tools-import =
+    .label = Mewnforio
+    .accesskey = M
+appmenu-tools-export =
+    .label = Allforio
+    .accesskey = A
+appmenu-tools-message-search =
+    .label = Chwilio drwy'r Negeseuon
+    .accesskey = C
+appmenu-tools-message-filters =
+    .label = Hidlau Negeseuon
+    .accesskey = H
+appmenu-tools-download-manager =
+    .label = Rheolwr Llwythi
+    .accesskey = R
+appmenu-tools-activity-manager =
+    .label = Rheolwr Gweithgaredd
+    .accesskey = R
+appmenu-tools-dev-tools =
+    .label = Offer Datblygwyr
+    .accesskey = O
+
+## Help
+
+appmenu-help-panel-title =
+    .title = Cymorth
+appmenu-help-get-help =
+    .label = Derbyn Cymorth
+    .accesskey = D
+appmenu-help-explore-features =
+    .label = Edrych ar y Nodweddion
+    .accesskey = E
+appmenu-help-shortcuts =
+    .label = Llwybrau Byr Bysellfwrdd
+    .accesskey = L
+appmenu-help-get-involved =
+    .label = Ymunwch
+    .accesskey = Y
+appmenu-help-donation =
+    .label = Gwnewch Rodd
+    .accesskey = G
+appmenu-help-share-feedback =
+    .label = Rhannwch Syniadau ac Adborth…
+    .accesskey = R
+appmenu-help-enter-troubleshoot-mode2 =
+    .label = Y Modd Datrys Problemau…
+    .accesskey = M
+appmenu-help-exit-troubleshoot-mode2 =
+    .label = Diffodd y Modd Datrys Problemau
+    .accesskey = D
+appmenu-help-troubleshooting-info =
+    .label = Gwybodaeth am Ddatrys Problemau
+    .accesskey = G
+appmenu-help-about-product =
+    .label = Ynghylch { -brand-short-name }
+    .accesskey = Y
+
+## Application Update
+
+appmenuitem-banner-update-downloading =
+    .label = Llwytho diweddariad { -brand-shorter-name } i lawr
+appmenuitem-banner-update-available =
+    .label = Mae diweddariad ar gael — llwytho i lawr nawr
+appmenuitem-banner-update-manual =
+    .label = Mae diweddariad ar gael — llwytho i lawr nawr
+appmenuitem-banner-update-unsupported =
+    .label = Methu diweddaru — mae'r system yn anghydnaws
+appmenuitem-banner-update-restart =
+    .label = Mae diweddariad ar gael — ailgychwyn nawr
diff --git a/thunderbird-l10n/cy/localization/cy/messenger/chat-verifySession.ftl b/thunderbird-l10n/cy/localization/cy/messenger/chat-verifySession.ftl
new file mode 100644
index 0000000000..b1d162960b
--- /dev/null
+++ b/thunderbird-l10n/cy/localization/cy/messenger/chat-verifySession.ftl
@@ -0,0 +1,17 @@
+# This Source Code Form is subject to the terms of the Mozilla Public
+# License, v. 2.0. If a copy of the MPL was not distributed with this
+# file, You can obtain one at http://mozilla.org/MPL/2.0/.
+
+verify-window-title = Gwirio Hunaniaeth
+
+# Variables:
+#   $subject (String) - a human readable identifier for the other side of the verification flow.
+verify-window-subject-title = Gwirio Hunaniaeth { $subject }
+
+verify-dialog =
+    .buttonlabelaccept = Cydweddiad
+    .buttonaccesskeyaccept = C
+    .buttonlabelextra2 = Dim Cyweddiad
+    .buttonaccesskeyextra2 = D
+
+challenge-label = Gwiriwch fod y llinyn sy'n cael ei ddangos yn cyd-fynd â'r hyn sy'n cael ei ddangos ar y pen draw.
diff --git a/thunderbird-l10n/cy/localization/cy/messenger/chat.ftl b/thunderbird-l10n/cy/localization/cy/messenger/chat.ftl
new file mode 100644
index 0000000000..035b730427
--- /dev/null
+++ b/thunderbird-l10n/cy/localization/cy/messenger/chat.ftl
@@ -0,0 +1,47 @@
+# This Source Code Form is subject to the terms of the Mozilla Public
+# License, v. 2.0. If a copy of the MPL was not distributed with this
+# file, You can obtain one at http://mozilla.org/MPL/2.0/.
+
+chat-joining-chat-icon2 =
+    .alt = Ymuno â sgwrs
+
+chat-left-chat-icon2 =
+    .alt = Gadael sgwrs
+
+chat-participant-owner-role-icon2 =
+    .alt = Perchennog
+
+chat-participant-administrator-role-icon2 =
+    .alt = Gweinyddwr
+
+chat-participant-moderator-role-icon2 =
+    .alt = Cymedrolwr
+
+chat-participant-voiced-role-icon2 =
+    .alt = Gall gyfranogwr anfon negeseuon
+
+chat-verify-identity =
+    .label = Gwirio Hunaniaeth
+    .accesskey = G
+
+chat-identity-verified =
+    .label = Hunaniaeth wedi'i gwirio eisoes
+
+chat-buddy-identity-status = Ymddiriedaeth Amgryptio
+chat-buddy-identity-status-verified = Gwiriwyd
+chat-buddy-identity-status-unverified = Heb ei wirio
+
+## Conversation invite notification box
+
+# This string appears in a notification bar at the top of the Contacts window
+# when someone invited the user to a multi user chat conversation, to request
+# the user to confirm they want to join the chat.
+# Variables:
+#   $conversation (String) - Name of the conversation the user is invited to.
+chat-conv-invite-label = Rydych wedi'ch gwahodd i sgwrsio yn { $conversation }
+chat-conv-invite-accept =
+    .label = Derbyn
+    .accesskey = D
+chat-conv-invite-deny =
+    .label = Gwrthod
+    .accesskey = G
diff --git a/thunderbird-l10n/cy/localization/cy/messenger/compactFoldersDialog.ftl b/thunderbird-l10n/cy/localization/cy/messenger/compactFoldersDialog.ftl
new file mode 100644
index 0000000000..69366b7d62
--- /dev/null
+++ b/thunderbird-l10n/cy/localization/cy/messenger/compactFoldersDialog.ftl
@@ -0,0 +1,20 @@
+# This Source Code Form is subject to the terms of the Mozilla Public
+# License, v. 2.0. If a copy of the MPL was not distributed with this
+# file, You can obtain one at http://mozilla.org/MPL/2.0/.
+
+compact-dialog-window-title =
+    .title = Cywasgu ffolderi
+compact-folders-dialog-title = Cywasgu ffolderi
+compact-dialog =
+    .buttonlabelaccept = Cywasgu nawr
+    .buttonaccesskeyaccept = C
+    .buttonlabelcancel = Atgoffa fi yn hwyrach
+    .buttonaccesskeycancel = A
+    .buttonlabelextra1 = Dysgu rhagor…
+    .buttonaccesskeyextra1 = D
+# Variables:
+#  $data (String): The amount of space to be freed, formatted byte, MB, GB, etc., based on the size.
+compact-dialog-message = Mae angen i { -brand-short-name } wneud gwaith cynnal a chadw ffeiliau yn rheolaidd i wella perfformiad eich ffolderi e-bost. Bydd hyn yn adfer { $data } o ofod disg heb newid eich negeseuon. I adael i { -brand-short-name } wneud hyn yn awtomatig yn y dyfodol heb ofyn, ticiwch y blwch isod cyn dewis ‘{ compact-dialog.buttonlabelaccept }’.
+compact-dialog-never-ask-checkbox =
+    .label = Cywasgu ffolderi yn awtomatig yn y dyfodol
+    .accesskey = a
diff --git a/thunderbird-l10n/cy/localization/cy/messenger/exportDialog.ftl b/thunderbird-l10n/cy/localization/cy/messenger/exportDialog.ftl
new file mode 100644
index 0000000000..0f8bd587a4
--- /dev/null
+++ b/thunderbird-l10n/cy/localization/cy/messenger/exportDialog.ftl
@@ -0,0 +1,22 @@
+# This Source Code Form is subject to the terms of the Mozilla Public
+# License, v. 2.0. If a copy of the MPL was not distributed with this
+# file, You can obtain one at http://mozilla.org/MPL/2.0/.
+
+export-dialog-brand-name = { -brand-product-name }
+
+export-dialog-title = Allforio
+
+export-dialog =
+    .buttonlabelaccept = Nesaf
+
+export-dialog-button-finish = Gorffen
+
+export-dialog-file-picker = Allforio i ffeil zip
+
+export-dialog-description1 = Allforio cyfrifon e-bost, negeseuon e-bost, llyfrau cyfeiriadau a dewisiadau i ffeil zip.
+
+export-dialog-desc2 = Pan fydd angen, gallwch fewnforio'r ffeil zip i adfer eich proffil.
+
+export-dialog-exporting = Yn allforio…
+
+export-dialog-exported = Wedi'i allforio!
diff --git a/thunderbird-l10n/cy/localization/cy/messenger/extensionPermissions.ftl b/thunderbird-l10n/cy/localization/cy/messenger/extensionPermissions.ftl
new file mode 100644
index 0000000000..00621129dd
--- /dev/null
+++ b/thunderbird-l10n/cy/localization/cy/messenger/extensionPermissions.ftl
@@ -0,0 +1,27 @@
+# This Source Code Form is subject to the terms of the Mozilla Public
+# License, v. 2.0. If a copy of the MPL was not distributed with this
+# file, You can obtain one at http://mozilla.org/MPL/2.0/.
+
+
+## Extension permission description keys are derived from permission names.
+## Permissions for which the message has been changed and the key updated
+## must have a corresponding entry in the `PERMISSION_L10N_ID_OVERRIDES` map.
+
+webext-perms-description-accountsFolders = Creu, ailenwi neu ddileu ffolderi eich cyfrif e-bost
+webext-perms-description-accountsIdentities = Creu, newid neu ddileu ffolderi eich cyfrif e-bost
+webext-perms-description-accountsRead = Gweld eich cyfrifon e-bost, eu hunaniaeth a'u ffolderi
+webext-perms-description-addressBooks = Darllenwch ac addasu eich llyfrau cyfeiriad a chysylltiadau
+webext-perms-description-compose = Darllenwch ac addasu eich negeseuon e-bost wrth i chi eu cyfansoddi a'u hanfon
+webext-perms-description-compose-send = Anfon negeseuon e-bost wedi'u cyfansoddi ar eich rhan
+webext-perms-description-compose-save = Cadw negeseuon e-bost wedi'u hysgrifennu fel drafftiau neu dempledi
+webext-perms-description-experiment = Meddu ar fynediad llawn, heb gyfyngiad i { -brand-short-name }, a'ch cyfrifiadur
+webext-perms-description-messagesImport = Mewnforio negeseuon i Thunderbird
+webext-perms-description-messagesModify = Darllenwch ac addaswch eich negeseuon e-bost wrth iddyn nhw gael eu dangos i chi
+webext-perms-description-messagesMove = Copïo neu symud eich negeseuon e-bost (gan gynnwys eu symud i'r ffolder sbwriel)
+webext-perms-description-messagesDelete = Dileu eich negeseuon e-bost yn barhaol
+webext-perms-description-messagesRead = Darllenwch eich negeseuon e-bost a'u marcio neu eu tagio
+webext-perms-description-messagesRead2 = Darllenwch eich negeseuon e-bost
+webext-perms-description-messagesUpdate = Newidiwch briodweddau a thagiau eich negeseuon e-bost
+webext-perms-description-messagesTags = Creu, addasu a dileu tagiau neges
+webext-perms-description-messagesTagsList = Rhestr y tagiau neges
+webext-perms-description-sensitiveDataUpload = Trosglwyddo data defnyddwyr sensitif (os yw mynediad wedi'i ganiatáu) i weinydd pell i'w brosesu ymhellach
diff --git a/thunderbird-l10n/cy/localization/cy/messenger/extensions/popup.ftl b/thunderbird-l10n/cy/localization/cy/messenger/extensions/popup.ftl
new file mode 100644
index 0000000000..f3992c693f
--- /dev/null
+++ b/thunderbird-l10n/cy/localization/cy/messenger/extensions/popup.ftl
@@ -0,0 +1,14 @@
+# This Source Code Form is subject to the terms of the Mozilla Public
+# License, v. 2.0. If a copy of the MPL was not distributed with this
+# file, You can obtain one at http://mozilla.org/MPL/2.0/.
+
+close-shortcut =
+    .key = f
+# Variables:
+#   $title (String): the title of the popup window
+extension-popup-title =
+    { PLATFORM() ->
+        [macos] { $title }
+       *[other] { $title } - { -brand-full-name }
+    }
+extension-popup-default-title = { -brand-full-name }
diff --git a/thunderbird-l10n/cy/localization/cy/messenger/extensionsUI.ftl b/thunderbird-l10n/cy/localization/cy/messenger/extensionsUI.ftl
new file mode 100644
index 0000000000..9a32dcebae
--- /dev/null
+++ b/thunderbird-l10n/cy/localization/cy/messenger/extensionsUI.ftl
@@ -0,0 +1,9 @@
+# This Source Code Form is subject to the terms of the Mozilla Public
+# License, v. 2.0. If a copy of the MPL was not distributed with this
+# file, You can obtain one at http://mozilla.org/MPL/2.0/.
+
+webext-experiment-warning = Gall ychwanegion maleisus ddwyn eich manylion preifat neu gyfaddawdu eich cyfrifiadur. Gosodwch yr ychwanegiad hwn dim ond os ydych yn ymddiried yn y ffynhonnell.
+webext-perms-learn-more = Dysgu rhagor
+# Variables:
+#   $addonName (String): localized named of the extension that was just installed.
+addon-post-install-message = Ychwanegwyd { $addonName }
diff --git a/thunderbird-l10n/cy/localization/cy/messenger/firefoxAccounts.ftl b/thunderbird-l10n/cy/localization/cy/messenger/firefoxAccounts.ftl
new file mode 100644
index 0000000000..db3776e399
--- /dev/null
+++ b/thunderbird-l10n/cy/localization/cy/messenger/firefoxAccounts.ftl
@@ -0,0 +1,32 @@
+# This Source Code Form is subject to the terms of the Mozilla Public
+# License, v. 2.0. If a copy of the MPL was not distributed with this
+# file, you can obtain one at http://mozilla.org/MPL/2.0/.
+
+# “Account” can be localized, “Firefox” must be treated as a brand,
+# and kept in English.
+-fxaccount-brand-name =
+    { $capitalization ->
+        [sentence] { "Cyfrif Firefox" }
+       *[title] { "Cyfrif Firefox" }
+    }
+
+## These strings are shown in a desktop notification after the user requests we resend a verification email.
+
+fxa-verification-sent-title = Dilysiad wedi'i Anfon
+# Variables:
+# $userEmail (String) - Email address of user's Firefox Account.
+fxa-verification-sent-body = Mae dolen dilysu wedi'i anfon at { $userEmail }.
+fxa-verification-not-sent-title = Methu Anfon Dilysiad
+fxa-verification-not-sent-body = Nid ydym yn gallu anfon e-bost dilysu ar hyn o bryd, ceisiwch eto'n hwyrach.
+
+## These strings are shown in a confirmation dialog when the user chooses to sign out.
+
+fxa-signout-dialog-title = Allgofnodwch o { -fxaccount-brand-name(capitalization: "sentence") }?
+fxa-signout-dialog-body = Bydd data wedi'i gydweddu'n aros yn eich cyfrif.
+fxa-signout-dialog-button = Allgofnodi
+
+## These strings are shown in a confirmation dialog when the user chooses to stop syncing.
+
+sync-disconnect-dialog-title = Datgysylltu?
+sync-disconnect-dialog-body = Bydd { -brand-product-name } yn datgysylltu o'ch cyfrif ond ni fydd yn dileu dim o'ch data pori ar y ddyfais hon.
+sync-disconnect-dialog-button = Datgysylltu
diff --git a/thunderbird-l10n/cy/localization/cy/messenger/flatpak.ftl b/thunderbird-l10n/cy/localization/cy/messenger/flatpak.ftl
new file mode 100644
index 0000000000..6a8df6e396
--- /dev/null
+++ b/thunderbird-l10n/cy/localization/cy/messenger/flatpak.ftl
@@ -0,0 +1,24 @@
+# This Source Code Form is subject to the terms of the Mozilla Public
+# License, v. 2.0. If a copy of the MPL was not distributed with this
+# file, You can obtain one at http://mozilla.org/MPL/2.0/.
+
+
+### These messages are used by the Thunderbird Linux Flatpak "desktop" file.
+### An end user will see them associated with the application launcher icon
+
+# This is the label on the icon
+flatpak-desktop-name = { -brand-short-name }
+# Appears as a tooltip when hovering over application menu entry
+flatpak-desktop-comment = Anfon a derbyn e-bost gyda { -brand-product-name }
+# A generic description of Thunderbird
+flatpak-desktop-generic-name = Rhaglen E-bost
+
+## Actions Section
+## These are alternative ways of starting Thunderbird, such as open the compose
+## window to write a message. Visible in a context menu after right clicking a
+## Thunderbird taskbar icon, possibly other places depending on the environment.
+
+flatpak-desktop-action-compose = Ysgrifennu Neges Newydd
+flatpak-desktop-action-addressbook = Agor y Llyfr Cyfeiriadau
+flatpak-desktop-action-calendar = Agor y Calendr
+flatpak-desktop-action-keymanager = Agor y Rheolwr Allwedd OpenPGP
diff --git a/thunderbird-l10n/cy/localization/cy/messenger/folderprops.ftl b/thunderbird-l10n/cy/localization/cy/messenger/folderprops.ftl
new file mode 100644
index 0000000000..f6d675e472
--- /dev/null
+++ b/thunderbird-l10n/cy/localization/cy/messenger/folderprops.ftl
@@ -0,0 +1,10 @@
+# This Source Code Form is subject to the terms of the Mozilla Public
+# License, v. 2.0. If a copy of the MPL was not distributed with this
+# file, You can obtain one at http://mozilla.org/MPL/2.0/.
+
+
+## Quota tab
+
+# Variables:
+#   $percent (Number) - Usage percentage of the assigned IMAP quota.
+quota-percent-used = { $percent }% yn llawn
diff --git a/thunderbird-l10n/cy/localization/cy/messenger/importDialog.ftl b/thunderbird-l10n/cy/localization/cy/messenger/importDialog.ftl
new file mode 100644
index 0000000000..fe71f6fa23
--- /dev/null
+++ b/thunderbird-l10n/cy/localization/cy/messenger/importDialog.ftl
@@ -0,0 +1,30 @@
+# This Source Code Form is subject to the terms of the Mozilla Public
+# License, v. 2.0. If a copy of the MPL was not distributed with this
+# file, You can obtain one at http://mozilla.org/MPL/2.0/.
+
+# Short name of the import module
+thunderbird-import-name = Thunderbird
+
+# Description of the import module
+thunderbird-import-description = Mewnforio e-bost o gyfeiriadur proffil Thunderbird.
+
+import-from-thunderbird-zip =
+    .label = Thunderbird (copi wrth gefn o broffil wedi'i allforio; ffeil sip llai na 2GB)
+    .accesskey = T
+
+import-from-thunderbird-dir =
+    .label = Thunderbird (ffolder proffil)
+    .accesskey = p
+
+import-select-profile-zip = Dewiswch gyfeiriadur proffil wedi'i zipio
+
+import-select-profile-dir = Dewis cyfeiriadur proffil
+
+zip-file-too-big-title = Mae'r Ffeil Zip yn Rhy Fawr
+
+zip-file-too-big-message = Mae'r ffeil zip a ddewiswyd yn fwy na 2GB. Echdynnwch hi'n gyntaf, yna ei mewnforio o'r ffolder cafodd ei hechdynnu.
+
+wizardpage-failed =
+    .label = Methodd y Mewnforio
+
+wizardpage-failed-message = Methodd y mewnforio yn annisgwyl, efallai y bydd mwy o wybodaeth ar gael yn y Consol Gwallau.
diff --git a/thunderbird-l10n/cy/localization/cy/messenger/mailWidgets.ftl b/thunderbird-l10n/cy/localization/cy/messenger/mailWidgets.ftl
new file mode 100644
index 0000000000..38ed76eb85
--- /dev/null
+++ b/thunderbird-l10n/cy/localization/cy/messenger/mailWidgets.ftl
@@ -0,0 +1,15 @@
+# This Source Code Form is subject to the terms of the Mozilla Public
+# License, v. 2.0. If a copy of the MPL was not distributed with this
+# file, You can obtain one at http://mozilla.org/MPL/2.0/.
+
+apply-current-view-to-menu =
+    .label = Gosod yr olwg gyfredol i…
+
+threadpane-apply-changes-prompt-title = Gosod y Newidiadau?
+# Variables:
+#  $name (String): The name of the folder to apply to.
+threadpane-apply-changes-prompt-no-children-text = Gosod golwg y ffolder gyfredol i { $name }?
+# Variables:
+#  $name (String): The name of the folder to apply to.
+threadpane-apply-changes-prompt-with-children-text = Gosod golwg y ffolder gyfredol i { $name } a'i phlant?
+
diff --git a/thunderbird-l10n/cy/localization/cy/messenger/menubar.ftl b/thunderbird-l10n/cy/localization/cy/messenger/menubar.ftl
new file mode 100644
index 0000000000..505d4a89a3
--- /dev/null
+++ b/thunderbird-l10n/cy/localization/cy/messenger/menubar.ftl
@@ -0,0 +1,144 @@
+# This Source Code Form is subject to the terms of the Mozilla Public
+# License, v. 2.0. If a copy of the MPL was not distributed with this
+# file, You can obtain one at http://mozilla.org/MPL/2.0/.
+
+toolbar-context-menu-menu-bar =
+    .toolbarname = Bar Dewislen
+    .accesskey = D
+
+## Tools Menu
+
+menu-tools-settings =
+    .label = Gosodiadau
+    .accesskey = G
+menu-addons-and-themes =
+    .label = Ychwanegion a Themâu
+    .accesskey = Y
+
+## Help Menu
+
+menu-help-help-title =
+    .label = Cymorth
+    .accesskey = C
+menu-help-get-help =
+    .label = Derbyn Cymorth
+    .accesskey = D
+menu-help-explore-features =
+    .label = Edrych ar y Nodweddion
+    .accesskey = E
+menu-help-shortcuts =
+    .label = Llwybrau Byr Bysellfwrdd
+    .accesskey = L
+menu-help-get-involved =
+    .label = Ymunwch
+    .accesskey = Y
+menu-help-donation =
+    .label = Gwnewch Rodd
+    .accesskey = G
+menu-help-share-feedback =
+    .label = Rhannwch Syniadau ac Adborth…
+    .accesskey = R
+menu-help-enter-troubleshoot-mode =
+    .label = Y Modd Datrys Problemau…
+    .accesskey = M
+menu-help-exit-troubleshoot-mode =
+    .label = Diffodd y Modd Datrys Problemau
+    .accesskey = D
+menu-help-more-troubleshooting-info =
+    .label = Rhagor o Wybodaeth Datrys Problemau
+    .accesskey = R
+menu-help-troubleshooting-info =
+    .label = Gwybodaeth am Ddatrys Problemau
+    .accesskey = G
+menu-help-about-product =
+    .label = Ynghylch { -brand-short-name }
+    .accesskey = Y
+# These menu-quit strings are only used on Windows and Linux.
+menu-quit =
+    .label =
+        { PLATFORM() ->
+            [windows] Gorffen
+           *[other] Gadael
+        }
+    .accesskey =
+        { PLATFORM() ->
+            [windows] G
+           *[other] a
+        }
+# This menu-quit-mac string is only used on macOS.
+menu-quit-mac =
+    .label = Gadael { -brand-shorter-name }
+quit-app-shortcut =
+    .key = G
+
+## Mail Toolbar
+
+toolbar-junk-button =
+    .label = Sbam
+    .tooltiptext = Marcio'r negeseuon hyn fel sbam
+toolbar-not-junk-button =
+    .label = Nid Sbam
+    .tooltiptext = Marcio'r negeseuon hyn fel nid sbam
+toolbar-delete-button =
+    .label = Dileu
+    .tooltiptext = Dileu'r negeseuon neu ffolderi hyn
+toolbar-undelete-button =
+    .label = Dad-ddileu
+    .tooltiptext = Dad-ddileu'r negeseuon hyn
+
+## View
+
+menu-view-repair-text-encoding =
+    .label = Trwsio Amgodio Testun
+    .accesskey = T
+
+## View / Folders
+
+menu-view-folders-toggle-header =
+    .label = Penyn Paen Ffolder
+    .accesskey = P
+
+## View / Layout
+
+menu-view-toggle-thread-pane-header =
+    .label = Pennyn Rhestrau Negeseuon
+    .accesskey = P
+menu-font-size-label =
+    .label = Maint Ffont
+    .accesskey = M
+menuitem-font-size-enlarge =
+    .label = Cynyddu Maint Ffont
+    .accesskey = F
+menuitem-font-size-reduce =
+    .label = Lleihau Maint Ffont
+    .accesskey = L
+menuitem-font-size-reset =
+    .label = Ailosod Maint Ffont
+    .accesskey = A
+mail-uidensity-label =
+    .label = Dwysedd
+    .accesskey = D
+mail-uidensity-compact =
+    .label = Cywasgu
+    .accesskey = C
+mail-uidensity-normal =
+    .label = Arferol
+    .accesskey = A
+mail-uidensity-touch =
+    .label = Cyffwrdd
+    .accesskey = y
+mail-uidensity-default =
+    .label = Rhagosodiad
+    .accesskey = R
+mail-uidensity-relaxed =
+    .label = Llaes
+    .accesskey = L
+menu-spaces-toolbar-button =
+    .label = Bar Offer Mannau
+    .accesskey = B
+
+## File
+
+file-new-newsgroup-account =
+    .label = Cyfrif Grŵp Newyddion…
+    .accesskey = N
diff --git a/thunderbird-l10n/cy/localization/cy/messenger/messageheader/headerFields.ftl b/thunderbird-l10n/cy/localization/cy/messenger/messageheader/headerFields.ftl
new file mode 100644
index 0000000000..cf6d56e55e
--- /dev/null
+++ b/thunderbird-l10n/cy/localization/cy/messenger/messageheader/headerFields.ftl
@@ -0,0 +1,49 @@
+# This Source Code Form is subject to the terms of the Mozilla Public
+# License, v. 2.0. If a copy of the MPL was not distributed with this
+# file, You can obtain one at http://mozilla.org/MPL/2.0/.
+
+
+## Header lists
+
+message-header-to-list-name = At
+message-header-from-list-name = Oddi wrth
+message-header-sender-list-name = Anfonwr
+message-header-reply-to-list-name = Ateb i
+message-header-cc-list-name = Cc
+message-header-bcc-list-name = Bcc
+message-header-newsgroups-list-name = Grwpiau Newyddion
+message-header-followup-to-list-name = Ymateb i
+message-header-tags-list-name = Tagiau
+
+## Other message headers.
+## The field-separator is for screen readers to separate the field name from the field value.
+
+message-header-author-field = Awdur<span data-l10n-name="field-separator">:</span>
+message-header-organization-field = Corff<span data-l10n-name="field-separator">:</span>
+message-header-subject-field = Pwnc<span data-l10n-name="field-separator">:</span>
+message-header-followup-to-field = Dilynol i<span data-l10n-name="field-separator">:</span>
+message-header-date-field = Dyddiad<span data-l10n-name="field-separator">:</span>
+message-header-user-agent-field = Asiant defnyddiwr<span data-l10n-name="field-separator">:</span>
+message-header-references-field = Cyfeiriadau<span data-l10n-name="field-separator">:</span>
+message-header-message-id-field = ID Neges<span data-l10n-name="field-separator">:</span>
+message-header-in-reply-to-field = Wrth ateb i<span data-l10n-name="field-separator">:</span>
+message-header-website-field = Gwefan<span data-l10n-name="field-separator">:</span>
+# An additional email header field that the user has chosen to display. Unlike
+# the other headers, the name of this header is not expected to be localised
+# because it is generated from the raw field name found in the email header.
+#   $fieldName (String) - The field name.
+message-header-custom-field = { $fieldName }<span data-l10n-name="field-separator">:</span>
+
+##
+
+message-header-address-in-address-book-icon2 =
+    .alt = Yn y Llyfr Cyfeiriadau
+message-header-address-not-in-address-book-icon2 =
+    .alt = Ddim yn y Llyfr Cyfeiriadau
+message-header-address-not-in-address-book-button =
+    .title = Cadw'r cyfeiriad hwn i'r Llyfr Cyfeiriadau
+message-header-address-in-address-book-button =
+    .title = Golygu cysylltiad
+message-header-field-show-more = Rhagor
+    .title = Dangos pob derbynnydd
+message-ids-field-show-all = Dangos y cyfan
diff --git a/thunderbird-l10n/cy/localization/cy/messenger/messenger.ftl b/thunderbird-l10n/cy/localization/cy/messenger/messenger.ftl
new file mode 100644
index 0000000000..28294248e9
--- /dev/null
+++ b/thunderbird-l10n/cy/localization/cy/messenger/messenger.ftl
@@ -0,0 +1,439 @@
+# This Source Code Form is subject to the terms of the Mozilla Public
+# License, v. 2.0. If a copy of the MPL was not distributed with this
+# file, You can obtain one at http://mozilla.org/MPL/2.0/.
+
+
+## Window controls
+
+messenger-window-minimize-button =
+    .tooltiptext = Lleihau
+messenger-window-maximize-button =
+    .tooltiptext = Mwyhau
+messenger-window-restore-down-button =
+    .tooltiptext = Adfer i Lawr
+messenger-window-close-button =
+    .tooltiptext = Cau
+# Variables:
+# $count (Number) - Number of unread messages.
+unread-messages-os-tooltip =
+    { $count ->
+        [zero] 0 negeseuon heb eu darllen
+        [one] 1 neges heb ei darllen
+        [two] { $count } neges heb eu darllen
+        [few] { $count } neges heb eu darllen
+        [many] { $count } neges heb eu darllen
+       *[other] { $count } neges heb eu darllen
+    }
+about-rights-notification-text = Mae { -brand-short-name } yn feddalwedd cod agored am ddim, wedi'i adeiladu gan gymuned o filoedd o bob cwr o'r byd.
+
+## Content tabs
+
+content-tab-page-loading-icon =
+    .alt = Mae'r dudalen yn llwytho
+content-tab-security-high-icon =
+    .alt = Mae'r cysylltiad yn ddiogel
+content-tab-security-broken-icon =
+    .alt = Nid yw'r cysylltiad yn ddiogel
+
+# Back
+
+# Variables
+#   $shortcut (String) - A keyboard shortcut for the Go Back command.
+content-tab-menu-back =
+    .tooltiptext = Nôl un tudalen ({ $shortcut })
+    .aria-label = Nôl
+    .accesskey = N
+# This menuitem is only visible on macOS
+content-tab-menu-back-mac =
+    .label = Nôl
+    .accesskey = ô
+
+# Forward
+
+# Variables
+#   $shortcut (String) - A keyboard shortcut for the Go Forward command.
+content-tab-menu-forward =
+    .tooltiptext = Ymlaen un tudalen ({ $shortcut })
+    .aria-label = Ymlaen
+    .accesskey = Y
+# This menuitem is only visible on macOS
+content-tab-menu-forward-mac =
+    .label = Ymlaen
+    .accesskey = m
+
+# Reload
+
+content-tab-menu-reload =
+    .tooltiptext = Ail lwytho tudalen
+    .aria-label = Ail lwytho
+    .accesskey = A
+# This menuitem is only visible on macOS
+content-tab-menu-reload-mac =
+    .tooltiptext = Ail lwytho tudalen
+    .label = Ail lwytho
+    .accesskey = i
+
+# Stop
+
+content-tab-menu-stop =
+    .tooltiptext = Atal llwytho tudalen
+    .aria-label = Atal
+    .accesskey = t
+# This menuitem is only visible on macOS
+content-tab-menu-stop-mac =
+    .tooltiptext = Atal llwytho tudalen
+    .label = Atal
+    .accesskey = l
+
+## Toolbar
+
+addons-and-themes-toolbarbutton =
+    .label = Ychwanegion a Themâu
+    .tooltiptext = Rheoli eich ychwanegion
+quick-filter-toolbarbutton =
+    .label = Hidl Cyflym
+    .tooltiptext = Hidlo negeseuon
+redirect-msg-button =
+    .label = Ailgyfeirio
+    .tooltiptext = Ailgyfeirio'r neges hon
+
+## Folder Pane
+
+folder-pane-toolbar =
+    .toolbarname = Bar Offer Paen Ffolder
+    .accesskey = P
+folder-pane-toolbar-options-button =
+    .tooltiptext = Opsiynau Ffolder Paen
+folder-pane-header-label = Ffolderi
+
+## Folder Toolbar Header Popup
+
+folder-toolbar-hide-toolbar-toolbarbutton =
+    .label = Cuddio'r Bar Offer
+    .accesskey = C
+show-all-folders-label =
+    .label = Pob Ffolder
+    .accesskey = P
+show-unread-folders-label =
+    .label = Ffolderi Heb eu Darllen
+    .accesskey = H
+show-favorite-folders-label =
+    .label = Hoff Ffolderi
+    .accesskey = H
+show-smart-folders-label =
+    .label = Ffolderi a Unwyd
+    .accesskey = U
+show-recent-folders-label =
+    .label = Ffolderi Diweddar
+    .accesskey = D
+show-tags-folders-label =
+    .label = Tagiau
+    .accesskey = T
+folder-toolbar-toggle-folder-compact-view =
+    .label = Golwg Cryno
+    .accesskey = G
+
+## File Menu
+
+menu-file-save-as-file =
+    .label = Ffeil…
+    .accesskey = F
+
+## Edit Menu
+
+menu-edit-delete-folder =
+    .label = Dileu Ffolder
+    .accesskey = F
+menu-edit-unsubscribe-newsgroup =
+    .label = Dad-danysgrifio Grŵp Newyddion
+    .accesskey = D
+# Variables:
+# $count (Number) - Number of selected messages.
+menu-edit-delete-messages =
+    .label =
+        { $count ->
+            [zero] Dim Negeseuon i'w Dileu
+            [one] Dileu Neges
+            [two] Dileu'r Negeseuon Hyn
+            [few] Dileu'r Negeseuon Hyn
+            [many] Dileu'r Negeseuon Hyn
+           *[other] Dileu'r Negeseuon Hyn
+        }
+    .accesskey = N
+# Variables:
+# $count (Number) - Number of selected messages.
+menu-edit-undelete-messages =
+    .label =
+        { $count ->
+            [zero] Does Dim Negeseuon i'w Dileu
+            [one] Dad-ddileu Neges
+            [two] Dad-ddileu'r Negeseuon Hyn
+            [few] Dad-ddileu'r Negeseuon Hyn
+            [many] Dad-ddileu'r Negeseuon Hyn
+           *[other] Dad-ddileu'r Negeseuon Hyn
+        }
+    .accesskey = a
+menu-edit-properties =
+    .label = Priodweddau
+    .accesskey = P
+menu-edit-folder-properties =
+    .label = Priodweddau Ffolderi
+    .accesskey = F
+menu-edit-newsgroup-properties =
+    .label = Priodweddau Grŵp Newyddion
+    .accesskey = G
+
+## Message Menu
+
+redirect-msg-menuitem =
+    .label = Ailgyfeirio
+    .accesskey = A
+
+## AppMenu
+
+appmenu-save-as-file =
+    .label = Ffeil…
+appmenu-settings =
+    .label = Gosodiadau
+appmenu-addons-and-themes =
+    .label = Ychwanegion a Themâu
+
+## Context menu
+
+context-menu-redirect-msg =
+    .label = Ailgyfeirio
+# This menu item is for canceling an NNTP message
+context-menu-cancel-msg =
+    .label = Diddymu Neges
+# Variables:
+# $count (Number) - Number of selected messages.
+mail-context-delete-messages =
+    .label =
+        { $count ->
+            [zero] Dileu'r Negeseuon Hyn
+            [one] Dileu'r Neges Hon
+            [two] Dileu'r Negeseuon Hyn
+            [few] Dileu'r Negeseuon Hyn
+            [many] Dileu'r Negeseuon Hyn
+           *[other] Dileu'r Negeseuon Hyn
+        }
+# Variables:
+# $count (Number) - Number of selected messages.
+mail-context-undelete-messages =
+    .label =
+        { $count ->
+            [zero] Does Dim Negeseuon i'w Dileu
+            [one] Dad-ddileu Neges
+            [two] Dad-ddileu'r Negeseuon Hyn
+            [few] Dad-ddileu'r Negeseuon Hyn
+            [many] Dad-ddileu'r Negeseuon Hyn
+           *[other] Dad-ddileu'r Negeseuon Hyn
+        }
+context-menu-decrypt-to-folder2 =
+    .label = Creu Copi Wedi'i Ddadgryptio Yn
+    .accesskey = D
+
+## Message header pane
+
+other-action-redirect-msg =
+    .label = Ailgyfeirio
+message-header-msg-flagged =
+    .title = Serennog
+    .aria-label = Serennog
+# Variables:
+# $address (String) - The email address of the recipient this picture belongs to.
+message-header-recipient-avatar =
+    .alt = Llun proffil { $address }.
+
+## Message header cutomize panel
+
+message-header-customize-panel-title = Gosodiadau Pennyn Neges
+message-header-customize-button-style =
+    .value = Arddull botwm
+    .accesskey = B
+message-header-button-style-default =
+    .label = Eiconau a thestun
+message-header-button-style-text =
+    .label = Testun
+message-header-button-style-icons =
+    .label = Eiconau
+message-header-show-sender-full-address =
+    .label = Dangos cyfeiriad llawn yr anfonwr bob tro
+    .accesskey = l
+message-header-show-sender-full-address-description = Bydd y cyfeiriad e-bost yn cael ei ddangos o dan yr enw dangos.
+message-header-show-recipient-avatar =
+    .label = Dangos llun proffil yr anfonwr
+    .accesskey = D
+message-header-show-big-avatar =
+    .label = Llun proffil mwy
+    .accesskey = L
+message-header-hide-label-column =
+    .label = Cuddio colofn y labeli
+    .accesskey = u
+message-header-large-subject =
+    .label = Pwnc mawr
+    .accesskey = P
+message-header-all-headers =
+    .label = Dangos pob pennyn
+    .accesskey = D
+
+## Action Button Context Menu
+
+toolbar-context-menu-manage-extension =
+    .label = Rheoli Estyniad
+    .accesskey = E
+toolbar-context-menu-remove-extension =
+    .label = Tynnu Estyniad
+    .accesskey = T
+
+## Add-on removal warning
+
+# Variables:
+#  $name (String): The name of the add-on that will be removed.
+addon-removal-title = Tynnu { $name }?
+addon-removal-confirmation-button = Tynnu
+# Variables:
+#  $name (String): The name of the add-on that will be removed.
+addon-removal-confirmation-message = Tynnu { $name } yn ogystal â'i ffurfweddiad a'i ddata o { -brand-short-name }?
+caret-browsing-prompt-title = Pori Caret
+caret-browsing-prompt-text = Mae pwyso F7 yn cychwyn a diffodd Pori Caret. Mae'r nodwedd hon yn gosod cyrchwr symudol ar dudalennau gwe, gan ganiatáu i chi ddewis testun gyda'r bysellfwrdd. Hoffech chi gychwyn Pori Caret?
+caret-browsing-prompt-check-text = Peidio â gofyn eto.
+repair-text-encoding-button =
+    .label = Trwsio Amgodio Testun
+    .tooltiptext = Dyfalu'r amgodiad testun cywir o gynnwys y neges
+
+## no-reply handling
+
+no-reply-title = Nid yw Ateb yn cael ei Gefnogi
+# Variables:
+# $email (String) - Email address the reply will be sent to. Example: "noreply@example.com"
+no-reply-message = Nid yw'n ymddangos bod y cyfeiriad ateb ({ $email }) yn gyfeiriad wedi'i fonitro. Mae'n bosib na fydd unrhyw un yn darllen negeseuon i'r cyfeiriad hwn.
+no-reply-reply-anyway-button = Ateb Beth Bynnag
+
+## error messages
+
+# Variables:
+# $failures (Number) - Number of messages that could not be decrypted.
+# $total (Number) - Total number of messages that were attempted to be decrypted.
+decrypt-and-copy-failures-multiple =
+    { $failures ->
+        [zero] Nid oedd modd dadgryptio { $failures } o { $total } o negeseuon ac nid ydynt wedi'u copïo.
+        [one] Nid oedd modd dadgryptio { $failures } o { $total } o negeseuon ac nid ydynt wedi'u copïo.
+        [two] Nid oedd modd dadgryptio { $failures } o { $total } o negeseuon ac nid ydynt wedi'u copïo.
+        [few] Nid oedd modd dadgryptio { $failures } o { $total } o negeseuon ac nid ydynt wedi'u copïo.
+        [many] Nid oedd modd dadgryptio { $failures } o { $total } o negeseuon ac nid ydynt wedi'u copïo.
+       *[other] Nid oedd modd dadgryptio { $failures } o { $total } o negeseuon ac nid ydynt wedi'u copïo.
+    }
+
+## Spaces toolbar
+
+spaces-toolbar-element =
+    .toolbarname = Bar Offer Mannau
+    .aria-label = Bar Offer Mannau
+    .aria-description = Bar offer fertigol ar gyfer symud rhwng mannau gwahanol. Defnyddiwch y bysellau saeth i ddefnyddio'r botymau sydd ar gael.
+spaces-toolbar-button-mail2 =
+    .title = E-bost
+spaces-toolbar-button-address-book2 =
+    .title = Llyfr Cyfeiriadau
+spaces-toolbar-button-calendar2 =
+    .title = Calendr
+spaces-toolbar-button-tasks2 =
+    .title = Tasgau
+spaces-toolbar-button-chat2 =
+    .title = Sgwrsio
+spaces-toolbar-button-overflow =
+    .title = Rhagor o fannau…
+spaces-toolbar-button-settings2 =
+    .title = Gosodiadau
+spaces-toolbar-button-hide =
+    .title = Cuddio Bar Offer Mannau
+spaces-toolbar-button-show =
+    .title = Dangos Bar Offer Mannau
+spaces-context-new-tab-item =
+    .label = Agor mewn tab newydd
+spaces-context-new-window-item =
+    .label = Agor mewn ffenestr newydd
+# Variables:
+# $tabName (String) - The name of the tab this item will switch to.
+spaces-context-switch-tab-item =
+    .label = Newid i { $tabName }
+settings-context-open-settings-item2 =
+    .label = Gosodiadau
+settings-context-open-account-settings-item2 =
+    .label = Gosodiadau Cyfrif
+settings-context-open-addons-item2 =
+    .label = Ychwanegion a Themâu
+
+## Spaces toolbar pinned tab menupopup
+
+spaces-toolbar-pinned-tab-button =
+    .tooltiptext = Dewislen Mannau
+spaces-pinned-button-menuitem-mail2 =
+    .label = { spaces-toolbar-button-mail2.title }
+spaces-pinned-button-menuitem-address-book2 =
+    .label = { spaces-toolbar-button-address-book2.title }
+spaces-pinned-button-menuitem-calendar2 =
+    .label = { spaces-toolbar-button-calendar2.title }
+spaces-pinned-button-menuitem-tasks2 =
+    .label = { spaces-toolbar-button-tasks2.title }
+spaces-pinned-button-menuitem-chat2 =
+    .label = { spaces-toolbar-button-chat2.title }
+spaces-pinned-button-menuitem-settings2 =
+    .label = { spaces-toolbar-button-settings2.title }
+spaces-pinned-button-menuitem-show =
+    .label = { spaces-toolbar-button-show.title }
+# Variables:
+# $count (Number) - Number of unread messages.
+chat-button-unread-messages = { $count }
+    .title =
+        { $count ->
+            [zero] Dim negeseuon heb eu darllen
+            [one] Un neges neb ei darllen
+            [two] { $count } heb eu darllen
+            [few] { $count } heb eu darllen
+            [many] { $count } heb eu darllen
+           *[other] { $count } heb eu darllen
+        }
+
+## Spaces toolbar customize panel
+
+menuitem-customize-label =
+    .label = Cyfaddasu…
+spaces-customize-panel-title = Gosodiadau Bar Offer Mannau
+spaces-customize-background-color = Lliw cefndir
+spaces-customize-icon-color = Lliw botwm
+# The background color used on the buttons of the spaces toolbar when they are
+# `current`, meaning the related space/tab is active and visible.
+spaces-customize-accent-background-color = Lliw cefndir botwm a ddewiswyd
+# The icon color used on the buttons of the spaces toolbar when they are
+# `current`, meaning the related space/tab is active and visible.
+spaces-customize-accent-text-color = Lliw botwm a ddewiswyd
+spaces-customize-button-restore = Adfer y Rhagosodiadau
+    .accesskey = R
+customize-panel-button-save = Gorffen
+    .accesskey = G
+
+## Quick Filter Bar
+
+# The label to display for the "View... Toolbars..." menu item that controls
+# whether the quick filter bar is visible.
+quick-filter-bar-toggle =
+    .label = Bar Hidlo Cyflym
+    .accesskey = H
+# This is the key used to show the quick filter bar.
+# This should match quick-filter-bar-textbox-shortcut in about3Pane.ftl.
+quick-filter-bar-show =
+    .key = k
+
+## OpenPGP
+
+openpgp-forget = Anghofio cyfrinymadrodd OpenPGP
+
+## Quota panel.
+
+# Variables:
+#   $percent (Number) - Usage percentage of the assigned IMAP quota.
+#   $usage (String) - Current quota usage (may include unit)
+#   $limit (String) - Current quota limit (may include unit)
+quota-panel-percent-used = { $percent }% yn llawn
+    .title = Cwota IMAP: { $usage } wedi'i ddefnyddio o gyfanswm o { $limit }
diff --git a/thunderbird-l10n/cy/localization/cy/messenger/messengercompose/messengercompose.ftl b/thunderbird-l10n/cy/localization/cy/messenger/messengercompose/messengercompose.ftl
new file mode 100644
index 0000000000..05666d3ec7
--- /dev/null
+++ b/thunderbird-l10n/cy/localization/cy/messenger/messengercompose/messengercompose.ftl
@@ -0,0 +1,468 @@
+# This Source Code Form is subject to the terms of the Mozilla Public
+# License, v. 2.0. If a copy of the MPL was not distributed with this
+# file, You can obtain one at http://mozilla.org/MPL/2.0/.
+
+
+## Send Format
+
+compose-send-format-menu =
+    .label = Fformat Anfon
+    .accesskey = F
+compose-send-auto-menu-item =
+    .label = Awtomatig
+    .accesskey = A
+compose-send-both-menu-item =
+    .label = HTML a Thestun Plaen
+    .accesskey = H
+compose-send-html-menu-item =
+    .label = Dim ond HTML
+    .accesskey = D
+compose-send-plain-menu-item =
+    .label = Dim ond Testun Plaen
+    .accesskey = T
+
+## Addressing widget
+
+#   $type (String) - the type of the addressing row
+remove-address-row-button =
+    .title = Tynnu'r maes { $type }
+#   $type (String) - the type of the addressing row
+#   $count (Number) - the number of address pills currently present in the addressing row
+address-input-type-aria-label =
+    { $count ->
+        [0] { $type }
+        [zero] { $type } gydag un cyfeiriad, defnyddiwch fysell y saeth chwith i ganolbwyntio arno.
+        [one] { $type } gyda { $count } cyfeiriad, defnyddiwch fysell y saeth chwith i ganolbwyntio arnyn nhw.
+        [two] { $type } gyda { $count } cyfeiriad, defnyddiwch fysell y saeth chwith i ganolbwyntio arnyn nhw.
+        [few] { $type } gyda { $count } cyfeiriad, defnyddiwch fysell y saeth chwith i ganolbwyntio arnyn nhw.
+        [many] { $type } gyda { $count } cyfeiriad, defnyddiwch fysell y saeth chwith i ganolbwyntio arnyn nhw.
+       *[other] { $type } gyda { $count } cyfeiriad, defnyddiwch fysell y saeth chwith i ganolbwyntio arnyn nhw.
+    }
+#   $email (String) - the email address
+#   $count (Number) - the number of address pills currently present in the addressing row
+pill-aria-label =
+    { $count ->
+        [zero] { $email }, 1 o { $count }: pwyswch Enter i olygu, Delete i ddileu
+        [one] { $email }: pwyswch Enter i olygu, Delete i ddileu
+        [two] { $email }, 1 o { $count }: pwyswch Enter i olygu, Delete i ddileu
+        [few] { $email }, 1 o { $count }: pwyswch Enter i olygu, Delete i ddileu
+        [many] { $email }, 1 o { $count }: pwyswch Enter i olygu, Delete i ddileu
+       *[other] { $email }, 1 o { $count }: pwyswch Enter i olygu, Delete i ddileu
+    }
+#   $email (String) - the email address
+pill-tooltip-invalid-address = Nid yw { $email } yn gyfeiriad e-bost dilys
+#   $email (String) - the email address
+pill-tooltip-not-in-address-book = Nid yw { $email } yn eich llyfr cyfeiriadau
+pill-action-edit =
+    .label = Golygu Cyfeiriad
+    .accesskey = G
+#   $type (String) - the type of the addressing row, e.g. Cc, Bcc, etc.
+pill-action-select-all-sibling-pills =
+    .label = Dewis Pob Cyfeiriad yn { $type }
+    .accesskey = D
+pill-action-select-all-pills =
+    .label = Dewis Pob Cyfeiriad
+    .accesskey = D
+pill-action-move-to =
+    .label = Symud i
+    .accesskey = S
+pill-action-move-cc =
+    .label = Symud i CC
+    .accesskey = C
+pill-action-move-bcc =
+    .label = Symud i Bcc
+    .accesskey = B
+pill-action-expand-list =
+    .label = Ehangu'r Rhestr
+    .accesskey = E
+
+## Attachment widget
+
+ctrl-cmd-shift-pretty-prefix =
+    { PLATFORM() ->
+        [macos] ⇧ ⌘{ " " }
+       *[other] Ctrl+Shift+
+    }
+trigger-attachment-picker-key = A
+toggle-attachment-pane-key = P
+menuitem-toggle-attachment-pane =
+    .label = Paen Atodiad
+    .accesskey = P
+    .acceltext = { ctrl-cmd-shift-pretty-prefix }{ toggle-attachment-pane-key }
+toolbar-button-add-attachment =
+    .label = Atodi
+    .tooltiptext = Atodi Atodiad ({ ctrl-cmd-shift-pretty-prefix }{ trigger-attachment-picker-key })
+add-attachment-notification-reminder2 =
+    .label = Ychwanegu Atodiad…
+    .accesskey = A
+    .tooltiptext = { toolbar-button-add-attachment.tooltiptext }
+menuitem-attach-files =
+    .label = Ffeil(iau)…
+    .accesskey = F
+    .acceltext = { ctrl-cmd-shift-pretty-prefix }{ trigger-attachment-picker-key }
+context-menuitem-attach-files =
+    .label = Atodi Ffeil(iau)…
+    .accesskey = F
+    .acceltext = { ctrl-cmd-shift-pretty-prefix }{ trigger-attachment-picker-key }
+# Note: Do not translate the term 'vCard'.
+context-menuitem-attach-vcard =
+    .label = Fy vCard
+    .accesskey = v
+context-menuitem-attach-openpgp-key =
+    .label = Fy Allwedd Gyhoeddus OpenPGP
+    .accesskey = O
+#   $count (Number) - the number of attachments in the attachment bucket
+attachment-bucket-count-value =
+    { $count ->
+        [1] { $count } Atodiad
+        [zero] { $count } Atodiadau
+        [one] { $count } Atodiad
+        [two] { $count } Atodiad
+        [few] { $count } Atodiad
+        [many] { $count } Atodiad
+       *[other] { $count } Atodiad
+    }
+attachment-area-show =
+    .title = Dangos y paen atodi ({ ctrl-cmd-shift-pretty-prefix }{ toggle-attachment-pane-key })
+attachment-area-hide =
+    .title = Cuddio'r paen atodi ({ ctrl-cmd-shift-pretty-prefix }{ toggle-attachment-pane-key })
+
+## Variables:
+## $count (Number) - Number of files being dropped onto the composer.
+
+drop-file-label-attachment =
+    { $count ->
+        [zero] Ychwanegu fel Atodiadau
+        [one] Ychwanegu fel Atodiad
+        [two] Ychwanegu fel Atodiad
+        [few] Ychwanegu fel Atodiad
+        [many] Ychwanegu fel Atodiad
+       *[other] Ychwanegu fel Atodiad
+    }
+drop-file-label-inline =
+    { $count ->
+        [zero] Atodiadau ar-lein
+        [one] Atodiad ar-lein
+        [two] Atodiad ar-lein
+        [few] Atodiad ar-lein
+        [many] Atodiad ar-lein
+       *[other] Atodiad ar-lein
+    }
+
+## Reorder Attachment Panel
+
+move-attachment-first-panel-button =
+    .label = Symud yn Gyntaf
+move-attachment-left-panel-button =
+    .label = Symud i'r Chwith
+move-attachment-right-panel-button =
+    .label = Symud i'r Dde
+move-attachment-last-panel-button =
+    .label = Symud Olaf
+button-return-receipt =
+    .label = Derbynneb
+    .tooltiptext = Gofyn am dderbynneb dychwelyd i'r neges hon
+
+## Encryption
+
+encryption-menu =
+    .label = Diogelwch
+    .accesskey = D
+encryption-toggle =
+    .label = Amgryptio
+    .tooltiptext = Defnyddio amgryptiad ben-i-ben ar gyfer y neges yma
+encryption-options-openpgp =
+    .label = OpenPGP
+    .tooltiptext = Gweld neu newid gosodiadau amgryptio OpenPGP
+encryption-options-smime =
+    .label = S/MIME
+    .tooltiptext = Gweld neu newid goodiadau amgryptio S/MIME
+signing-toggle =
+    .label = Llofnodi
+    .tooltiptext = Defnyddio llofnodi digidol ar gyfer y neges hon
+menu-openpgp =
+    .label = OpenPGP
+    .accesskey = O
+menu-smime =
+    .label = S/MIME
+    .accesskey = S
+menu-encrypt =
+    .label = Amgryptio
+    .accesskey = A
+menu-encrypt-subject =
+    .label = Amgryptio Pwnc
+    .accesskey = p
+menu-sign =
+    .label = Llofnodi Digidol
+    .accesskey = L
+menu-manage-keys =
+    .label = Cynorthwy-ydd Allwedd
+    .accesskey = C
+menu-view-certificates =
+    .label = Gweld Tystysgrifau Derbynwyr
+    .accesskey = G
+menu-open-key-manager =
+    .label = Rheolwr Allwedd
+    .accesskey = R
+openpgp-key-issue-notification-one = Mae amgryptio pen-i-ben yn gofyn am ddatrys materion allweddi ar gyfer { $addr }
+openpgp-key-issue-notification-many = Mae amgryptio pen-i-ben yn gofyn am ddatrys materion allweddi ar gyfer { $count } derbynnydd.
+smime-cert-issue-notification-one = Mae amgryptio pen-i-ben yn gofyn am ddatrys materion tystysgrifau ar gyfer { $addr }.
+smime-cert-issue-notification-many = Mae amgryptio pen-i-ben yn gofyn am ddatrys materion tystysgrifau ar gyfer { $count } derbynnydd.
+# Variables:
+# $addr (String) - Email address (which related to the currently selected
+#                  from address) which isn't set up to end-to-end encryption.
+openpgp-key-issue-notification-from = Nid ydych wedi'ch gosod i anfon negeseuon wedi'u hamgryptio ben-i-ben oddi wrth { $addr }.
+# Variables:
+# $addr (String) - Email address with key issues.
+openpgp-key-issue-notification-single = Mae amgryptio o ben-i-ben yn gofyn am ddatrys problemau allweddol ar gyfer { $addr }.
+# Variables:
+# $count (Number) - Number of recipients with key issues.
+openpgp-key-issue-notification-multi =
+    { $count ->
+        [zero] Mae amgryptio pen-i-ben yn gofyn am ddatrys materion allweddi ar gyfer { $count } derbynnyddion.
+        [one] Mae amgryptio pen-i-ben yn gofyn am ddatrys materion allweddi ar gyfer { $count } derbynnydd.
+        [two] Mae amgryptio pen-i-ben yn gofyn am ddatrys materion allweddi ar gyfer { $count } dderbynnydd.
+        [few] Mae amgryptio pen-i-ben yn gofyn am ddatrys materion allweddi ar gyfer { $count } derbynnydd.
+        [many] Mae amgryptio pen-i-ben yn gofyn am ddatrys materion allweddi ar gyfer { $count } derbynnydd.
+       *[other] Mae amgryptio pen-i-ben yn gofyn am ddatrys materion allweddi ar gyfer { $count } derbynnydd.
+    }
+# Variables:
+# $addr (String) - mail address with certificate issues.
+smime-cert-issue-notification-single = Mae amgryptio pen-i-ben yn gofyn am ddatrys materion tystysgrifau ar gyfer { $addr }.
+# Variables:
+# $count (Number) - Number of recipients with certificate issues.
+smime-cert-issue-notification-multi =
+    { $count ->
+        [zero] Mae amgryptio pen-i-ben yn gofyn am ddatrys materion tystysgrifau ar gyfer { $count } derbynnyddion.
+        [one] Mae amgryptio pen-i-ben yn gofyn am ddatrys materion tystysgrifau ar gyfer { $count } derbynnydd.
+        [two] Mae amgryptio pen-i-ben yn gofyn am ddatrys materion tystysgrifau ar gyfer { $count } dderbynnydd.
+        [few] Mae amgryptio pen-i-ben yn gofyn am ddatrys materion tystysgrifau ar gyfer { $count } derbynnydd.
+        [many] Mae amgryptio pen-i-ben yn gofyn am ddatrys materion tystysgrifau ar gyfer { $count } derbynnydd.
+       *[other] Mae amgryptio pen-i-ben yn gofyn am ddatrys materion tystysgrifau ar gyfer { $count } derbynnydd.
+    }
+key-notification-disable-encryption =
+    .label = Peidio ag Amgryptio
+    .accesskey = P
+    .tooltiptext = Analluogi amgryptio pen-i-ben
+key-notification-resolve =
+    .label = Datrys...
+    .accesskey = D
+    .tooltiptext = Agor Cynorthwydd Allweddi OpenPGP
+can-encrypt-smime-notification = Mae amgryptio S/MIME o ben-i-ben yn bosibl.
+can-encrypt-openpgp-notification = Mae amgryptio S/MIME o ben-i-ben yn bosibl.
+can-e2e-encrypt-button =
+    .label = Amgryptio
+    .accesskey = A
+
+## Addressing Area
+
+to-address-row-label =
+    .value = At
+#   $key (String) - the shortcut key for this field
+show-to-row-main-menuitem =
+    .label = I Faes
+    .accesskey = F
+    .acceltext = { ctrl-cmd-shift-pretty-prefix }{ $key }
+# No acceltext should be shown.
+# The label should match the show-to-row-button text.
+show-to-row-extra-menuitem =
+    .label = At
+    .accesskey = A
+#   $key (String) - the shortcut key for this field
+show-to-row-button = At
+    .title = Dangos i Faes ({ ctrl-cmd-shift-pretty-prefix }{ $key })
+cc-address-row-label =
+    .value = Cc
+#   $key (String) - the shortcut key for this field
+show-cc-row-main-menuitem =
+    .label = Maes Cc
+    .accesskey = C
+    .acceltext = { ctrl-cmd-shift-pretty-prefix }{ $key }
+# No acceltext should be shown.
+# The label should match the show-cc-row-button text.
+show-cc-row-extra-menuitem =
+    .label = Cc
+    .accesskey = C
+#   $key (String) - the shortcut key for this field
+show-cc-row-button = Cc
+    .title = Dangos Maes Cc ({ ctrl-cmd-shift-pretty-prefix }{ $key })
+bcc-address-row-label =
+    .value = Bcc
+#   $key (String) - the shortcut key for this field
+show-bcc-row-main-menuitem =
+    .label = Maes Bcc
+    .accesskey = B
+    .acceltext = { ctrl-cmd-shift-pretty-prefix }{ $key }
+# No acceltext should be shown.
+# The label should match the show-bcc-row-button text.
+show-bcc-row-extra-menuitem =
+    .label = Bcc
+    .accesskey = B
+#   $key (String) - the shortcut key for this field
+show-bcc-row-button = Bcc
+    .title = Dangos Maes Bcc ({ ctrl-cmd-shift-pretty-prefix }{ $key })
+extra-address-rows-menu-button =
+    .title = Meysydd cyfeiriadau eraill i'w dangos
+#   $count (Number) - the count of addresses in the "To" and "Cc" fields.
+many-public-recipients-notice =
+    { $count ->
+        [zero] Nid oes gan eich neges unrhyw dderbynydd.
+        [one] osgoi datgelu derbynwyr trwy ddefnyddio Bcc yn lle.
+        [two] Bydd y  { $count } derbyniwr yn At a Cc yn gweld cyfeiriad ei gilydd. Gallwch osgoi datgelu derbynwyr trwy ddefnyddio Bcc yn lle.
+        [few] Bydd y  { $count } derbyniwr yn At a Cc yn gweld cyfeiriad ei gilydd. Gallwch osgoi datgelu derbynwyr trwy ddefnyddio Bcc yn lle.
+        [many] Bydd y  { $count } derbyniwr yn At a Cc yn gweld cyfeiriad ei gilydd. Gallwch osgoi datgelu derbynwyr trwy ddefnyddio Bcc yn lle.
+       *[other] Bydd y  { $count } derbyniwr yn At a Cc yn gweld cyfeiriad ei gilydd. Gallwch osgoi datgelu derbynwyr trwy ddefnyddio Bcc yn lle.
+    }
+public-recipients-notice-single = Mae gan eich neges dderbynnydd cyhoeddus. Gallwch osgoi datgelu'r derbynnydd trwy ddefnyddio Bcc yn lle hynny.
+# Variables:
+# $count (Number) - the count of addresses in the "To" and "Cc" fields.
+public-recipients-notice-multi =
+    { $count ->
+        [zero] Ni fydd  { $count } derbyniwr yn At a Cc weld cyfeiriad ei gilydd. Gallwch osgoi datgelu derbynwyr trwy ddefnyddio Bcc yn lle.
+        [one] Bydd yr  { $count } derbyniwr yn At a Cc weld cyfeiriad ei gilydd. Gallwch osgoi datgelu derbynwyr trwy ddefnyddio Bcc yn lle.
+        [two] Bydd y  { $count } dderbyniwr yn At a Cc weld cyfeiriad ei gilydd. Gallwch osgoi datgelu derbynwyr trwy ddefnyddio Bcc yn lle.
+        [few] Bydd y  { $count } derbyniwr yn At a Cc weld cyfeiriad ei gilydd. Gallwch osgoi datgelu derbynwyr trwy ddefnyddio Bcc yn lle.
+        [many] Bydd y  { $count } derbyniwr yn At a Cc weld cyfeiriad ei gilydd. Gallwch osgoi datgelu derbynwyr trwy ddefnyddio Bcc yn lle.
+       *[other] Bydd y  { $count } derbyniwr yn At a Cc weld cyfeiriad ei gilydd. Gallwch osgoi datgelu derbynwyr trwy ddefnyddio Bcc yn lle.
+    }
+many-public-recipients-bcc =
+    .label = Defnyddio Bcc yn lle hynny
+    .accesskey = D
+many-public-recipients-ignore =
+    .label = Cadw Derbynwyr yn Gyhoeddus
+    .accesskey = G
+many-public-recipients-prompt-title = Gormod o Dderbynwyr Cyhoeddus
+#   $count (Number) - the count of addresses in the public recipients fields.
+many-public-recipients-prompt-msg =
+    { $count ->
+        [zero] Nid oes gan eich neges unrhyw dderbyniwr.
+        [one] Mae gan eich neges dderbynwyr cyhoeddus. Gall hyn fod yn bryder preifatrwydd. Gallwch osgoi datgelu derbynwyr trwy symud derbynwyr o At /Cc i Bcc yn lle.
+        [two] Mae gan eich neges { $count } derbynwyr cyhoeddus, a fydd yn gallu gweld cyfeiriadau ei gilydd. Gall hyn fod yn bryder preifatrwydd. Gallwch osgoi datgelu derbynwyr trwy symud derbynwyr o At /Cc i Bcc yn lle.
+        [few] Mae gan eich neges { $count } derbynwyr cyhoeddus, a fydd yn gallu gweld cyfeiriadau ei gilydd. Gall hyn fod yn bryder preifatrwydd. Gallwch osgoi datgelu derbynwyr trwy symud derbynwyr o At /Cc i Bcc yn lle.
+        [many] Mae gan eich neges { $count } derbynwyr cyhoeddus, a fydd yn gallu gweld cyfeiriadau ei gilydd. Gall hyn fod yn bryder preifatrwydd. Gallwch osgoi datgelu derbynwyr trwy symud derbynwyr o At /Cc i Bcc yn lle.
+       *[other] Mae gan eich neges { $count } derbynwyr cyhoeddus, a fydd yn gallu gweld cyfeiriadau ei gilydd. Gall hyn fod yn bryder preifatrwydd. Gallwch osgoi datgelu derbynwyr trwy symud derbynwyr o At /Cc i Bcc yn lle.
+    }
+many-public-recipients-prompt-cancel = Diddymu Anfon
+many-public-recipients-prompt-send = Anfonwch Beth Bynnag
+
+## Notifications
+
+# Variables:
+# $identity (string) - The name of the used identity, most likely an email address.
+compose-missing-identity-warning = Methu canfod hunaniaeth unigryw sy'n cyd-fynd a'r cyfeiriad Oddi wrth. Bydd y neges yn cael ei hanfon gan ddefnyddio'r maes Oddi wrth cyfredol a'r gosodiadau o hunaniaeth { $identity }.
+encrypted-bcc-warning = Wrth anfon neges wedi'i hamgryptio, nid yw'r derbynwyr yn Bcc wedi'u cuddio'n llawn. Efallai y bydd pob derbynnydd yn gallu eu hadnabod.
+encrypted-bcc-ignore-button = Wedi Deall
+auto-disable-e2ee-warning = Analluogwyd amgryptio pen-i-ben y neges hon yn awtomatig.
+
+## Editing
+
+
+# Tools
+
+compose-tool-button-remove-text-styling =
+    .tooltiptext = Tynnu Steilio Testun
+
+## Filelink
+
+# A text used in a tooltip of Filelink attachments, whose account has been
+# removed or is unknown.
+cloud-file-unknown-account-tooltip = Wedi'i lwytho i gyfrif Filelink anhysbys.
+
+# Placeholder file
+
+# Title for the html placeholder file.
+# $filename - name of the file
+cloud-file-placeholder-title = { $filename } - Atodiad Filelink
+# A text describing that the file was attached as a Filelink and can be downloaded
+# from the link shown below.
+# $filename - name of the file
+cloud-file-placeholder-intro = Atodwyd y ffeil { $filename } fel Filelink. Mae modd ei lwytho i lawr o'r ddolen isod.
+
+# Template
+
+# A line of text describing how many uploaded files have been appended to this
+# message. Emphasis should be on sharing as opposed to attaching. This item is
+# used as a header to a list, hence the colon.
+# Variables:
+# $count (Number) - Number of files.
+cloud-file-count-header =
+    { $count ->
+        [zero] Rwyf wedi cysylltu { $count } ffeil i'r e-bost hwn:
+        [one] Rwyf wedi cysylltu { $count } ffeil i'r e-bost hwn:
+        [two] Rwyf wedi cysylltu { $count } ffeil i'r e-bost hwn:
+        [few] Rwyf wedi cysylltu { $count } ffeil i'r e-bost hwn:
+        [many] Rwyf wedi cysylltu { $count } ffeil i'r e-bost hwn:
+       *[other] Rwyf wedi cysylltu { $count } ffeil i'r e-bost hwn:
+    }
+# A text used in a footer, instructing the reader where to find additional
+# information about the used service provider.
+# $link (string) - html a-tag for a link pointing to the web page of the provider
+cloud-file-service-provider-footer-single = Dysgu rhagor am { $link }.
+# A text used in a footer, instructing the reader where to find additional
+# information about the used service providers. Links for the used providers are
+# split into a comma separated list of the first n-1 providers and a single entry
+# at the end.
+# $firstLinks (string) - comma separated list of html a-tags pointing to web pages
+#                        of the first n-1 used providers
+# $lastLink (string) - html a-tag pointing the web page of the n-th used provider
+cloud-file-service-provider-footer-multiple = Dysgu rhagor am { $firstLinks } a { $lastLink }.
+# Tooltip for an icon, indicating that the link is protected by a password.
+cloud-file-tooltip-password-protected-link = Dolen wedi'i diogelu gan gyfrinair
+# Used in a list of stats about a specific file
+# Service - the used service provider to host the file (Filelink Service: BOX.com)
+# Size - the size of the file (Size: 4.2 MB)
+# Link - the link to the file (Link: https://some.provider.com)
+# Expiry Date - stating the date the link will expire (Expiry Date: 12.12.2022)
+# Download Limit - stating the maximum allowed downloads, before the link becomes invalid
+#                  (Download Limit: 6)
+cloud-file-template-service-name = Gwasanaeth Filelink:
+cloud-file-template-size = Maint:
+cloud-file-template-link = Dolen:
+cloud-file-template-password-protected-link = Dolen wedi'i Diogelu gan Gyfrinair
+cloud-file-template-expiry-date = Dyddiad Dod i Ben:
+cloud-file-template-download-limit = Terfyn Llwytho i Lawr:
+
+# Messages
+
+cloud-file-connection-error-title = Gwall Cysylltiad
+# Variables:
+# $provider (string) - name of the online storage service that reported the error
+cloud-file-connection-error = Mae { -brand-short-name } all-lein. Methu cysylltu â { $provider }.
+# Variables:
+# $provider (string) - name of the online storage service that reported the error
+# $filename (string) - name of the file that was uploaded and caused the error
+cloud-file-upload-error-with-custom-message-title = Methodd Llwytho { $filename } i { $provider }
+cloud-file-rename-error-title = Gwall Ail-enwi
+# Variables:
+# $provider (string) - name of the online storage service that reported the error
+# $filename (string) - name of the file that was renamed and caused the error
+cloud-file-rename-error = Bu anhawster wrth ailenwi { $filename } ar { $provider }.
+# Variables:
+# $provider (string) - name of the online storage service that reported the error
+# $filename (string) - name of the file that was renamed and caused the error
+cloud-file-rename-error-with-custom-message-title = Methodd ail-enwi { $filename } ar { $provider }
+# Variables:
+# $provider (string) - name of the online storage service that reported the error
+cloud-file-rename-not-supported = Nid yw { $provider } yn cefnogi ailenwi ffeiliau sydd eisoes wedi'u llwytho i fyny.
+cloud-file-attachment-error-title = Gwall Atodi Filelink
+# Variables:
+# $filename (string) - name of the file that was renamed and caused the error
+cloud-file-attachment-error = Wedi methu diweddaru'r atodiad Filelink { $filename }, oherwydd bod ei ffeil leol wedi'i symud neu ei dileu.
+cloud-file-account-error-title = Gwall Cyfrif Filelink
+# Variables:
+# $filename (string) - name of the file that was renamed and caused the error
+cloud-file-account-error = Wedi methu diweddaru'r atodiad Filelink { $filename }, oherwydd bod ei ffeil leol wedi'i symud neu ei dileu.
+
+## Link Preview
+
+link-preview-title = Rhagolwg Dolen
+link-preview-description = Gall { -brand-short-name } ychwanegu rhagolwg wedi'i fewnblannu wrth ludo dolenni.
+link-preview-autoadd = Ychwanegu ragolygon dolenni'n awtomatig pan fo modd
+link-preview-replace-now = Ychwanegu Rhagolwg Dolen ar gyfer y ddolen hon?
+link-preview-yes-replace = Iawn
+
+## Dictionary selection popup
+
+spell-add-dictionaries =
+    .label = Ychwanegu Geiriaduron…
+    .accesskey = Y
diff --git a/thunderbird-l10n/cy/localization/cy/messenger/migration.ftl b/thunderbird-l10n/cy/localization/cy/messenger/migration.ftl
new file mode 100644
index 0000000000..302a661820
--- /dev/null
+++ b/thunderbird-l10n/cy/localization/cy/messenger/migration.ftl
@@ -0,0 +1,15 @@
+# This Source Code Form is subject to the terms of the Mozilla Public
+# License, v. 2.0. If a copy of the MPL was not distributed with this
+# file, you can obtain one at http://mozilla.org/MPL/2.0/.
+
+migration-progress-header = Yn cael { -brand-short-name } yn barod…
+
+## Migration tasks
+
+
+# These strings are displayed to the user if a migration is taking a long time.
+# They should be short (no more than a handful of words) and in the present tense.
+
+migration-task-test-fast = Yn profi newid cyflym
+migration-task-test-slow = Yn profi newid araf
+migration-task-test-progress = Yn profi'r bar cynnydd
diff --git a/thunderbird-l10n/cy/localization/cy/messenger/multimessageview.ftl b/thunderbird-l10n/cy/localization/cy/messenger/multimessageview.ftl
new file mode 100644
index 0000000000..100b4aa756
--- /dev/null
+++ b/thunderbird-l10n/cy/localization/cy/messenger/multimessageview.ftl
@@ -0,0 +1,14 @@
+# This Source Code Form is subject to the terms of the Mozilla Public
+# License, v. 2.0. If a copy of the MPL was not distributed with this
+# file, You can obtain one at http://mozilla.org/MPL/2.0/.
+
+multi-message-window-title =
+    .title = Crynodeb Neges
+selected-messages-label =
+    .label = Negeseuon wedi'u Dewis
+multi-message-archive-button =
+    .label = Archifo
+    .tooltiptext = Archifo
+multi-message-delete-button =
+    .label = Dileu
+    .tooltiptext = Dileu
diff --git a/thunderbird-l10n/cy/localization/cy/messenger/openpgp/backupKeyPassword.ftl b/thunderbird-l10n/cy/localization/cy/messenger/openpgp/backupKeyPassword.ftl
new file mode 100644
index 0000000000..1feb13b189
--- /dev/null
+++ b/thunderbird-l10n/cy/localization/cy/messenger/openpgp/backupKeyPassword.ftl
@@ -0,0 +1,17 @@
+# This Source Code Form is subject to the terms of the Mozilla Public
+# License, v. 2.0. If a copy of the MPL was not distributed with this
+# file, You can obtain one at http://mozilla.org/MPL/2.0/.
+
+set-password-window =
+    .title = Dewiswch gyfrinair i wneud copi wrth gefn o'ch Allwedd OpenPGP
+set-password-window-title = Dewiswch gyfrinair i wneud copi wrth gefn o'ch Allwedd OpenPGP
+set-password-legend = Dewiswch Gyfrinair
+set-password-message = Bydd y cyfrinair wrth gefn yma'n diogelu'r allwedd gyfrinachol OpenPGP wrth gefn rydych ar fin ei chreu.  Rhaid gosod y cyfrinair i barhau gyda'r ffeil wrth gefn.
+set-password-backup-pw =
+    .value = Cyfrinair wrth gefn Allwedd Cyfrinachol:
+set-password-repeat-backup-pw =
+    .value = Cyfrinair wrth gefn Allwedd Cyfrinachol (eto):
+set-password-backup-pw-label = Cyfrinair wrth gefn Allwedd Cyfrinachol:
+set-password-backup-pw2-label = Cyfrinair wrth gefn Allwedd Cyfrinachol (eto):
+set-password-reminder = <b>Pwysig!</b> Os byddwch yn anghofio eich cyfrinair diogelwch wrth gefn, ni fydd modd i chi adfer y ffeil wrth gefn yma eto.  Cofnodwch hwn mewn man diogel.
+password-quality-meter = Mesurydd ansawdd cyfrinair
diff --git a/thunderbird-l10n/cy/localization/cy/messenger/openpgp/changeExpiryDlg.ftl b/thunderbird-l10n/cy/localization/cy/messenger/openpgp/changeExpiryDlg.ftl
new file mode 100644
index 0000000000..46993a923e
--- /dev/null
+++ b/thunderbird-l10n/cy/localization/cy/messenger/openpgp/changeExpiryDlg.ftl
@@ -0,0 +1,24 @@
+# This Source Code Form is subject to the terms of the Mozilla Public
+# License, v. 2.0. If a copy of the MPL was not distributed with this
+# file, You can obtain one at http://mozilla.org/MPL/2.0/.
+
+openpgp-change-key-expiry-title =
+    .title = Newid Dod i Ben yr Allwedd
+openpgp-change-expiry-title = Newid Dod i Ben yr Allwedd
+# Variables:
+# $date (String) - Date the key is expiring on.
+info-will-expire = Mae'r allwedd hon wedi'i ffurfweddu i ddod i ben ar { $date }
+info-already-expired = Mae'r allwedd hon eisoes wedi dod i ben.
+info-does-not-expire = Mae'r allwedd hon wedi'i ffurfweddu i beidio byth â dod i ben.
+info-explanation-1 = <b>Ar ôl i allwedd ddod i ben</b>, nid yw bellach yn bosibl ei defnyddio ar gyfer amgryptio neu arwyddo digidol.
+info-explanation-2 = I ddefnyddio'r allwedd hon am gyfnod hirach, newidiwch ei dyddiad dod i ben, ac yna rhannwch yr allwedd gyhoeddus gyda'ch partneriaid sgwrsio eto.
+expire-dont-change =
+    .label = Peidiwch â newid y dyddiad dod i ben
+expire-never-label =
+    .label = Ni fydd yr allwedd byth yn dod i ben
+expire-in-label =
+    .label = Bydd yr allwedd yn dod i ben ar:
+expire-in-months = Mis
+expire-no-change-label = Peidiwch â newid y dyddiad dod i ben
+expire-in-time-label = Bydd yr allwedd yn dod i ben ar:
+expire-never-expire-label = Ni fydd yr allwedd byth yn dod i ben
diff --git a/thunderbird-l10n/cy/localization/cy/messenger/openpgp/composeKeyStatus.ftl b/thunderbird-l10n/cy/localization/cy/messenger/openpgp/composeKeyStatus.ftl
new file mode 100644
index 0000000000..3b06f8c6c0
--- /dev/null
+++ b/thunderbird-l10n/cy/localization/cy/messenger/openpgp/composeKeyStatus.ftl
@@ -0,0 +1,30 @@
+# This Source Code Form is subject to the terms of the Mozilla Public
+# License, v. 2.0. If a copy of the MPL was not distributed with this
+# file, You can obtain one at http://mozilla.org/MPL/2.0/.
+
+openpgp-compose-key-status-intro-need-keys = I anfon neges wedi'i hamgryptio o ben-i-ben, rhaid i chi gael a derbyn allwedd gyhoeddus ar gyfer pob derbynnydd.
+openpgp-compose-key-status-keys-heading = Argaeledd allweddi OpenPGP:
+openpgp-compose-key-status-title =
+    .title = Diogelwch Negeseuon OpenPGP
+openpgp-compose-key-status-recipient =
+    .label = Derbynnydd
+openpgp-compose-key-status-status =
+    .label = Statws
+openpgp-compose-key-status-open-details = Rheoli allweddi ar gyfer derbynnydd dewisol...
+openpgp-recip-good = iawn
+openpgp-recip-missing = dim allwedd ar gael
+openpgp-recip-none-accepted = dim allwedd wedi'i derbyn
+openpgp-compose-general-info-alias = Mae { -brand-short-name } fel arfer yn disgwyl bod allwedd gyhoeddus y derbynnydd yn cynnwys ID defnyddiwr gyda chyfeiriad e-bost sy'n cyfateb. Mae modd diystyru hyn trwy ddefnyddio rheolau alias derbynnydd OpenPGP.
+openpgp-compose-general-info-alias-learn-more = Dysgu rhagor
+# Variables:
+# $count (Number) - Number of alias keys for a recipient.
+openpgp-compose-alias-status-direct =
+    { $count ->
+        [zero] heb ei fapio i allweddi alias
+        [one] wedi'i fapio i { $count } allwedd alias
+        [two] wedi'i fapio i { $count } allwedd alias
+        [few] wedi'i fapio i { $count } allwedd alias
+        [many] wedi'i fapio i { $count }allwedd alias
+       *[other] wedi'i fapio i { $count } allwedd alias
+    }
+openpgp-compose-alias-status-error = allwedd alias nad oes modd ei ddefnyddio/ddim ar gael
diff --git a/thunderbird-l10n/cy/localization/cy/messenger/openpgp/keyAssistant.ftl b/thunderbird-l10n/cy/localization/cy/messenger/openpgp/keyAssistant.ftl
new file mode 100644
index 0000000000..70f54533d7
--- /dev/null
+++ b/thunderbird-l10n/cy/localization/cy/messenger/openpgp/keyAssistant.ftl
@@ -0,0 +1,151 @@
+# This Source Code Form is subject to the terms of the Mozilla Public
+# License, v. 2.0. If a copy of the MPL was not distributed with this
+# file, You can obtain one at http://mozilla.org/MPL/2.0/.
+
+openpgp-key-assistant-title = Cynorthwy-ydd Allwedd OpenPGP
+openpgp-key-assistant-rogue-warning = Ceisiwch osgoi derbyn allwedd ffug. Er mwyn sicrhau eich bod wedi cael yr allwedd gywir dylech ei wirio. <a data-l10n-name="openpgp-link">Dysgu rhagor…</a>
+
+## Encryption status
+
+openpgp-key-assistant-recipients-issue-header = Methu Amgryptio
+# Variables:
+# $count (Number) - The number of recipients that need attention.
+openpgp-key-assistant-recipients-issue-description =
+    { $count ->
+        [zero] I amgryptio, rhaid i chi gael a derbyn allweddi defnyddiadwy ar gyfer { $count } derbynwyr. <a data-l10n-name="openpgp-link">Dysgu rhagor…</a>
+        [one] I amgryptio, rhaid i chi gael a derbyn allwedd ddefnyddiadwy ar gyfer un derbynydd. <a data-l10n-name="openpgp-link">Dysgu rhagor…</a>
+        [two] I amgryptio, rhaid i chi gael a derbyn allweddi defnyddiadwy ar gyfer { $count } derbynwyr. <a data-l10n-name="openpgp-link">Dysgu rhagor…</a>
+        [few] I amgryptio, rhaid i chi gael a derbyn allweddi defnyddiadwy ar gyfer { $count } derbynwyr. <a data-l10n-name="openpgp-link">Dysgu rhagor…</a>
+        [many] I amgryptio, rhaid i chi gael a derbyn allweddi defnyddiadwy ar gyfer { $count } derbynwyr. <a data-l10n-name="openpgp-link">Dysgu rhagor…</a>
+       *[other] I amgryptio, rhaid i chi gael a derbyn allweddi defnyddiadwy ar gyfer { $count } derbynwyr. <a data-l10n-name="openpgp-link">Dysgu rhagor…</a>
+    }
+openpgp-key-assistant-info-alias = Mae { -brand-short-name } fel arfer yn disgwyl bod allwedd gyhoeddus y derbynnydd yn cynnwys ID defnyddiwr gyda chyfeiriad e-bost sy'n cyfateb. Mae modd diystyru hyn trwy ddefnyddio rheolau alias derbynnydd OpenPGP. <a data-l10n-name="openpgp-link">Dysgu rhagor…</a>
+# Variables:
+# $count (Number) - The number of recipients that need attention.
+openpgp-key-assistant-recipients-description =
+    { $count ->
+        [zero] Mae gennych eisoes allweddi defnyddiadwy a derbyniol ar gyfer { $count } o dderbynwyr .
+        [one] Mae gennych eisoes allweddi defnyddiadwy a derbyniol ar gyfer un derbynydd.
+        [two] Mae gennych eisoes allweddi defnyddiadwy a derbyniol ar gyfer { $count } dderbynydd.
+        [few] Mae gennych eisoes allweddi defnyddiadwy a derbyniol ar gyfer { $count } derbynydd.
+        [many] Mae gennych eisoes allweddi defnyddiadwy a derbyniol ar gyfer { $count } derbynydd..
+       *[other] Mae gennych eisoes allweddi defnyddiadwy a derbyniol ar gyfer { $count } derbynydd..
+    }
+openpgp-key-assistant-recipients-description-no-issues = Mae modd amgryptio'r neges hon. Mae gennych allweddi defnyddiadwy a derbyniol ar gyfer pob derbynnydd.
+
+## Resolve section
+
+# Variables:
+# $recipient (String) - The email address of the recipient needing resolution.
+# $numKeys (Number) - The number of keys.
+openpgp-key-assistant-resolve-title =
+    { $numKeys ->
+        [zero] Mae { -brand-short-name } wedi dod o hyd i'r allweddi canlynol ar gyfer { $recipient } .
+        [one] Mae { -brand-short-name } wedi dod o hyd i'r allwedd ganlynol ar gyfer { $recipient } .
+        [two] Mae { -brand-short-name } wedi dod o hyd i'r allweddi canlynol ar gyfer { $recipient } .
+        [few] Mae { -brand-short-name } wedi dod o hyd i'r allweddi canlynol ar gyfer { $recipient } .
+        [many] Mae { -brand-short-name } wedi dod o hyd i'r allweddi canlynol ar gyfer { $recipient } .
+       *[other] Mae { -brand-short-name } wedi dod o hyd i'r allweddi canlynol ar gyfer { $recipient } .
+    }
+openpgp-key-assistant-valid-description = Dewiswch yr allwedd rydych am ei dderbyn
+# Variables:
+# $numKeys (Number) - The number of available keys.
+openpgp-key-assistant-invalid-title =
+    { $numKeys ->
+        [zero] Nid oes modd defnyddio'r allweddi canlynol, oni bai eich bod wedi cael diweddariad.
+        [one] Nid oes modd defnyddio'r allwedd ganlynol, oni bai eich bod wedi cael diweddariad.
+        [two] Nid oes modd defnyddio'r allweddi canlynol, oni bai eich bod wedi cael diweddariad.
+        [few] Nid oes modd defnyddio'r allweddi canlynol, oni bai eich bod wedi cael diweddariad.
+        [many] Nid oes modd defnyddio'r allweddi canlynol, oni bai eich bod wedi cael diweddariad.
+       *[other] Nid oes modd defnyddio'r allweddi canlynol, oni bai eich bod wedi cael diweddariad.
+    }
+openpgp-key-assistant-no-key-available = Dim allwedd ar gael.
+openpgp-key-assistant-multiple-keys = Mae nifer o allweddi ar gael.
+# Variables:
+# $count (Number) - The number of unaccepted keys.
+openpgp-key-assistant-key-unaccepted =
+    { $count ->
+        [zero] Mae nifer o allweddi ar gael, ond nid oes yr un ohonynt wedi'u derbyn eto.
+        [one] Mae allwedd ar gael, ond nid yw wedi'i dderbyn eto.
+        [two] Mae nifer o allweddi ar gael, ond nid oes yr un ohonynt wedi'u derbyn eto.
+        [few] Mae nifer o allweddi ar gael, ond nid oes yr un ohonynt wedi'u derbyn eto.
+        [many] Mae nifer o allweddi ar gael, ond nid oes yr un ohonynt wedi'u derbyn eto.
+       *[other] Mae nifer o allweddi ar gael, ond nid oes yr un ohonynt wedi'u derbyn eto.
+    }
+# Variables:
+# $date (String) - The expiration date of the key.
+openpgp-key-assistant-key-accepted-expired = Mae allwedd sydd wedi'i dderbyn wedi dod i ben ar { $date }.
+openpgp-key-assistant-keys-accepted-expired = Mae nifer o allweddi â dderbyniwyd wedi dod i ben.
+# Variables:
+# $date (String) - The expiration date of the key.
+openpgp-key-assistant-this-key-accepted-expired = Cafodd yr allwedd hon ei derbyn cynt ond daeth i ben ar { $date }.
+# Variables:
+# $date (String) - The expiration date of the key.
+openpgp-key-assistant-key-unaccepted-expired-one = Daeth yr allwedd i ben ar { $date }.
+openpgp-key-assistant-key-unaccepted-expired-many = Mae nifer o allweddi wedi dod i ben.
+openpgp-key-assistant-key-fingerprint = Bysbrint
+# Variables:
+# $count (Number) - Number of key sources.
+openpgp-key-assistant-key-source =
+    { $count ->
+        [zero] Ffynonellau
+        [one] Ffynhonnell
+        [two] Ffynhonnell
+        [few] Ffynhonnell
+        [many] Ffynhonnell
+       *[other] Ffynhonnell
+    }
+openpgp-key-assistant-key-collected-attachment = atodiad e-bost
+# Autocrypt is the name of a standard.
+openpgp-key-assistant-key-collected-autocrypt = Pennyn awtoamgrypt
+openpgp-key-assistant-key-collected-keyserver = gweinydd allweddi
+# Web Key Directory (WKD) is a concept.
+openpgp-key-assistant-key-collected-wkd = Cyfeiriadur Allweddi Gwe
+# Do not translate GnuPG, it's a name of other software.
+openpgp-key-assistant-key-collected-gnupg = Cylch allweddi GnuPG
+# Variables:
+# $count (Number) - Number of found keys.
+openpgp-key-assistant-keys-has-collected =
+    { $count ->
+        [zero] Cafodd nifer o allweddi eu canfod, ond nid oes yr un ohonyn nhw wedi'u derbyn eto.
+        [one] Cafodd un allwedd ei ganfod, ond nid nid yw wedi'i dderbyn eto.
+        [two] Cafodd nifer o allweddi eu canfod, ond nid oes yr un ohonyn nhw wedi'u derbyn eto.
+        [few] Cafodd nifer o allweddi eu canfod, ond nid oes yr un ohonyn nhw wedi'u derbyn eto.
+        [many] Cafodd nifer o allweddi eu canfod, ond nid oes yr un ohonyn nhw wedi'u derbyn eto.
+       *[other] Cafodd nifer o allweddi eu canfod, ond nid oes yr un ohonyn nhw wedi'u derbyn eto.
+    }
+openpgp-key-assistant-key-rejected = Cafodd yr allwedd hon ei gwrthod gynt.
+openpgp-key-assistant-key-accepted-other = Cafodd yr  allwedd hon ei derbyn gynt ar gyfer cyfeiriad e-bost gwahanol.
+# Variables:
+# $recipient (String) - The email address of the recipient needing resolution.
+openpgp-key-assistant-resolve-discover-info = Darganfod allweddi ychwanegol neu rhai wedi'u diweddaru ar gyfer { $recipient } ar-lein, neu eu mewnforio o ffeil.
+
+## Discovery section
+
+openpgp-key-assistant-discover-title = Wrthi'n darganfod ar-lein.
+# Variables:
+# $recipient (String) - The email address which we're discovering keys.
+openpgp-key-assistant-discover-keys = Wrthi'n darganfod allweddi ar gyfer { $recipient }…
+# Variables:
+# $recipient (String) - The email address which we're discovering keys.
+openpgp-key-assistant-expired-key-update =
+    Cafwyd hyd i ddiweddariad ar gyfer un o'r allweddi a dderbyniwyd gynt ar gyfer { $recipient }.
+    Mae modd ei ddefnyddio nawr gan nad yw bellach wedi dod i ben.
+
+## Dialog buttons
+
+openpgp-key-assistant-discover-online-button = Darganfod Allweddi Cyhoeddus Ar-lein…
+openpgp-key-assistant-import-keys-button = Mewnforio Allweddi Cyhoeddus o'r Ffeil…
+openpgp-key-assistant-issue-resolve-button = Datrys...
+openpgp-key-assistant-view-key-button = Gweld Allwedd…
+openpgp-key-assistant-recipients-show-button = Dangos
+openpgp-key-assistant-recipients-hide-button = Cuddio
+openpgp-key-assistant-cancel-button = Diddymu
+openpgp-key-assistant-back-button = Nôl
+openpgp-key-assistant-accept-button = Derbyn
+openpgp-key-assistant-close-button = Cau
+openpgp-key-assistant-disable-button = Analluogi Amgryptio
+openpgp-key-assistant-confirm-button = Anfon Wedi'i Amgryptio
+# Variables:
+# $date (String) - The key creation date.
+openpgp-key-assistant-key-created = crëwyd ar { $date }
diff --git a/thunderbird-l10n/cy/localization/cy/messenger/openpgp/keyWizard.ftl b/thunderbird-l10n/cy/localization/cy/messenger/openpgp/keyWizard.ftl
new file mode 100644
index 0000000000..6db3ff97fb
--- /dev/null
+++ b/thunderbird-l10n/cy/localization/cy/messenger/openpgp/keyWizard.ftl
@@ -0,0 +1,144 @@
+# This Source Code Form is subject to the terms of the Mozilla Public
+# License, v. 2.0. If a copy of the MPL was not distributed with this
+# file, You can obtain one at http://mozilla.org/MPL/2.0/.
+
+#   $identity (String) - the email address of the currently selected identity
+key-wizard-dialog-window =
+    .title = Ychwanegu Allwedd OpenPGP Personol ar gyfer { $identity }
+key-wizard-button =
+    .buttonlabelaccept = Parhau
+    .buttonlabelhelp = Mynd nôl
+key-wizard-dialog =
+    .buttonlabelaccept = Parhau
+    .buttonlabelextra1 = Mynd nôl
+key-wizard-warning = <b>Os oes gennych allwedd bersonol bresennol</b> ar gyfer y cyfeiriad e-bost hwn, dylech ei fewnforio. Fel arall ni fydd gennych fynediad i'ch archifau o e-byst wedi'u hamgryptio, nac yn gallu darllen e-byst wedi'u hamgryptio rydych yn eu derbyn gan bobl sy'n dal i ddefnyddio'ch allwedd bresennol.
+key-wizard-learn-more = Dysgu rhagor
+radio-create-key =
+    .label = Creu Allwedd OpenPGP newydd
+    .accesskey = C
+radio-import-key =
+    .label = Mewnforio Allwedd OpenPGP cyfredol
+    .accesskey = M
+radio-gnupg-key =
+    .label = Defnyddio'ch allwedd allanol trwy GnuPG (e.e. o gerdyn clyfar)
+    .accesskey = D
+
+## Generate key section
+
+openpgp-generate-key-title = Cynhyrchu Allwedd OpenPGP
+openpgp-keygen-secret-protection = Diogelu Allwedd Cyfrinachol
+radio-keygen-no-protection =
+    .label = Heb ei ddiogelu
+radio-keygen-protect-primary-pass =
+    .label = Diogelu gyda'r Prif Gyfrinair
+radio-keygen-passphrase-protection =
+    .label = Diogelu gyda chyfrinymadrodd:
+openpgp-passphrase-repeat = Cadarnhewch y cyfrinymadrodd:
+openpgp-generate-key-info = <b>Gall cynhyrchu allweddol gymryd rhai munudau i'w gwblhau.</b> Peidiwch â gadael y rhaglen tra bo'r allwedd yn cael ei gynhyrchu. Bydd pori neu berfformio gweithrediadau disg-ddwys yn ystod cynhyrchu'r allwedd yn ailgyflenwi'r 'gronfa ar hap' ac yn cyflymu'r broses. Cewch eich rhybuddio pan fydd cynhyrchu'r allweddol wedi'i gwblhau.
+openpgp-keygen-expiry-title = Allwedd yn dod i ben
+openpgp-keygen-expiry-description = Diffiniwch amser dod i ben eich allwedd sydd newydd ei chynhyrchu. Yn ddiweddarach, gallwch reoli'r dyddiad i'w ymestyn os oes angen.
+radio-keygen-expiry =
+    .label = Allwedd yn dod i ben ymhen
+    .accesskey = l
+radio-keygen-no-expiry =
+    .label = Nid yw'r allwedd yn dod i ben
+    .accesskey = N
+openpgp-keygen-days-label =
+    .label = diwrnod
+openpgp-keygen-months-label =
+    .label = mis
+openpgp-keygen-years-label =
+    .label = blwyddyn
+openpgp-keygen-advanced-title = Gosodiadau uwch
+openpgp-keygen-advanced-description = Rheoli gosodiadau uwch eich Allwedd OpenPGP.
+openpgp-keygen-keytype =
+    .value = Math o allwedd:
+    .accesskey = M
+openpgp-keygen-keysize =
+    .value = Maint yr allwedd:
+    .accesskey = a
+openpgp-keygen-type-rsa =
+    .label = RSA
+openpgp-keygen-type-ecc =
+    .label = ECC (Cromlin Eliptig)
+openpgp-keygen-button = Cynhyrchu allwedd
+openpgp-keygen-progress-title = Cynhyrchu eich Allwedd OpenPGP newydd ...
+openpgp-keygen-import-progress-title = Mewnforio eich Allweddi OpenPGP...
+openpgp-import-success = Allweddi OpenPGP wedi'u mewnforio'n llwyddiannus!
+openpgp-import-success-title = Cwblhewch y broses fewnforio
+openpgp-import-success-description = I ddechrau defnyddio'ch allwedd OpenPGP wedi'i fewnforio ar gyfer amgryptio e-bost, caewch y dialog hwn ac ewch i'ch Gosodiadau Cyfrif i'w ddewis.
+openpgp-keygen-confirm =
+    .label = Cadarnhau
+openpgp-keygen-dismiss =
+    .label = Diddymu
+openpgp-keygen-cancel =
+    .label = Diddymu'r broses ...
+openpgp-keygen-import-complete =
+    .label = Cau
+    .accesskey = C
+openpgp-keygen-missing-username = Nid oes enw wedi'i nodi ar gyfer y cyfrif cyfredol. Rhowch werth yn y maes "Eich enw" yng ngosodiadau'r cyfrif.
+openpgp-keygen-long-expiry = Nid oes modd i chi greu allwedd sy'n dod i ben mewn mwy na 100 mlynedd.
+openpgp-keygen-short-expiry = Rhaid i'ch allwedd fod yn ddilys am o leiaf un diwrnod.
+openpgp-keygen-ongoing = Eisoes wrthi'n cynhyrchu allwedd!
+openpgp-keygen-error-core = Methu cychwyn Gwasanaeth Craidd OpenPGP
+openpgp-keygen-error-failed = Yn annisgwyl, methwyd cynhyrchu allwedd OpenPGP
+#   $key (String) - the ID of the newly generated OpenPGP key
+openpgp-keygen-error-revocation = Crëwyd Allwedd OpenPGP yn llwyddiannus, ond methodd â chael dirymiad ar gyfer allwedd { $key }
+openpgp-keygen-abort-title = Atal cynhyrchu allwedd?
+openpgp-keygen-abort = Mae cynhyrchu allwedd OpenPGP ar y gweill ar hyn o bryd, a ydych chi'n siŵr eich bod am ei ddiddymu?
+#   $identity (String) - the name and email address of the currently selected identity
+openpgp-key-confirm = Cynhyrchu allwedd gyhoeddus a chyfrinachol ar gyfer { $identity }?
+
+## Import Key section
+
+openpgp-import-key-title = Mewnforio Allwedd OpenPGP personol sy'n bodoli eisoes
+openpgp-import-key-legend = Dewis ffeil a gadwyd wrth gefn.
+openpgp-import-key-description = Gallwch fewnforio allweddi personol a gafodd eu creu gyda meddalwedd OpenPGP arall.
+openpgp-import-key-info = Gall meddalwedd arall ddisgrifio allwedd bersonol gan ddefnyddio termau amgen fel eich allwedd eich hun, allwedd gyfrinachol, allwedd breifat neu bar o allweddi.
+#   $count (Number) - the number of keys found in the selected files
+openpgp-import-key-list-amount-2 =
+    { $count ->
+        [zero] Daeth { -brand-short-name } o hyd i { $count } allweddi y mae modd eu mewnforio.
+        [one] Daeth { -brand-short-name } o hyd i un allwedd y mae modd ei fewnforio.
+        [two] Daeth { -brand-short-name } o hyd i { $count } allweddi y mae modd eu mewnforio.
+        [few] Daeth { -brand-short-name } o hyd i { $count } allweddi y mae modd eu mewnforio.
+        [many] Daeth { -brand-short-name } o hyd i { $count } allweddi y mae modd eu mewnforio.
+       *[other] Daeth { -brand-short-name } o hyd i { $count } allweddi y mae modd eu mewnforio.
+    }
+openpgp-import-key-list-description = Cadarnhewch pa allweddi y mae modd eu trin fel eich allweddi personol. Dim ond allweddi y gwnaethoch chi eu creu eich hun ac sy'n dangos eich hunaniaeth eich hun y dylid eu defnyddio fel allweddi personol. Gallwch newid yr dewis hwn yn nes ymlaen yn y dialog Priodweddau Allweddi.
+openpgp-import-key-list-caption = Bydd allweddi sydd wedi'u marcio i'w trin fel Allweddi Personol yn cael eu rhestru yn yr adran Amgryptio Ben-i-Ben. Bydd y lleill ar gael y tu mewn i'r Rheolwr Allweddi.
+openpgp-import-keep-passphrases =
+    .label = Cadw diogelu cyfrinymadrodd ar gyfer allweddi cyfrinachol wedi'u mewnforio
+openpgp-passphrase-prompt-title = Mae angen cyfrinymadrodd
+#   $identity (String) - the id of the key being imported
+openpgp-passphrase-prompt = Rhowch y cyfrinymadrodd i ddatgloi'r allwedd ganlynol: { $key }
+openpgp-import-key-button =
+    .label = Dewis Ffeil i'w Mewnforio ...
+    .accesskey = D
+import-key-file = Mewnforio Ffeil Allwedd OpenPGP
+import-key-personal-checkbox =
+    .label = Trin yr allwedd hon fel Allwedd Bersonol
+gnupg-file = Ffeiliau GnuPG
+import-error-file-size = <b>Gwall!</b> Nid yw ffeiliau mwy na 5MB yn cael eu cefnogi.
+#   $error (String) - the reported error from the failed key import method
+import-error-failed = <b>Gwall!</b> Wedi methu mewnforio ffeil. { $error }
+#   $error (String) - the reported error from the failed key import method
+openpgp-import-keys-failed = <b>Gwall!</b> Wedi methu mewnforio allweddi. { $error }
+openpgp-import-identity-label = Hunaniaeth
+openpgp-import-fingerprint-label = Bysbrint
+openpgp-import-created-label = Crëwyd
+openpgp-import-bits-label = Didau
+openpgp-import-key-props =
+    .label = Priodweddau Allweddi
+    .accesskey = P
+
+## External Key section
+
+openpgp-external-key-title = Allwedd GnuPG Allanol
+openpgp-external-key-description = Ffurfweddu allwedd GnuPG allanol trwy nodi ID yr Allwedd
+openpgp-external-key-info = Yn ogystal, rhaid i chi ddefnyddio'r Rheolwr Allweddi i fewnforio a derbyn yr Allwedd Gyhoeddus gyfatebol.
+openpgp-external-key-warning = <b>Dim ond un Allwedd GnuPG allanol y gallwch chi ei ffurfweddu.</b> Bydd eich cofnod blaenorol yn cael ei ddisodli.
+openpgp-save-external-button = Cadw ID yr allwedd
+openpgp-external-key-label = ID Allwedd Gyfrinachol:
+openpgp-external-key-input =
+    .placeholder = 123456789341298340
diff --git a/thunderbird-l10n/cy/localization/cy/messenger/openpgp/msgReadStatus.ftl b/thunderbird-l10n/cy/localization/cy/messenger/openpgp/msgReadStatus.ftl
new file mode 100644
index 0000000000..a1245e5d9c
--- /dev/null
+++ b/thunderbird-l10n/cy/localization/cy/messenger/openpgp/msgReadStatus.ftl
@@ -0,0 +1,86 @@
+# This Source Code Form is subject to the terms of the Mozilla Public
+# License, v. 2.0. If a copy of the MPL was not distributed with this
+# file, You can obtain one at http://mozilla.org/MPL/2.0/.
+
+
+## Message Header Encryption Button
+
+message-header-show-security-info-key = D
+#   $type (String) - the shortcut key defined in the message-header-show-security-info-key
+message-security-button =
+    .title =
+        { PLATFORM() ->
+            [macos] Dangos Diogelwch Negeseuon (⌘ ⌥ { message-header-show-security-info-key })
+           *[other] Dangos Diogelwch Negeseuon (Ctrl+Alt+{ message-header-show-security-info-key }
+        }
+openpgp-view-signer-key =
+    .label = Gweld allwedd llofnodwr
+openpgp-view-your-encryption-key =
+    .label = Gweld eich allwedd dadgryptio
+openpgp-openpgp = OpenPGP
+openpgp-no-sig = Dim Llofnod Digidol
+openpgp-no-sig-info = Nid yw'r neges yn cynnwys llofnod digidol yr anfonwr. Mae absenoldeb y llofnod digidol yn golygu bod modd i'r neges ddod gan rywun sy'n cogio mai ei gyfeiriad e-bost yw hwn. Mae hefyd yn bosibl fod y neges wedi cael ei newid wrth deithio ar draws y rhwydwaith.
+openpgp-uncertain-sig = Llofnod Digidol Ansicr
+# Variables:
+# $date (String) - Date with time the signature was made in a short format.
+openpgp-uncertain-sig-with-date = Llofnod Digidol Ansicr - Wedi'i lofnodi ar { $date }
+openpgp-invalid-sig = Llofnod Digidol Annilys
+# Variables:
+# $date (String) - Date with time the signature was made in a short format.
+openpgp-invalid-sig-with-date = Llofnod Digidol Annilys - Wedi'i lofnodi ar { $date }
+openpgp-bad-date-sig = Gwrthdaro Dyddiad Llofnod
+# Variables:
+# $date (String) - Date with time the signature was made in a short format.
+openpgp-bad-date-sig-with-date = Gwrthdaro Dyddiad Llofnod - Llofnodwyd ar { $date }
+openpgp-good-sig = Llofnod Digidol Da
+# Variables:
+# $date (String) - Date with time the signature was made in a short format.
+openpgp-good-sig-with-date = Llofnod Digidol Dilys - Wedi'i lofnodi ar { $date }
+openpgp-sig-uncertain-no-key = Mae'r neges hon yn cynnwys llofnod digidol, ond mae'n ansicr a yw'n gywir. I wirio'r llofnod, mae angen i chi gael copi o allwedd gyhoeddus yr anfonwr.
+openpgp-sig-uncertain-uid-mismatch = Mae'r neges hon yn cynnwys llofnod digidol, ond canfuwyd diffyg cyfatebiaeth. Anfonwyd y neges o gyfeiriad e-bost nad yw'n cyd-fynd ag allwedd gyhoeddus y llofnodwr.
+openpgp-sig-uncertain-not-accepted = Mae'r neges hon yn cynnwys llofnod digidol, ond nid ydych wedi penderfynu eto a yw allwedd y llofnodwr yn dderbyniol i chi.
+openpgp-sig-invalid-rejected = Mae'r neges hon yn cynnwys llofnod digidol, ond rydych chi wedi penderfynu gwrthod allwedd y llofnodwr yn flaenorol.
+openpgp-sig-invalid-technical-problem = Mae'r neges hon yn cynnwys llofnod digidol, ond canfuwyd gwall technegol. Naill ai mae'r neges wedi'i llygru, neu mae'r neges wedi'i haddasu gan rywun arall.
+openpgp-sig-invalid-date-mismatch = Mae'r neges hon yn cynnwys llofnod digidol, ond ni wnaed y llofnod ar yr un pryd ag anfonwyd y neges e-bost. Gallai hyn fod yn ymgais i’ch twyllo gyda chynnwys o’r cyd-destun anghywir: e.e. cynnwys wedi'i ysgrifennu mewn cyd-destun amser arall neu wedi'i olygu ar gyfer rhywun arall.
+openpgp-sig-valid-unverified = Mae'r neges hon yn cynnwys llofnod digidol dilys o allwedd rydych chi eisoes wedi'i derbyn. Fodd bynnag, nid ydych wedi gwirio eto bod yr allwedd yn eiddo i'r anfonwr mewn gwirionedd.
+openpgp-sig-valid-verified = Mae'r neges hon yn cynnwys llofnod digidol dilys o allwedd wedi'i gwirio.
+openpgp-sig-valid-own-key = Mae'r neges hon yn cynnwys llofnod digidol dilys o'ch allwedd bersonol.
+# Variables:
+# $key (String) - The ID of the OpenPGP key used to create the signature.
+openpgp-sig-key-id = ID allwedd llofnodwr: { $key }
+# Variables:
+# $key (String) - The primary ID of the OpenPGP key used to create the signature.
+# $subkey (String) - A subkey of the primary key was used to create the signature, and this is the ID of that subkey.
+openpgp-sig-key-id-with-subkey-id = ID allwedd llofnodwr: { $key } (ID Is-allwedd: { $subkey })
+# Variables:
+# $key (String) - The ID of the user's OpenPGP key used to decrypt the message.
+openpgp-enc-key-id = ID eich allwedd dadgryptio: { $key }
+# Variables:
+# $key (String) - The primary ID of the user's OpenPGP key used to decrypt the message.
+# $subkey (String) - A subkey of the primary key was used to decrypt the message, and this is the ID of that subkey.
+openpgp-enc-key-with-subkey-id = ID eich allwedd dadgryptio: { $key } (ID Is-allwedd: { $subkey })
+openpgp-enc-none = Nid yw'r Neges wedi'i Hamgryptio
+openpgp-enc-none-label = Nid yw'r neges hon wedi'i hamgryptio cyn ei hanfon. Mae modd i eraill weld negeseuon sy'n cael eu hanfon ar draws y rhyngrwyd ac sydd heb eu hamgryptio.
+openpgp-enc-invalid-label = Nid Oes Modd Dadgryptio'r Neges
+openpgp-enc-invalid = Mae'r neges wedi'i hamgryptio cyn ei hanfon atoch, ond nid oes modd ei dadgryptio.
+openpgp-enc-clueless = Mae yna anawsterau anhysbys gyda'r neges wedi'i hamgryptio.
+openpgp-enc-valid-label = Mae'r Neges wedi'i Hamgryptio
+openpgp-enc-valid = Amgryptiwyd y neges hon cyn ei hanfon atoch. Mae amgryptio yn sicrhau mai dim ond y derbynwyr y bwriadwyd iddynt ddarllen y neges sy'n gallu.
+openpgp-unknown-key-id = Allwedd anhysbys
+openpgp-other-enc-additional-key-ids = Yn ogystal, amgryptiwyd y neges i berchnogion yr allweddi canlynol:
+openpgp-other-enc-all-key-ids = Amgryptiwyd y neges i berchnogion yr allweddi canlynol:
+openpgp-message-header-encrypted-ok-icon =
+    .alt = Dadgryptio yn llwyddiannus
+openpgp-message-header-encrypted-notok-icon =
+    .alt = Methodd y dadgriptio
+openpgp-message-header-signed-ok-icon =
+    .alt = Llofnod da
+# Mismatch icon is used for notok state as well
+openpgp-message-header-signed-mismatch-icon =
+    .alt = Llofnod gwael
+openpgp-message-header-signed-unknown-icon =
+    .alt = Statws llofnod anhysbys
+openpgp-message-header-signed-verified-icon =
+    .alt = Llofnod wedi'i wirio
+openpgp-message-header-signed-unverified-icon =
+    .alt = Llofnod heb ei wirio
diff --git a/thunderbird-l10n/cy/localization/cy/messenger/openpgp/oneRecipientStatus.ftl b/thunderbird-l10n/cy/localization/cy/messenger/openpgp/oneRecipientStatus.ftl
new file mode 100644
index 0000000000..80d1aa193f
--- /dev/null
+++ b/thunderbird-l10n/cy/localization/cy/messenger/openpgp/oneRecipientStatus.ftl
@@ -0,0 +1,61 @@
+# This Source Code Form is subject to the terms of the Mozilla Public
+# License, v. 2.0. If a copy of the MPL was not distributed with this
+# file, You can obtain one at http://mozilla.org/MPL/2.0/.
+
+openpgp-one-recipient-status-title =
+    .title = Diogelwch Negeseuon OpenPGP
+openpgp-one-recipient-status-status =
+    .label = Statws
+openpgp-one-recipient-status-key-id =
+    .label = ID Allwedd
+openpgp-one-recipient-status-created-date =
+    .label = Crëwyd
+openpgp-one-recipient-status-expires-date =
+    .label = Daw i Ben
+openpgp-one-recipient-status-open-details =
+    .label = Agor manylion a golygu derbyniad...
+openpgp-one-recipient-status-discover =
+    .label = Darganfod allwedd newydd neu wedi'i diweddaru
+openpgp-one-recipient-status-instruction1 = I anfon neges wedi'i hamgryptio o ben-i-ben at dderbynnydd, mae angen i chi gael gafael ar ei allwedd gyhoeddus OpenPGP a'i nodi fel y'i derbyniwyd.
+openpgp-one-recipient-status-instruction2 = I gael eu allwedd gyhoeddus, eu mewnforio o e-bost y maent wedi'i anfon atoch ac sy'n ei gynnwys. Fel arall, gallwch geisio darganfod eu allwedd gyhoeddus ar gyfeiriadur.
+openpgp-key-own = Derbyniwyd (allwedd bersonol)
+openpgp-key-secret-not-personal = Ddim yn ddefnyddiadwy
+openpgp-key-verified = Derbyniwyd (dilyswyd)
+openpgp-key-unverified = Derbyniwyd (heb ei wirio)
+openpgp-key-undecided = Heb ei dderbyn (heb benderfynu)
+openpgp-key-rejected = Heb ei dderbyn (gwrthodwyd)
+openpgp-key-expired = Daeth i Ben
+# Variables:
+# $key (String) - Recipient email address.
+openpgp-intro = Allweddi cyhoeddus sydd ar gael ar gyfer { $key }
+# Variables:
+# $kid (String) - Public key id to import.
+openpgp-pubkey-import-id = ID: { $kid }
+# Variables:
+# $fpr (String) - Fingerprint of the public key to import.
+openpgp-pubkey-import-fpr = Bysbrint: { $fpr }
+# Variables:
+# $num (Number) - Number of public keys contained in the key file.
+openpgp-pubkey-import-intro =
+    { $num ->
+        [zero] Nid yw'r ffeil yn cynnwys allweddi cyhoeddus
+        [one] Mae'r ffeil yn cynnwys un allwedd gyhoeddus fel sy'n cael ei ddangos isod:
+        [two] Mae'r ffeil yn cynnwys { $num } allwedd gyhoeddus fel sy'n cael ei ddangos isod:
+        [few] Mae'r ffeil yn cynnwys { $num } allwedd gyhoeddus fel sy'n cael ei ddangos isod:
+        [many] Mae'r ffeil yn cynnwys { $num } allwedd gyhoeddus fel sy'n cael ei ddangos isod:
+       *[other] Mae'r ffeil yn cynnwys { $num } allwedd gyhoeddus fel sy'n cael ei ddangos isod:
+    }
+# Variables:
+# $num (Number) - Number of keys to accept.
+openpgp-pubkey-import-accept =
+    { $num ->
+        [zero] Ydych chi'n derbyn yr allweddi hyn ar gyfer gwirio llofnodion digidol ac ar gyfer amgryptio negeseuon?
+        [one] Ydych chi'n derbyn yr allwedd hon ar gyfer gwirio llofnodion digidol ac ar gyfer amgryptio negeseuon?
+        [two] Ydych chi'n derbyn yr allweddi hyn ar gyfer gwirio llofnodion digidol ac ar gyfer amgryptio negeseuon?
+        [few] Ydych chi'n derbyn yr allweddi hyn ar gyfer gwirio llofnodion digidol ac ar gyfer amgryptio negeseuon?
+        [many] Ydych chi'n derbyn yr allweddi hyn ar gyfer gwirio llofnodion digidol ac ar gyfer amgryptio negeseuon?
+       *[other] Ydych chi'n derbyn yr allweddi hyn ar gyfer gwirio llofnodion digidol ac ar gyfer amgryptio negeseuon?
+    }
+pubkey-import-button =
+    .buttonlabelaccept = Mewnforio
+    .buttonaccesskeyaccept = M
diff --git a/thunderbird-l10n/cy/localization/cy/messenger/openpgp/openpgp-frontend.ftl b/thunderbird-l10n/cy/localization/cy/messenger/openpgp/openpgp-frontend.ftl
new file mode 100644
index 0000000000..45aba12430
--- /dev/null
+++ b/thunderbird-l10n/cy/localization/cy/messenger/openpgp/openpgp-frontend.ftl
@@ -0,0 +1,52 @@
+# This Source Code Form is subject to the terms of the Mozilla Public
+# License, v. 2.0. If a copy of the MPL was not distributed with this
+# file, You can obtain one at http://mozilla.org/MPL/2.0/.
+
+openpgp-manage-keys-openpgp-cmd =
+    .label = Rheolwr Allweddi OpenPGP
+    .accesskey = R
+openpgp-ctx-decrypt-open =
+    .label = Dadgryptio ac Agor
+    .accesskey = D
+openpgp-ctx-decrypt-save =
+    .label = Dadgryptio a Chadw Fel…
+    .accesskey = C
+openpgp-ctx-import-key =
+    .label = Mewnforio Allwedd OpenPGP
+    .accesskey = M
+openpgp-ctx-verify-att =
+    .label = Gwirio Llofnod
+    .accesskey = G
+openpgp-has-sender-key = Mae'r neges hon yn honni ei bod yn cynnwys allwedd gyhoeddus OpenPGP yr anfonwr.
+openpgp-be-careful-new-key = Rhybudd: Mae'r allwedd gyhoeddus OpenPGP newydd yn y neges hon yn wahanol i'r allweddi cyhoeddus y gwnaethoch eu derbyn o'r blaen gan { $email }
+openpgp-import-sender-key =
+    .label = Mewnforio…
+openpgp-search-keys-openpgp =
+    .label = Darganfod Allweddi OpenPGP
+openpgp-missing-signature-key = Llofnodwyd y neges hon ag allwedd nad yw gennych chi eto.
+openpgp-search-signature-key =
+    .label = Darganfod…
+# Don't translate the terms "OpenPGP" and "MS-Exchange"
+openpgp-broken-exchange-opened = Mae hon yn neges OpenPGP gafodd ei llygru yn ôl pob golwg gan MS-Exchange ac nid oes modd ei hatgyweirio oherwydd iddi gael ei hagor o ffeil leol. Copïwch y neges i mewn i ffolder e-bost i roi cynnig ar ei hatgyweirio'n awtomatig.
+openpgp-broken-exchange-info = Neges OpenPGP yw hon a gafodd ei llygru yn ôl pob golwg gan MS-Exchange. Os na yw cynnwys y neges yn cael ei ddangos yn ôl y disgwyl, gallwch roi cynnig ar atgyweiriad awtomatig.
+openpgp-broken-exchange-repair =
+    .label = Atgyweirio neges
+openpgp-broken-exchange-wait = Arhoswch…
+openpgp-has-nested-encrypted-parts = Mae'r neges hon yn cynnwys rhannau ychwanegol wedi'u hamgryptio.
+openpgp-show-encrypted-parts = Dadgryptio a Dangos
+openpgp-cannot-decrypt-because-mdc =
+    Neges wedi'i hamgryptio yw hon sy'n defnyddio hen fecanwaith bregus.
+    Gall fod wedi cael ei addasu wrth gael ei gludo, gyda'r bwriad o ddwyn ei gynnwys.
+    Er mwyn atal y risg hon, nid yw'r cynnwys yn cael ei ddangos.
+openpgp-cannot-decrypt-because-missing-key = Nid yw'r allwedd gyfrinachol sy'n ofynnol i ddadgryptio'r neges hon ar gael.
+openpgp-partially-signed =
+    Dim ond is-set o'r neges hon a lofnodwyd yn ddigidol gan ddefnyddio OpenPGP.
+    Os cliciwch y botwm gwirio, bydd y rhannau heb ddiogelwch yn cael eu cuddio, a bydd statws y llofnod digidol yn cael ei ddangos.
+openpgp-partially-encrypted =
+    Dim ond is-set o'r neges hon a amgryptiwyd gan ddefnyddio OpenPGP.
+    Nid yw rhannau darllenadwy o'r neges sy'n cael eu dangos eisoes wedi eu hamgryptio.
+    Os cliciwch y botwm dadgryptio, bydd cynnwys y rhannau wedi'u hamgryptio yn cael eu dangos.
+openpgp-reminder-partial-display = Nodyn i'ch atgoffa: Dim ond is-set o'r neges wreiddiol yw'r neges sy'n cael ei ddangos isod.
+openpgp-partial-verify-button = Gwirio
+openpgp-partial-decrypt-button = Dadgryptio
+openpgp-unexpected-key-for-you = Rhybudd: Mae'r neges hon yn cynnwys allwedd OpenPGP anhysbys sy'n cyfeirio at un o'ch cyfeiriadau e-bost chi eich hun. Os nad yw hwn yn un o'ch allweddi chi, gall fod yn ymgais i dwyllo gohebwyr eraill.
diff --git a/thunderbird-l10n/cy/localization/cy/messenger/openpgp/openpgp.ftl b/thunderbird-l10n/cy/localization/cy/messenger/openpgp/openpgp.ftl
new file mode 100644
index 0000000000..499eb9cbe6
--- /dev/null
+++ b/thunderbird-l10n/cy/localization/cy/messenger/openpgp/openpgp.ftl
@@ -0,0 +1,808 @@
+# This Source Code Form is subject to the terms of the Mozilla Public
+# License, v. 2.0. If a copy of the MPL was not distributed with this
+# file, You can obtain one at http://mozilla.org/MPL/2.0/.
+
+e2e-intro-description = I anfon negeseuon wedi'u hamgryptio neu wedi'u llofnodi'n ddigidol, mae angen i chi ffurfweddu technoleg amgryptio, naill ai OpenPGP neu S / MIME.
+e2e-intro-description-more = Dewiswch eich allwedd bersonol i alluogi defnyddio OpenPGP, neu'ch tystysgrif bersonol i alluogi defnyddio S/MIME. Ar gyfer allwedd neu dystysgrif bersonol chi sy'n berchen ar yr allwedd gyfrinachol gyfatebol.
+e2e-signing-description = Mae llofnod digidol yn caniatáu i dderbynwyr wirio bod y neges wedi'i hanfon gennych chi ac nad yw'r cynnwys wedi'i newid. Mae negeseuon amgryptiedig wedi eu llofnodi drwy ragosodiad.
+e2e-sign-message =
+    .label = Llofnodi negeseuon heb eu hamgryptio
+    .accesskey = h
+e2e-disable-enc =
+    .label = Analluogi amgryptio ar gyfer negeseuon newydd
+    .accesskey = A
+e2e-enable-enc =
+    .label = Galluogi amgryptio ar gyfer negeseuon newydd
+    .accesskey = G
+e2e-enable-description = Byddwch yn gallu analluogi amgryptio ar gyfer negeseuon unigol.
+e2e-advanced-section = Gosodiadau uwch
+e2e-attach-key =
+    .label = Atodwch fy allwedd gyhoeddus wrth ychwanegu llofnod digidol OpenPGP
+    .accesskey = A
+e2e-encrypt-subject =
+    .label = Amgryptio destun negeseuon OpenPGP
+    .accesskey = A
+e2e-encrypt-drafts =
+    .label = Cadw negeseuon drafft mewn fformat wedi'i amgryptio
+    .accesskey = C
+# Do not translate "Autocrypt", it's the name of a standard.
+e2e-autocrypt-headers =
+    .label = Anfonwch allwedd(i) cyhoeddus OpenPGP ym mhenawdau'r e-bost i sicrhau eu bod yn gydnaws ag Autocrypt
+    .accesskey = A
+openpgp-key-created-label =
+    .label = Crëwyd
+openpgp-key-expiry-label =
+    .label = Dod i ben
+openpgp-key-id-label =
+    .label = ID Allwedd
+openpgp-cannot-change-expiry = Mae hwn yn allwedd gyda strwythur cymhleth, nid yw newid ei ddyddiad dod i ben yn cael ei gefnogi.
+openpgp-key-man-title =
+    .title = Rheolwr Allweddi OpenPGP
+openpgp-key-man-dialog-title = Rheolwr Allweddi OpenPGP
+openpgp-key-man-generate =
+    .label = Pâr Allweddi Newydd
+    .accesskey = P
+openpgp-key-man-gen-revoke =
+    .label = Tystysgrif Dirymu
+    .accesskey = D
+openpgp-key-man-ctx-gen-revoke-label =
+    .label = Cynhyrchu a Chadw Tystysgrif Dirymu
+openpgp-key-man-file-menu =
+    .label = Ffeil
+    .accesskey = F
+openpgp-key-man-edit-menu =
+    .label = Golygu
+    .accesskey = G
+openpgp-key-man-view-menu =
+    .label = Gweld
+    .accesskey = G
+openpgp-key-man-generate-menu =
+    .label = Cynhyrchu
+    .accesskey = C
+openpgp-key-man-keyserver-menu =
+    .label = Gweinydd Allweddi
+    .accesskey = G
+openpgp-key-man-import-public-from-file =
+    .label = Mewnforio Allwedd(i) Cyhoeddus o'r Ffeil
+    .accesskey = M
+openpgp-key-man-import-secret-from-file =
+    .label = Mewnforio Allwedd(i) Cyfrinachol o'r Ffeil
+openpgp-key-man-import-sig-from-file =
+    .label = Mewnforio Dirymiad(au) o'r Ffeil
+openpgp-key-man-import-from-clipbrd =
+    .label = Mewnforio Allwedd(i) o'r Clipfwrdd
+    .accesskey = C
+openpgp-key-man-import-from-url =
+    .label = Mewnforio Allwedd(i) o URL
+    .accesskey = U
+openpgp-key-man-export-to-file =
+    .label = Allforio Allwedd(i) Cyhoeddus i Ffeil
+    .accesskey = F
+openpgp-key-man-send-keys =
+    .label = Anfon Allwedd(i) Cyhoeddus Trwy E-bost
+    .accesskey = E
+openpgp-key-man-backup-secret-keys =
+    .label = Allwedd(i) Cyfrinachol Wrth Gefn I'w Ffeilio
+    .accesskey = G
+openpgp-key-man-discover-cmd =
+    .label = Darganfod Allweddi Ar-lein
+    .accesskey = D
+openpgp-key-man-publish-cmd =
+    .label = Cyhoeddi
+    .accesskey = C
+openpgp-key-publish = Cyhoeddi
+openpgp-key-man-discover-prompt = I ddarganfod allweddi OpenPGP ar-lein, ar weinydd allweddi neu ddefnyddio protocol WKD, rhowch naill ai gyfeiriad e-bost neu ID allwedd.
+openpgp-key-man-discover-progress = Chwilio…
+# Variables:
+# $keyserver (String) - The address of a server that contains a directory of OpenPGP public keys
+openpgp-key-publish-ok = Allwedd gyhoeddus wedi'i hanfon i "{ $keyserver }".
+# Variables:
+# $keyserver (String) - The address of a server that contains a directory of OpenPGP public keys
+openpgp-key-publish-fail = Wedi methu ag anfon eich allwedd gyhoeddus i " { $keyserver } ".
+openpgp-key-copy-key =
+    .label = Copïo Allwedd Gyhoeddus
+    .accesskey = G
+openpgp-key-export-key =
+    .label = Allforio Allwedd Gyhoeddus i Ffeil
+    .accesskey = A
+openpgp-key-backup-key =
+    .label = Gwneud Copi wrth Gefn o Allwedd Gyfrinachol i Ffeil
+    .accesskey = G
+openpgp-key-send-key =
+    .label = Anfon Allwedd Gyhoeddus Trwy E-bost
+    .accesskey = A
+# Variables:
+# $count (Number) - Number of keys ids to copy.
+openpgp-key-man-copy-key-ids =
+    .label =
+        { $count ->
+            [zero] Copïo IDau Allwedd i'r Clipfwrdd
+            [one] Copïo ID Allwedd i'r Clipfwrdd
+            [two] Copïo ID Allwedd i'r Clipfwrdd
+            [few] Copïo ID Allwedd i'r Clipfwrdd
+            [many] Copïo ID Allwedd i'r Clipfwrdd
+           *[other] Copïo ID Allwedd i'r Clipfwrdd
+        }
+    .accesskey = I
+# Variables:
+# $count (Number) - Number of fingerprints to copy.
+openpgp-key-man-copy-fprs =
+    .label =
+        { $count ->
+            [zero] Copïo Bysbrintiau i'r Clipfwrdd
+            [one] Copïo Bysbrint i'r Clipfwrdd
+            [two] Copïo Bysbrint i'r Clipfwrdd
+            [few] Copïo Bysbrint i'r Clipfwrdd
+            [many] Copïo Bysbrint i'r Clipfwrdd
+           *[other] Copïo Bysbrint i'r Clipfwrdd
+        }
+    .accesskey = B
+# Variables:
+# $count (Number) - Number of public keys to copy.
+openpgp-key-man-copy-to-clipboard =
+    .label =
+        { $count ->
+            [zero] Copïo Allweddi Cyhoeddus I'r Clipfwrdd
+            [one] Copïo Allwedd Gyhoeddus I'r Clipfwrdd
+            [two] Copïo Allwedd Gyhoeddus I'r Clipfwrdd
+            [few] Copïo Allwedd Gyhoeddus I'r Clipfwrdd
+            [many] Copïo Allwedd Gyhoeddus I'r Clipfwrdd
+           *[other] Copïo Allwedd Gyhoeddus I'r Clipfwrdd
+        }
+    .accesskey = A
+openpgp-key-man-ctx-expor-to-file-label =
+    .label = Allforio Allweddi i Ffeil
+openpgp-key-man-ctx-copy =
+    .label = Copïo
+    .accesskey = C
+# Variables:
+# $count (Number) - Number of fingerprints.
+openpgp-key-man-ctx-copy-fprs =
+    .label =
+        { $count ->
+            [zero] Bysbrintiau
+            [one] Bysbrint
+            [two] Bysbrint
+            [few] Bysbrint
+            [many] Bysbrint
+           *[other] Bysbrint
+        }
+    .accesskey = B
+# Variables:
+# $count (Number) - Number of key ids.
+openpgp-key-man-ctx-copy-key-ids =
+    .label =
+        { $count ->
+            [zero] ID Allwedd
+            [one] ID Allwedd
+            [two] ID Allwedd
+            [few] ID Allwedd
+            [many] ID Allwedd
+           *[other] ID Allwedd
+        }
+    .accesskey = D
+# Variables:
+# $count (Number) - Number of public keys.
+openpgp-key-man-ctx-copy-public-keys =
+    .label =
+        { $count ->
+            [zero] Allweddi Cyhoeddus
+            [one] Allwedd Gyhoeddus
+            [two] Allwedd Gyhoeddus
+            [few] Allwedd Gyhoeddus
+            [many] Allwedd Gyhoeddus
+           *[other] Allwedd Gyhoeddus
+        }
+    .accesskey = y
+openpgp-key-man-close =
+    .label = Cau
+openpgp-key-man-reload =
+    .label = Ail-lwytho Storfa Allweddi
+    .accesskey = S
+openpgp-key-man-change-expiry =
+    .label = Newid Dyddiad Dod i Ben
+    .accesskey = N
+openpgp-key-man-refresh-online =
+    .label = Adnewyddu Ar-lein
+    .accesskey = d
+openpgp-key-man-ignored-ids =
+    .label = Cyfeiriadau e-bost
+openpgp-key-man-del-key =
+    .label = Dileu Allwedd(i)
+    .accesskey = D
+openpgp-delete-key =
+    .label = Dileu Allwedd
+    .accesskey = A
+openpgp-key-man-revoke-key =
+    .label = Dirymu Allwedd
+    .accesskey = i
+openpgp-key-man-key-props =
+    .label = Priodweddau Allweddi
+    .accesskey = P
+openpgp-key-man-key-more =
+    .label = Rhagor
+    .accesskey = R
+openpgp-key-man-view-photo =
+    .label = ID Llun
+    .accesskey = L
+openpgp-key-man-ctx-view-photo-label =
+    .label = Gweld ID Llun
+openpgp-key-man-show-invalid-keys =
+    .label = Dangos allweddi annilys
+    .accesskey = D
+openpgp-key-man-show-others-keys =
+    .label = Dangos Allweddi Gan Bobl Eraill
+    .accesskey = B
+openpgp-key-man-user-id-label =
+    .label = Enw
+openpgp-key-man-fingerprint-label =
+    .label = Bysbrint
+openpgp-key-man-select-all =
+    .label = Dewis Pob Allwedd
+    .accesskey = P
+openpgp-key-man-empty-tree-tooltip =
+    .label = Rhowch dermau chwilio yn y blwch uchod
+openpgp-key-man-nothing-found-tooltip =
+    .label = Nid oes unrhyw allweddi yn cyd-fynd â'ch chwilio
+openpgp-key-man-please-wait-tooltip =
+    .label = Arhoswch tra bod allweddi yn cael eu llwytho...
+openpgp-key-man-filter-label =
+    .placeholder = Chwilio am allweddi
+openpgp-key-man-select-all-key =
+    .key = P
+openpgp-key-man-key-details-key =
+    .key = I
+openpgp-ign-addr-intro = Rydych yn derbyn defnyddio'r allwedd hon ar gyfer y cyfeiriadau e-bost dethol canlynol:
+openpgp-key-details-doc-title = Priodweddau Allweddi
+openpgp-key-details-signatures-tab =
+    .label = Ardystiadau
+openpgp-key-details-structure-tab =
+    .label = Strwythur
+openpgp-key-details-uid-certified-col =
+    .label = ID Defnyddiwr / Ardystiedig gan
+openpgp-key-details-key-id-label = ID Allwedd
+openpgp-key-details-user-id3-label = Perchennog Honedig Allwedd
+openpgp-key-details-id-label =
+    .label = ID
+openpgp-key-details-key-type-label = Math
+openpgp-key-details-key-part-label =
+    .label = Rhan Allwedd
+openpgp-key-details-attr-ignored = Rhybudd: Efallai na fydd yr allwedd hon yn gweithio yn ôl y disgwyl, oherwydd bod rhai o'i phriodweddau'n anniogel ac y mae modd eu hanwybyddu.
+openpgp-key-details-attr-upgrade-sec = Dylech uwchraddio'r priodweddau anniogel.
+openpgp-key-details-attr-upgrade-pub = Dylech ofyn i berchennog yr allwedd hon i uwchraddio'r priodweddau anniogel.
+openpgp-key-details-upgrade-unsafe =
+    .label = Uwchraddio Priodweddau Anniogel
+    .accesskey = U
+openpgp-key-details-upgrade-ok = Uwchraddiwyd yr allwedd yn llwyddiannus. Dylech rannu'r allwedd gyhoeddus wedi'i huwchraddio gyda'ch gohebwyr.
+openpgp-key-details-algorithm-label =
+    .label = Algorithm
+openpgp-key-details-size-label =
+    .label = Maint
+openpgp-key-details-created-label =
+    .label = Crëwyd
+openpgp-key-details-created-header = Crëwyd
+openpgp-key-details-expiry-label =
+    .label = Dod i ben
+openpgp-key-details-expiry-header = Dod i ben
+openpgp-key-details-usage-label =
+    .label = Defnydd
+openpgp-key-details-fingerprint-label = Bysbrint
+openpgp-key-details-legend-secret-missing = Ar gyfer bysellau sydd wedi'u marcio â (!) nid yw'r fysell gyfrinachol ar gael.
+openpgp-key-details-sel-action =
+    .label = Dewis gweithred...
+    .accesskey = g
+openpgp-card-details-close-window-label =
+    .buttonlabelaccept = Cau
+openpgp-acceptance-label =
+    .label = Eich Derbyn
+openpgp-acceptance-rejected-label =
+    .label = Na, gwrthodwch yr allwedd hon.
+openpgp-acceptance-undecided-label =
+    .label = Ddim eto, efallai yn hwyrach.
+openpgp-acceptance-unverified-label =
+    .label = Iawn, ond nid wyf wedi gwirio mai hwn yw'r allwedd gywir.
+openpgp-acceptance-verified-label =
+    .label = Ydw, rydw i wedi gwirio yn bersonol bod gan yr allwedd hon yr bysbrint cywir.
+key-accept-personal =
+    Yn yr allwedd hon, mae gennych rhan gyhoeddus a rhan gyfrinachol. Gallwch ei defnyddio fel allwedd bersonol.
+    Os rhoddwyd yr allwedd hon i chi gan rywun arall, yna peidiwch â'i defnyddio fel allwedd bersonol.
+openpgp-personal-no-label =
+    .label = Na, peidio'i defnyddio fel fy allwedd bersonol.
+openpgp-personal-yes-label =
+    .label = Iawn, trin yr allwedd hon fel allwedd bersonol.
+openpgp-passphrase-protection =
+    .label = Diogelu Cyfrinymadrodd
+openpgp-passphrase-status-unprotected = Heb ei ddiogelu
+openpgp-passphrase-status-primary-password = Wedi'i ddiogelu gan Brif Gyfrinair { -brand-short-name }
+openpgp-passphrase-status-user-passphrase = Wedi'i ddiogelu gan gyfrinymadrodd
+openpgp-passphrase-instruction-unprotected = Gosod cyfrinymadrodd i ddiogelu yr allwedd hon
+openpgp-passphrase-instruction-primary-password = Fel arall, diogelwch yr allwedd hon gyda chyfrinymadrodd gwahanol
+openpgp-passphrase-instruction-user-passphrase = Datglowch yr allwedd hon i newid ei ddiogelwch.
+openpgp-passphrase-unlock = Datgloi
+openpgp-passphrase-unlocked = Datglowyd yr allwedd yn llwyddiannus.
+openpgp-remove-protection = Tynnu diogelwch cyfrinymadrodd
+openpgp-use-primary-password = Tynnu cyfrinymadrodd a'i ddiogelu gyda Phrif Gyfrinair
+openpgp-passphrase-new = Cyfrinymadrodd newydd
+openpgp-passphrase-new-repeat = Cadarnhewch y cyfrinymadrodd newydd
+openpgp-passphrase-set = Gosodwch y cyfrinymadrodd
+openpgp-passphrase-change = Newidiwch y cyfrinymadrodd
+openpgp-copy-cmd-label =
+    .label = Copïo
+
+## e2e encryption settings
+
+#   $identity (String) - the email address of the currently selected identity
+openpgp-description-no-key = Nid oes gan { -brand-short-name } allwedd OpenPGP personol ar gyfer <b>{ $identity }</b>
+#   $count (Number) - the number of configured keys associated with the current identity
+#   $identity (String) - the email address of the currently selected identity
+openpgp-description-has-keys =
+    { $count ->
+        [zero] Mae { -brand-short-name } wedi canfod { $count } allwedd OpenPGP personol sy'n gysylltiedig â <b>{ $identity }</b>
+        [one] Mae { -brand-short-name } wedi canfod { $count } allwedd OpenPGP personol sy'n gysylltiedig â <b>{ $identity }</b>
+        [two] Mae { -brand-short-name } wedi canfod { $count } allwedd OpenPGP personol sy'n gysylltiedig â <b>{ $identity }</b>
+        [few] Mae { -brand-short-name } wedi canfod { $count } allwedd OpenPGP personol sy'n gysylltiedig â <b>{ $identity }</b>
+        [many] Mae { -brand-short-name } wedi canfod { $count } allwedd OpenPGP personol sy'n gysylltiedig â <b>{ $identity }</b>
+       *[other] Mae { -brand-short-name } wedi canfod { $count } allwedd OpenPGP personol sy'n gysylltiedig â <b>{ $identity }</b>
+    }
+#   $key (String) - the currently selected OpenPGP key
+openpgp-selection-status-have-key = Mae eich ffurfweddiad cyfredol yn defnyddio ID allwedd <b>{ $key }</b>
+#   $key (String) - the currently selected OpenPGP key
+openpgp-selection-status-error = Mae eich ffurfweddiad cyfredol yn defnyddio ID allwedd <b>{ $key }</b>, sydd wedi dod i ben.
+openpgp-add-key-button =
+    .label = Ychwanegu Allwedd…
+    .accesskey = Y
+e2e-learn-more = Dysgu rhagor
+openpgp-keygen-success = Allwedd OpenPGP wedi'i chreu'n llwyddiannus!
+openpgp-keygen-import-success = Allweddi OpenPGP wedi'u mewnforio yn llwyddiannus!
+openpgp-keygen-external-success = ID Allwedd GnuPG Allanol wedi'i chadw!
+
+## OpenPGP Key selection area
+
+openpgp-radio-none =
+    .label = Dim
+openpgp-radio-none-desc = Peidiwch â defnyddio OpenPGP ar gyfer yr hunaniaeth hon.
+openpgp-radio-key-not-usable = Nid yw'r allwedd hon yn ddefnyddiadwy fel allwedd bersonol, oherwydd mae'r allwedd gyfrinachol ar goll!
+openpgp-radio-key-not-accepted = I ddefnyddio'r allwedd hon mae'n rhaid i chi ei chymeradwyo fel allwedd bersonol!
+openpgp-radio-key-not-found = Nid oedd modd canfod yr allwedd hon! Os ydych am ei defnyddio rhaid i chi ei mewnforio i { -brand-short-name }.
+#   $date (String) - the future expiration date of when the OpenPGP key will expire
+openpgp-radio-key-expires = Yn dod i ben ar: { $date }
+#   $date (String) - the past expiration date of when the OpenPGP key expired
+openpgp-radio-key-expired = Wedi dod i ben ar: { $date }
+openpgp-key-expires-within-6-months-icon =
+    .title = Mae'r allwedd yn dod i ben o fewn 6 mis
+openpgp-key-has-expired-icon =
+    .title = Daeth yr allwedd i ben
+openpgp-suggest-publishing-key = Mae cyhoeddi'r allwedd gyhoeddus ar weinydd allwedd yn caniatáu i eraill ei darganfod.
+openpgp-key-expand-section =
+    .tooltiptext = Rhagor o wybodaeth
+openpgp-key-revoke-title = Dirymu Allwedd
+openpgp-key-edit-title = Newid Allwedd OpenPGP
+openpgp-key-edit-date-title = Ymestyn Dyddiad Dod i Ben
+openpgp-manager-description = Defnyddiwch y Rheolwr Allweddi OpenPGP i weld a rheoli allweddi cyhoeddus eich gohebwyr a'r holl allweddi eraill nad ydynt wedi'u rhestru uchod.
+openpgp-manager-button =
+    .label = Rheolwr Allweddi OpenPGP
+    .accesskey = R
+openpgp-key-remove-external =
+    .label = Dileu ID Allwedd Allanol
+    .accesskey = D
+key-external-label = Allwedd GnuPG Allanol
+
+## Strings in keyDetailsDlg.xhtml
+
+key-type-public = allwedd gyhoeddus
+key-type-primary = allwedd gynradd
+key-type-subkey = is-allwedd
+key-type-pair = pâr o allweddi (allwedd gyfrinachol ac allwedd gyhoeddus)
+key-expiry-never = byth
+key-usage-encrypt = Amgryptio
+key-usage-sign = Llofnodi
+key-usage-certify = Tystio
+key-usage-authentication = Dilysu
+key-does-not-expire = Nid yw'r allwedd yn dod i ben
+# Variables:
+# $keyExpiry (String) - Date the key expired on.
+key-expired-date = Daeth yr allwedd i ben ar { $keyExpiry }
+key-expired-simple = Mae'r allwedd wedi dod i ben
+key-revoked-simple = Mae'r allwedd wedi'i dirymu
+key-do-you-accept = Ydych chi'n derbyn yr allwedd hon ar gyfer gwirio llofnodion digidol ac ar gyfer amgryptio negeseuon?
+# Variables:
+# $addr (String) - Email address the key claims it belongs to.
+key-verification = Dilyswch bysbrint yr allwedd gan ddefnyddio sianel gyfathrebu ddiogel ar wahân i e-bost i wneud yn siŵr mai dyma allwedd go iawn { $addr }.
+
+## Strings enigmailMsgComposeOverlay.js
+
+# Variables:
+# $problem (String) - Error message from key usability check.
+cannot-use-own-key-because = Methu anfon y neges, oherwydd mae problem gyda'ch allwedd bersonol. { $problem }
+window-locked = Mae'r ffenestr gyfansoddi wedi'i chloi; anfon wedi'i ddiddymu
+
+## Strings in keyserver.jsm
+
+keyserver-error-aborted = Ataliwyd
+keyserver-error-unknown = Digwyddodd gwall anhysbys
+keyserver-error-server-error = Adroddodd y gweinydd allweddi wall.
+keyserver-error-import-error = Wedi methu mewnforio'r allwedd wedi'i llwytho i lawr.
+keyserver-error-unavailable = Nid yw'r gweinydd allweddi ar gael.
+keyserver-error-security-error = Nid yw'r gweinydd allweddi'n cefnogi mynediad wedi'i amgryptio.
+keyserver-error-certificate-error = Nid yw tystysgrif y gweinydd allweddi'n ddilys.
+keyserver-error-unsupported = Nid yw'r gweinydd allweddi'n cael ei gynnal
+
+## Strings in mimeWkdHandler.jsm
+
+wkd-message-body-req =
+    Prosesodd eich darparwr e-bost eich cais i lwytho'ch allwedd gyhoeddus i fyny i Gyfeiriadur Allwedd Gwe OpenPGP.
+    Cadarnhewch i gwblhau cyhoeddi eich allwedd gyhoeddus.
+wkd-message-body-process =
+    E-bost yw hwn sy'n gysylltiedig â'r prosesu awtomatig i lwytho'ch allwedd gyhoeddus i fyny i Gyfeiriadur Allwedd Gwe OpenPGP.
+    Nid oes angen i chi gymryd unrhyw gamau â llaw ar hyn o bryd.
+
+## Strings in persistentCrypto.jsm
+
+# Variables:
+# $subject (String) - Subject of the message.
+converter-decrypt-body-failed =
+    Methu dadgryptio neges gyda'r pwnc
+    { $subject }.
+    Ydych chi am geisio eto gyda chyfrinair gwahanol neu a ydych chi am hepgor y neges?
+
+## Strings filters.jsm
+
+filter-folder-required = Rhaid dewis ffolder targed.
+filter-decrypt-move-warn-experimental =
+    Rhybudd - gall y weithred hidlo "Dadgryptio yn barhaol" arwain at negeseuon wedi'u dinistrio.
+    Rydym yn argymell yn gryf eich bod yn gyntaf yn rhoi cynnig ar yr hidlydd "Creu Copi wedi'i ddadgryptio", profi'r canlyniad yn ofalus, a dim ond ar ôl i chi fod yn fodlon â'r canlyniad yn dechrau defnyddio'r hidlydd.
+filter-term-pgpencrypted-label = Amgryptio OpenPGP
+filter-key-required = Rhaid dewis allwedd derbynnydd.
+# Variables:
+# $desc (String) - Email address to look for a key of.
+filter-key-not-found = Methu cnfod allwedd amgryptio ar gyfer '{ $desc }'.
+# Variables:
+# $desc (String) - The ID of a secret key that is required to read the email after the user executes the current action.
+filter-warn-key-not-secret =
+    Rhybudd - mae'r weithred hidlo "Amgryptio i allwedd" yn disodli'r derbynwyr.
+    Os nad oes gennych yr allwedd gyfrinachol ar gyfer '{ $desc }' fyddwch chi ddim yn gallu darllen yr e-byst bellach.
+
+## Strings filtersWrapper.jsm
+
+filter-decrypt-move-label = Dadgryptio yn barhaol (OpenPGP)
+filter-decrypt-copy-label = Creu Copi wedi'i ddadgryptio (OpenPGP)
+filter-encrypt-label = Amgryptio i allwedd (OpenPGP)
+
+## Strings in enigmailKeyImportInfo.js
+
+import-info-title =
+    .title = Llwyddiant! Allweddi wedi'u mewnforio
+import-info-bits = Didau
+import-info-created = Crëwyd
+import-info-fpr = Bysbrint
+import-info-details = Gweld Manylion a rheoli derbyniad allweddi
+import-info-no-keys = Dim allweddi wedi'u mewnforio.
+
+## Strings in enigmailKeyManager.js
+
+import-from-clip = Hoffech chi fewnforio rhywfaint o allweddi o'r clipfwrdd?
+import-from-url = Llwytho allwedd gyhoeddus i lawr o'r URL hwn:
+copy-to-clipbrd-failed = Methu copïo'r allweddi hyn i'r clipfwrdd.
+copy-to-clipbrd-ok = Copïwyd allweddi i'r clipfwrdd
+# Variables:
+# $userId (String) - User id of the key.
+delete-secret-key =
+    RHYBUDD: Rydych chi ar fin dileu allwedd gyfrinachol!
+    
+    Os byddwch yn dileu eich allwedd gyfrinachol, ni fydd modd i chi ddadgryptio unrhyw negeseuon sydd wedi'u hamgryptio ar gyfer yr allwedd honno bellach, ac ni fyddwch yn gallu ei dirymu.
+    
+    Ydych chi wir eisiau DILEU'R allwedd gyfrinachol a'r allwedd gyhoeddus
+    '{ $userId }'?
+delete-mix =
+    RHYBUDD: Rydych chi ar fin dileu allwedd gyfrinachol!
+    Os byddwch yn dileu eich allwedd gyfrinachol, ni fydd modd i chi ddadgryptio unrhyw negeseuon sydd wedi'u hamgryptio ar gyfer yr allwedd honno bellach.
+    Ydych chi wir eisiau DILEU'R allwedd gyfrinachol a'r un gyhoeddus?
+# Variables:
+# $userId (String) - User id of the key.
+delete-pub-key =
+    Ydych chi eisiau dileu'r allwedd gyhoeddus
+    '{ $userId }'?
+delete-selected-pub-key = Ydych chi eisiau dileu'r allwedd gyhoeddus'?
+refresh-all-question = Nid ydych wedi dewis unrhyw allwedd. Hoffech chi adnewyddu POB allwedd?
+key-man-button-export-sec-key = &Allforio Allweddi Cyfrinachol
+key-man-button-export-pub-key = Allforion Allweddi &Cyhoeddus yn Unig
+key-man-button-refresh-all = Adnewyddu &Pob Allwedd
+key-man-loading-keys = Llwytho allweddi, arhoswch...
+ascii-armor-file = Ffeiliau Arfogaeth ASCII (* .asc)
+no-key-selected = Dylech ddewis o leiaf un allwedd er mwyn cyflawni'r weithred hon
+export-to-file = Allforio Allwedd Gyhoeddus i Ffeil
+export-keypair-to-file = Allforio Allwedd Gyfrinachol a Chyhoeddus i Ffeil
+export-secret-key = Ydych chi am gynnwys yr allwedd gyfrinachol yn y ffeil allwedd OpenPGP sydd wedi'i chadw?
+save-keys-ok = Cadwyd yr allweddi'n llwyddiannus
+save-keys-failed = Methodd cadw'r allweddi
+default-pub-key-filename = Allweddi cyhoeddus wedi'u hallforio
+default-pub-sec-key-filename = Copi wrth gefn o allweddi cyfrinachol
+refresh-key-warn = Rhybudd: yn dibynnu ar nifer yr allweddi a chyflymder y cysylltiad, gall adnewyddu'r holl allweddi fod yn broses eithaf hir!
+preview-failed = Methu darllen ffeil allwedd gyhoeddus.
+# Variables:
+# $reason (String) - Error description.
+general-error = Gwall: { $reason }
+dlg-button-delete = &Dileu
+
+## Account settings export output
+
+openpgp-export-public-success = <b> Allforiwyd Allwedd Gyhoeddus yn llwyddiannus!</b>
+openpgp-export-public-fail = <b>Methu allforio'r allwedd gyhoeddus a ddewiswyd!</b>
+openpgp-export-secret-success = <b>Allforiwyd Allwedd Gyfrinachol yn llwyddiannus!</b>
+openpgp-export-secret-fail = <b>Methu allforio'r allwedd gyfrinachol a ddewiswyd!</b>
+
+## Strings in keyObj.jsm
+## Variables:
+## $userId (String) - The name and/or email address that is mentioned in the key's information.
+## $keyId (String) - Key id for the key entry.
+
+key-ring-pub-key-revoked = Mae'r allwedd { $userId } (ID allwedd { $keyId }) wedi'i dirymu.
+key-ring-pub-key-expired = Mae'r allwedd { $userId } (ID allwedd { $keyId }) wedi dod i ben.
+key-ring-no-secret-key = Nid yw'n ymddangos bod gennych yr allwedd gyfrinachol ar gyfer { $userId } (ID allwedd { $keyId }) ar eich cylch allweddi; nid oes modd i chi ddefnyddio'r allwedd ar gyfer llofnodi.
+key-ring-pub-key-not-for-signing = Nid oed modd defnyddio'r allwedd { $userId } (ID allweddl { $keyId } ar gyfer llofnodi.
+key-ring-pub-key-not-for-encryption = Nid oed modd defnyddio'r allwedd { $userId } (ID allweddl { $keyId } ar gyfer amgryptio.
+key-ring-sign-sub-keys-revoked = Mae'r holl is-allweddi lofnodi allwedd { $userId } (ID allweddl { $keyId }) yn cael eu dirymu.
+key-ring-sign-sub-keys-expired = Mae'r holl is-allweddi lofnodi allwedd { $userId } (ID allweddl { $keyId }) wedi dod i ben.
+key-ring-enc-sub-keys-revoked = Mae pob is-allwedd amgryptio allwedd { $userId } (ID allwedd { $keyId }) yn cael ei ddirymu.
+key-ring-enc-sub-keys-expired = Mae pob is-allwedd amgryptio allwedd { $userId } (ID allwedd { $keyId }) wedi dod i ben.
+
+## Strings in gnupg-keylist.jsm
+
+keyring-photo = Llun
+user-att-photo = Priodoledd defnyddiwr (delwedd JPEG)
+
+## Strings in key.jsm
+
+already-revoked = Mae'r allwedd hon eisoes wedi'i dirymu.
+#   $identity (String) - the id and associated user identity of the key being revoked
+revoke-key-question =
+    Rydych chi ar fin dirymu'r allwedd '{ $identity }'.
+    Ni fydd modd i chi llofnodi gyda'r allwedd hon mwyach, ac ar ôl ei dosbarthu, ni fydd eraill yn gallu amgryptio gyda'r allwedd honno mwyach. Gallwch barhau i ddefnyddio'r allwedd i ddadgryptio hen negeseuon.
+    Ydych chi am barhau?
+#   $keyId (String) - the id of the key being revoked
+revoke-key-not-present =
+    Nid oes gennych allwedd (0x { $keyId }) sy'n cyfateb i'r dystysgrif ddirymu hon!
+    Os ydych wedi colli'ch allwedd, rhaid i chi ei fewnforio (e.e. o weinydd allweddi) cyn mewnforio'r dystysgrif ddirymu!
+#   $keyId (String) - the id of the key being revoked
+revoke-key-already-revoked = Mae'r allwedd 0x { $keyId } eisoes wedi'i dirymu.
+key-man-button-revoke-key = &Dirymu Allwedd
+openpgp-key-revoke-success = Dirymwyd yr allwedd yn llwyddiannus.
+after-revoke-info =
+    Mae'r allwedd wedi'i dirymu.
+    Rhannwch yr allwedd gyhoeddus hon eto, trwy ei hanfon trwy e-bost, neu trwy ei llwytho i weinyddion allweddi, i adael i eraill wybod eich bod wedi dirymu'ch allwedd.
+    Cyn gynted ag y bydd y feddalwedd sy'n cael ei ddefnyddio gan bobl eraill yn gwybod am y dirymiad, bydd yn rhoi'r gorau i ddefnyddio'ch hen allwedd.
+    Os ydych chi'n defnyddio allwedd newydd ar gyfer yr un cyfeiriad e-bost, a'ch bod chi'n atodi'r allwedd gyhoeddus newydd i e-byst rydych chi'n eu hanfon, yna bydd gwybodaeth am eich hen allwedd wedi'i dirymu yn cael ei chynnwys yn awtomatig.
+
+## Strings in keyRing.jsm & decryption.jsm
+
+key-man-button-import = &Mewnforio
+delete-key-title = Dileu Allwedd OpenPGP
+delete-external-key-title = Tynnwch yr Allwedd GnuPG Allanol
+delete-external-key-description = Ydych chi am dynnu'r ID yr allwedd GnuPG Allanol hwn?
+key-in-use-title = Allwedd OpenPGP sy'n cael ei defnyddio ar hyn o bryd
+delete-key-in-use-description = Methu parhau! Mae'r allwedd rydych wedi'i dewis i'w dileu yn cael ei defnyddio ar hyn o bryd gan yr hunaniaeth hon. Dewiswch allwedd wahanol, neu dewiswch ddim, a cheisiwch eto.
+revoke-key-in-use-description = Methu parhau! Mae'r allwedd rydych wedi'i dewis i'w dileu yn cael ei defnyddio ar hyn o bryd gan yr hunaniaeth hon. Dewiswch allwedd wahanol, neu dewiswch ddim, a cheisiwch eto.
+
+## Strings used in errorHandling.jsm
+
+# Variables:
+# $keySpec (String) - Email address.
+key-error-key-spec-not-found = Nid oes modd cydweddu'r cyfeiriad e-bost '{ $keySpec }' ag allwedd ar eich cylch allweddi.
+# $keySpec (String) - Key id.
+key-error-key-id-not-found = Nid oes modd dod o hyd i ID yr allwedd wedi'i ffurfweddu '{ $keySpec }' ar eich cylch allweddi.
+# $keySpec (String) - Key id.
+key-error-not-accepted-as-personal = Nid ydych wedi cadarnhau mai'r allwedd gydag ID '{ $keySpec }' yw eich allwedd bersonol.
+
+## Strings used in enigmailKeyManager.js & windows.jsm
+
+need-online = Nid yw'r swyddogaeth rydych chi wedi'i dewis ar gael yn y modd all-lein. Ewch ar-lein a rhoi cynnig arall arni.
+
+## Strings used in keyRing.jsm & keyLookupHelper.jsm
+
+no-key-found2 = Nid oeddwn yn gallu canfod unrhyw allwedd sy'n cyfateb i'r meini prawf chwilio penodol yna.
+no-update-found = Mae gennych eisoes yr allweddi a ddarganfuwyd ar-lein.
+
+## Strings used in keyRing.jsm & GnuPGCryptoAPI.jsm
+
+fail-key-extract = Gwall - methodd y gorchymyn echdynnu allwedd
+
+## Strings used in keyRing.jsm
+
+fail-cancel = Gwall - Allwedd yn cael ei ddiddymu gan y defnyddiwr
+not-first-block = Gwall - Y bloc OpenPGP cyntaf nid bloc allwedd gyhoeddus
+import-key-confirm = Mewnforio allwedd(i) cyhoeddus wedi'u mewnblannu yn y neges?
+fail-key-import = Gwall - methodd mewnforio allweddi
+# Variables:
+# $output (String) - File that writing was attempted to.
+file-write-failed = Methwyd ysgrifennu at ffeil { $output }
+no-pgp-block = Gwall - Heb ddarganfod bloc data arfogaeth dilys OpenPGP
+confirm-permissive-import = Methodd y mewnforio. Efallai bod yr allwedd rydych chi'n ceisio ei fewnforio yn llygredig neu'n defnyddio priodoleddau anhysbys. Hoffech chi geisio mewnforio'r rhannau sy'n gywir? Gall hyn arwain at fewnforio allweddi anghyflawn ac nad oes modd eu defnyddio.
+
+## Strings used in trust.jsm
+
+key-valid-unknown = anhysbys
+key-valid-invalid = annilys
+key-valid-disabled = analluogwyd
+key-valid-revoked = dirymwyd
+key-valid-expired = daeth i ben
+key-trust-untrusted = di-ymddiried
+key-trust-marginal = ymylol
+key-trust-full = ymddiried ynddo
+key-trust-ultimate = eithaf
+key-trust-group = (grŵp)
+
+## Strings used in commonWorkflows.js
+
+import-key-file = Mewnforio Ffeil Allwedd OpenPGP
+import-rev-file = Mewnforio Ffeil Dirymu OpenPGP
+gnupg-file = Ffeiliau GnuPG
+import-keys-failed = Methodd mewnforio'r allweddi
+# Variables:
+# $key (String) - Key id to unlock.
+# $date (String) - The date on which the key was created
+# $username_and_email (String) - The user name, and/or the email address which the key owner has set for the key.
+passphrase-prompt2 = Rhowch y cyfrinymadrodd i ddatgloi'r allwedd gyfrinachol gyda'r ID { $key }, a grëwyd { $date } , { $username_and_email }
+# Variables:
+# $subkey (String) - Key id to unlock, which is a subkey.
+# $key (String) - This is the main key, to which the subkey belongs.
+# $date (String) - The date on which the key was created
+# $username_and_email (String) - The user name, and/or the email address which the key owner has set for the key.
+passphrase-prompt2-sub = Rhowch y cyfrinair i ddatgloi'r allwedd gyfrinachol gyda'r ID { $subkey } , sy'n isallwedd ID allwedd { $key }, a grëwyd { $date }, { $username_and_email }
+file-to-big-to-import = Mae'r ffeil hon yn rhy fawr. Peidiwch â mewnforio set fawr o allweddi ar unwaith.
+
+## Strings used in enigmailKeygen.js
+
+save-revoke-cert-as = Creu a Chadw Tystysgrif Dirymu
+revoke-cert-ok = Mae'r dystysgrif ddirymu wedi'i chreu'n llwyddiannus. Gallwch ei ddefnyddio i annilysu eich allwedd gyhoeddus, e.e. rhag ofn y byddwch yn colli'ch allwedd gyfrinachol.
+revoke-cert-failed = Nid oedd modd creu'r dystysgrif ddirymu.
+gen-going = Eisoes wrthi'n cynhyrchu allwedd!
+keygen-missing-user-name = Nid oes enw wedi'i nodi ar gyfer y cyfrif/hunaniaeth hon. Rhowch werth yn y maes   "Eich enw" yn yng ngosodiadau'r cyfrif.
+expiry-too-short = Rhaid i'ch allwedd fod yn ddilys am o leiaf un diwrnod.
+expiry-too-long = Nid oes modd i chi greu allwedd sy'n dod i ben mewn mwy na 100 mlynedd.
+# Variables:
+# $id (String) - Name and/or email address to generate keys for.
+key-confirm = Cynhyrchu allwedd gyhoeddus a chyfrinachol ar gyfer '{ $id }'?
+key-man-button-generate-key = &Cynhyrchu Allwedd
+key-abort = Atal cynhyrchu allwedd?
+key-man-button-generate-key-abort = &Atal Cynhyrchu Allwedd?
+key-man-button-generate-key-continue = &Parhau i Gynhyrchu Allweddi
+
+## Strings used in enigmailMessengerOverlay.js
+
+failed-decrypt = Gwall - methodd y dadgryptio
+fix-broken-exchange-msg-failed = Heb lwyddo i atgyweirio neges.
+# Variables:
+# $attachment (String) - File name of the signature file.
+attachment-no-match-from-signature = Methu cydweddu ffeil llofnod '{ $attachment }' ag atodiad
+# Variables:
+# $attachment (String) - File name of the attachment.
+attachment-no-match-to-signature = Methu cydweddu ffeil llofnod '{ $attachment }' â ffeil llofnod
+# Variables:
+# $attachment (String) - File name of the attachment
+signature-verified-ok = Gwiriwyd y llofnod ar gyfer atodiad { $attachment } yn llwyddiannus
+# Variables:
+# $attachment (String) - File name of the attachment
+signature-verify-failed = Methwyd gwirio y llofnod ar gyfer atodiad { $attachment }
+decrypt-ok-no-sig =
+    Rhybudd
+    Bu'r dadgryptio yn llwyddiant ond nid oedd modd gwirio'r llofnod yn iawn
+msg-ovl-button-cont-anyway = &Parhau Beth bynnag
+enig-content-note = *Nid yw atodiadau i'r neges hon wedi'u llofnodi na'u hamgryptio *
+
+## Strings used in enigmailMsgComposeOverlay.js
+
+msg-compose-button-send = &Anfon Neges
+msg-compose-details-button-label = Manylion…
+msg-compose-details-button-access-key = M
+send-aborted = Ataliwyd y weithred o anfon.
+# Variables:
+# $key (String) - Key id.
+key-not-trusted = Dim digon o ymddiriedaeth ar gyfer allwedd '{ $key }'
+# Variables:
+# $key (String) - Key id.
+key-not-found = Heb ddarganfod allwedd '{ $key }'
+# Variables:
+# $key (String) - Key id.
+key-revoked = Allwedd '{ $key }' wedi'i ddirymu
+# Variables:
+# $key (String) - Key id.
+key-expired = Allwedd '{ $key }' wedi dod i ben
+msg-compose-internal-error = Digwyddodd gwall mewnol.
+keys-to-export = Dewiswch Allweddi OpenPGP i'w Mewnosod
+msg-compose-partially-encrypted-inlinePGP =
+    Roedd y neges rydych chi'n ymateb iddi yn cynnwys rhannau heb eu hamgryptio ac wedi'u hamgryptio. Os nad oedd yr anfonwr yn gallu dadgryptio rhai rhannau o'r neges yn wreiddiol, efallai eich bod yn gollwng gwybodaeth gyfrinachol nad oedd yr anfonwr yn gallu dadgryptio ei hun yn wreiddiol.
+    Ystyriwch dynnu'r holl destun a ddyfynnwyd o'ch ateb i'r anfonwr hwn.
+msg-compose-cannot-save-draft = Gwall wrth gadw drafft
+msg-compose-partially-encrypted-short = Gwyliwch rhag gollwng gwybodaeth sensitif - e-bost wedi'i amgryptio'n rhannol.
+quoted-printable-warn =
+    Rydych wedi galluogi amgodio 'dyfyniad-argraffadwy' ar gyfer anfon negeseuon. Gall hyn arwain at ddadgryptio anghywir a/neu ddilysu'ch neges.
+    Ydych chi am ddiffodd anfon negeseuon 'dyfyniad-argraffadwy' nawr?
+# Variables:
+# $width (Number) - Number of characters per line.
+minimal-line-wrapping =
+    Rydych chi wedi gosod lapio llinell i nodau { $width }. Ar gyfer amgryptio a/neu lofnodi cywir, mae angen i'r gwerth hwn fod yn 68 o leiaf.
+    Ydych chi am newid amlapio llinell i 68 nod nawr?
+sending-news =
+    Ataliwyd gweithrediad anfon wedi'i amgryptio.
+    Nid oes modd amgryptio'r neges hon oherwydd bod derbynwyr grwpiau newyddion. Ail-anfonwch y neges heb amgryptio.
+send-to-news-warning =
+    Rhybudd: rydych chi ar fin anfon e-bost wedi'i amgryptio i grŵp newyddion.
+    Nid yw hyn yn cael ei annog oherwydd nad yw ond yn gwneud synnwyr os yw pob aelod o'r grŵp yn gallu dadgryptio'r neges, h.y. mae angen amgryptio'r neges gydag allweddi holl gyfranogwyr y grŵp. Anfonwch y neges hon dim ond os ydych chi'n gwybod yn union beth rydych chi'n ei wneud.
+    Parhau?
+save-attachment-header = Cadw atodiad wedi'i ddadgryptio
+possibly-pgp-mime = Neges wedi'i hamgryptio neu wedi'i llofnodi gan PGP/MIME o bosibl; defnyddiwch swyddogaeth 'Dadgryptio/Gwirio' i wirio
+# Variables:
+# $key (String) - Sender email address.
+cannot-send-sig-because-no-own-key = Methu llofnodi'r neges hon yn ddigidol, oherwydd nid ydych eto wedi ffurfweddu amgryptio pen-i-ben ar gyfer <{ $key }>
+# Variables:
+# $key (String) - Sender email address.
+cannot-send-enc-because-no-own-key = Methu anfon y neges hon wedi'i hamgryptio, oherwydd nid ydych eto wedi ffurfweddu amgryptio pen-i-ben ar gyfer <{ $key }>
+
+## Strings used in decryption.jsm
+
+# Variables:
+# $key (String) - Newline separated list of a tab character then name and/or email address mentioned in the key followed by the key id in parenthesis.
+do-import-multiple =
+    Mewnforio'r allweddi canlynol?
+    { $key }
+# Variables:
+# $name (String) - Name and/or email address mentioned in the key.
+# $id (String) - Key id of the key.
+do-import-one = Mewnforio { $name } ({ $id })?
+cant-import = Gwall wrth fewnforio allwedd gyhoeddus
+unverified-reply = Mae'n debyg bod rhan neges wedi'i mewnoli (ateb) wedi'i haddasu
+key-in-message-body = Wedi canfod allwedd yng nghorff y neges. Cliciwch 'Allwedd Mewnforio' i fewnforio'r allwedd
+sig-mismatch = Gwall - Camgydweddiad llofnod
+invalid-email = Gwall - cyfeiriad(au) e-bost annilys
+# Variables:
+# $name (String) - File name of the attachment.
+attachment-pgp-key =
+    Mae'n ymddangos bod yr atodiad '{ $name }' rydych chi'n ei agor yn ffeil allwedd OpenPGP.
+    Cliciwch 'Mewnforio' i fewnforio'r allweddi sydd wedi'u cynnwys neu 'Golwg' i weld cynnwys y ffeil mewn ffenestr porwr
+dlg-button-view = &Golwg
+
+## Strings used in enigmailMsgHdrViewOverlay.js
+
+decrypted-msg-with-format-error = Neges wedi'i dadgryptio (fformat e-bost PGP wedi'i dorri wedi'i adfer yn ôl pob tebyg wedi'i achosi gan hen weinydd Exchange, fel na fyddai'r canlyniad yn berffaith i'w darllen o bosibl)
+
+## Strings used in encryption.jsm
+
+not-required = Gwall - nid oes angen amgryptio
+
+## Strings used in windows.jsm
+
+no-photo-available = Dim Llun ar gael
+# Variables:
+# $photo (String) - Path of the photo in the key.
+error-photo-path-not-readable = Nid yw llwybr llun '{ $photo }' yn ddarllenadwy
+debug-log-title = Cofnod Dadfygio OpenPGP
+
+## Strings used in dialog.jsm
+
+# This string is followed by either repeat-suffix-singular if $count is 1 or else
+# by repeat-suffix-plural.
+# Variables:
+# $count (Number) - Number of times the alert will repeat.
+repeat-prefix = Bydd y rhybudd hwn yn ailadrodd { $count }
+repeat-suffix-singular = rhagor o amser.
+repeat-suffix-plural = rhagor o amser.
+no-repeat = Ni fydd y rhybudd hwn yn cael ei ddangos eto.
+dlg-keep-setting = Cofiwch fy ateb a pheidiwch â gofyn imi eto
+dlg-button-ok = &IAWN
+dlg-button-close = &Cau
+dlg-button-cancel = &Diddymu
+dlg-no-prompt = Peidio dangos y blwch deialog eto.
+enig-prompt = Anogwr OpenPGP
+enig-confirm = Cadarnhad OpenPGP
+enig-alert = Rhybudd OpenPGP
+enig-info = Manylion OpenPGP
+
+## Strings used in persistentCrypto.jsm
+
+dlg-button-retry = &Ceisio eto
+dlg-button-skip = &Hepgor
+
+## Strings used in enigmailMsgBox.js
+
+enig-alert-title =
+    .title = Rhybudd OpenPGP
diff --git a/thunderbird-l10n/cy/localization/cy/messenger/otr/add-finger.ftl b/thunderbird-l10n/cy/localization/cy/messenger/otr/add-finger.ftl
new file mode 100644
index 0000000000..0dac137db6
--- /dev/null
+++ b/thunderbird-l10n/cy/localization/cy/messenger/otr/add-finger.ftl
@@ -0,0 +1,16 @@
+# This Source Code Form is subject to the terms of the Mozilla Public
+# License, v. 2.0. If a copy of the MPL was not distributed with this
+# file, You can obtain one at http://mozilla.org/MPL/2.0/.
+
+otr-add-finger-title = Ychwanegu bysbrint Allwedd OTR
+
+# Variables:
+#   $name (String) - name of a chat contact person
+# Do not translate 'OTR' (name of an encryption protocol)
+otr-add-finger-description = Rhowch bysbrint allwedd OTR ar gyfer { $name }.
+
+otr-add-finger-fingerprint = Bysbrint
+otr-add-finger-tooltip-error = Nod annilys wedi'i roi. Dim ond llythrennau ABCDEF a rhifau sy'n cael eu caniatáu
+
+otr-add-finger-input =
+    .placeholder = Bysbrint allwedd OTR 40 nod o hyd
diff --git a/thunderbird-l10n/cy/localization/cy/messenger/otr/am-im-otr.ftl b/thunderbird-l10n/cy/localization/cy/messenger/otr/am-im-otr.ftl
new file mode 100644
index 0000000000..dbd8004669
--- /dev/null
+++ b/thunderbird-l10n/cy/localization/cy/messenger/otr/am-im-otr.ftl
@@ -0,0 +1,26 @@
+# This Source Code Form is subject to the terms of the Mozilla Public
+# License, v. 2.0. If a copy of the MPL was not distributed with this
+# file, You can obtain one at http://mozilla.org/MPL/2.0/.
+
+account-encryption =
+    .label = Amgryptio Pen-i-Ben
+account-otr-label = Negeseuon Dim Cofnod (OTR)
+account-otr-description2 = Mae { -brand-short-name } yn cefnogi amgryptio sgyrsiau un i un o'r dechrau i'r diwedd wedi ei seilio ar OTR. Mae hyn yn atal trydydd partïon rhag clustfeinio ar sgyrsiau. Dim ond pan fydd y person arall hefyd yn defnyddio meddalwedd sy'n cefnogi OTR y mae modd defnyddio amgryptio o'r dechrau i'r diwedd.
+otr-encryption-title = Amgryptio wedi'i Wirio
+otr-encryption-caption = Er mwyn galluogi pobl eraill i wirio'ch hunaniaeth mewn sgyrsiau OTR, rhannwch eich bysbrintiau OTR eich hun gan ddefnyddio sianel gyfathrebu allanol (tu-allan-i'r-band).
+otr-fingerprint-label = Eich Bysbrint:
+view-fingerprint-button =
+    .label = Rheoli Bysbrintiau Cysylltiadau
+    .accesskey = R
+otr-settings-title = Gosodiadau OTR
+otr-require-encryption =
+    .label = Angen amgryptio o'r dechrau i'r diwedd ar gyfer sgyrsiau un i un
+otr-require-encryption-info =
+    Wrth ofyn am amgryptio negeseuon o ben-i-ben, ni fydd negeseuon mewn sgyrsiau
+    un i un yn cael eu hanfon oni bai bod modd eu hamgryptio. Ni fydd negeseuon wedi'u
+    derbyn heb eu hamgryptio yn cael eu dangos fel rhan o'r sgwrs arferol, na'u cofnodi chwaith.
+otr-verify-nudge =
+    .label = Atgoffa bob tro i wirio cyswllt heb ei wirio
+
+otr-not-yet-available = ddim ar gael eto
+
diff --git a/thunderbird-l10n/cy/localization/cy/messenger/otr/auth.ftl b/thunderbird-l10n/cy/localization/cy/messenger/otr/auth.ftl
new file mode 100644
index 0000000000..da284a7bf6
--- /dev/null
+++ b/thunderbird-l10n/cy/localization/cy/messenger/otr/auth.ftl
@@ -0,0 +1,60 @@
+# This Source Code Form is subject to the terms of the Mozilla Public
+# License, v. 2.0. If a copy of the MPL was not distributed with this
+# file, You can obtain one at http://mozilla.org/MPL/2.0/.
+
+otr-auth =
+    .title = Gwirio hunaniaeth cyswllt
+    .buttonlabelaccept = Gwirio
+
+# Variables:
+#   $name (String) - the screen name of a chat contact person
+auth-title = Gwirio hunaniaeth { $name }
+
+# Variables:
+#   $own_name (String) - the user's own screen name
+auth-your-fp-value = Bysbrint i chi, { $own_name }:
+
+# Variables:
+#   $their_name (String) - the screen name of a chat contact
+auth-their-fp-value = Bysbrint i { $their_name }:
+
+auth-help = Mae gwirio hunaniaeth cyswllt yn helpu i sicrhau bod y sgwrs yn wirioneddol breifat, gan ei gwneud yn anodd iawn i drydydd parti glustfeinio neu drin y sgwrs.
+
+auth-help-title = Cymorth dilysu
+
+auth-question-received = Dyma'r cwestiwn sy'n cael ei ofyn gan eich cyswllt:
+
+auth-yes =
+    .label = Iawn
+
+auth-no =
+    .label = Na
+
+auth-verified = Rwyf wedi gwirio mai hwn yw'r bysprint cywir mewn gwirionedd.
+
+auth-manual-verification = Gwirio bysprintiau â llaw
+auth-question-and-answer = Cwestiwn ac ateb
+auth-shared-secret = Cyfrinach wedi'i rannu
+
+auth-manual-verification-label =
+    .label = { auth-manual-verification }
+
+auth-question-and-answer-label =
+    .label = { auth-question-and-answer }
+
+auth-shared-secret-label =
+    .label = { auth-shared-secret }
+
+auth-manual-instruction = Cysylltwch â'ch partner sgwrsio arfaethedig trwy ryw sianel ddilys arall, fel e-bost wedi'i lofnodi gan OpenPGP neu dros y ffôn. Fe ddylech ddweud wrth eich gilydd beth yw eich bysbrintiau.  (Mae bysbrintiau yn wiriad sy'n adnabod allwedd amgryptio.) Os yw'r bysprintiau yn cyfateb, dylech nodi yn y dialog isod eich bod wedi gwirio'r bysprint.
+
+auth-how = Sut hoffech chi wirio hunaniaeth eich cyswllt?
+
+auth-qa-instruction = Meddyliwch am gwestiwn y mae'r ateb yn hysbys i chi a'ch cyswllt yn unig. Rhowch y cwestiwn a'r ateb, yna arhoswch i'ch cyswllt roi'r ateb. Os nad yw'r atebion yn cydweddu, gall y sianel gyfathrebu rydych chi'n ei defnyddio fod o dan wyliadwriaeth.
+
+auth-secret-instruction = Meddyliwch am gyfrinach sy'n hysbys i chi a'ch cyswllt yn unig. Peidiwch â defnyddio'r un cysylltiad Rhyngrwyd i gyfnewid y gyfrinach. Rhowch y gyfrinach, yna arhoswch i'ch cyswllt ei roi. Os nad yw'r cyfrinachau yn cyfateb, gall y sianel gyfathrebu rydych chi'n ei defnyddio fod o dan wyliadwriaeth.
+
+auth-question = Rhowch gwestiwn:
+
+auth-answer = Rhowch yr ateb (sensitif i faint):
+
+auth-secret = Rhowch y gyfrinach:
diff --git a/thunderbird-l10n/cy/localization/cy/messenger/otr/chat.ftl b/thunderbird-l10n/cy/localization/cy/messenger/otr/chat.ftl
new file mode 100644
index 0000000000..8ca2af4cba
--- /dev/null
+++ b/thunderbird-l10n/cy/localization/cy/messenger/otr/chat.ftl
@@ -0,0 +1,19 @@
+# This Source Code Form is subject to the terms of the Mozilla Public
+# License, v. 2.0. If a copy of the MPL was not distributed with this
+# file, You can obtain one at http://mozilla.org/MPL/2.0/.
+
+state-label = Statws Amgryptio:
+
+start-text = Cychwynnwch sgwrs wedi'i hamgryptio
+
+start-label =
+    .label = { start-text }
+
+start-tooltip =
+    .tooltiptext = { start-text }
+
+end-label =
+    .label = Gorffennwch y sgwrs wedi'i hamgryptio
+
+auth-label =
+    .label = Gwiriwch hunaniaeth eich cyswllt
diff --git a/thunderbird-l10n/cy/localization/cy/messenger/otr/finger-sync.ftl b/thunderbird-l10n/cy/localization/cy/messenger/otr/finger-sync.ftl
new file mode 100644
index 0000000000..2b8b76e066
--- /dev/null
+++ b/thunderbird-l10n/cy/localization/cy/messenger/otr/finger-sync.ftl
@@ -0,0 +1,12 @@
+# This Source Code Form is subject to the terms of the Mozilla Public
+# License, v. 2.0. If a copy of the MPL was not distributed with this
+# file, You can obtain one at http://mozilla.org/MPL/2.0/.
+
+finger-yes = Gwiriwyd
+finger-no = Heb ei wirio
+
+finger-subset-title = Tynnu Bysbrintiau
+finger-subset-message = Nid oedd modd tynnu o leiaf un bysbrint, oherwydd ar hyn o bryd mae'r allwedd gyfatebol yn cael ei defnyddio mewn sgwrs weithredol.
+
+finger-remove-all-title = Tynnu'r Holl Bysbrintiau
+finger-remove-all-message = Ydych chi'n siŵr eich bod chi am dynnu'r holl bysbrintiau a welwyd o'r blaen? Bydd yr holl wiriadau hunaniaeth OTR blaenorol yn cael eu colli.
diff --git a/thunderbird-l10n/cy/localization/cy/messenger/otr/finger.ftl b/thunderbird-l10n/cy/localization/cy/messenger/otr/finger.ftl
new file mode 100644
index 0000000000..08df19fcec
--- /dev/null
+++ b/thunderbird-l10n/cy/localization/cy/messenger/otr/finger.ftl
@@ -0,0 +1,16 @@
+# This Source Code Form is subject to the terms of the Mozilla Public
+# License, v. 2.0. If a copy of the MPL was not distributed with this
+# file, You can obtain one at http://mozilla.org/MPL/2.0/.
+
+otr-finger-title = Bysbrintiau OTR a Welwyd Eisoes
+finger-intro = Bysprintiau allweddol OTR o sgyrsiau amgryptiedig blaenorol o'r pen-i-ben.
+finger-screen-name =
+    .label = Cysylltiad
+finger-verified =
+    .label = Statws Gwirio
+finger-fingerprint =
+    .label = Bysbrint
+finger-remove =
+    .label = Tynnu'r Dewis
+finger-remove-all =
+    .label = Tynnu'r Cyfan
diff --git a/thunderbird-l10n/cy/localization/cy/messenger/otr/otr.ftl b/thunderbird-l10n/cy/localization/cy/messenger/otr/otr.ftl
new file mode 100644
index 0000000000..98477eb96a
--- /dev/null
+++ b/thunderbird-l10n/cy/localization/cy/messenger/otr/otr.ftl
@@ -0,0 +1,97 @@
+# This Source Code Form is subject to the terms of the Mozilla Public
+# License, v. 2.0. If a copy of the MPL was not distributed with this
+# file, You can obtain one at http://mozilla.org/MPL/2.0/.
+
+# Variables:
+#   $name (String) - the screen name of a chat contact person
+msgevent-encryption-required-part1 = Fe wnaethoch geisio anfon neges heb ei hamgryptio at { $name }. O ran polisi, nid yw negeseuon heb eu hamgryptio'n cael eu caniatáu.
+
+msgevent-encryption-required-part2 = Yn ceisio cychwyn sgwrs breifat. Bydd eich neges yn cael ei ail anfon pan fydd y sgwrs breifat yn cychwyn.
+msgevent-encryption-error = Digwyddodd gwall wrth amgryptio'ch neges. Nid yw'r neges wedi'i hanfon.
+
+# Variables:
+#   $name (String) - the screen name of a chat contact person
+msgevent-connection-ended = Mae { $name } eisoes wedi cau eu cysylltiad wedi'i amgryptio â chi. Er mwyn osgoi eich bod yn anfon neges heb ei hamgryptio ar ddamwain, nid yw eich neges wedi ei hanfon. Gorffennwch eich sgwrs wedi'i hamgryptio, neu ail gychwynnwch hi.
+
+# Variables:
+#   $name (String) - the screen name of a chat contact person
+msgevent-setup-error = Digwyddodd gwall wrth drefnu sgwrs breifat gyda { $name }.
+
+# Do not translate 'OTR' (name of an encryption protocol)
+msgevent-msg-reflected = Rydych yn derbyn eich negeseuon OTR eich hun. Rydych naill ai'n ceisio siarad â chi'ch hun, neu mae rhywun yn adlewyrchu'ch negeseuon yn ôl atoch chi.
+
+# Variables:
+#   $name (String) - the screen name of a chat contact person
+msgevent-msg-resent = Cafodd y neges olaf at { $name } ei hail anfon.
+
+# Variables:
+#   $name (String) - the screen name of a chat contact person
+msgevent-rcvdmsg-not-private = Mae'r neges amgryptiedig a dderbyniwyd gan { $name } yn annarllenadwy, gan nad ydych yn cyfathrebu'n breifat ar hyn o bryd.
+
+# Variables:
+#   $name (String) - the screen name of a chat contact person
+msgevent-rcvdmsg-unreadable = Rydych wedi derbyn neges amgryptiedig annarllenadwy gan { $name }.
+
+# Variables:
+#   $name (String) - the screen name of a chat contact person
+msgevent-rcvdmsg-malformed = Rydych wdi derbyn neges ddata wedi'i hanffurfio gan { $name }.
+
+# A Heartbeat is a technical message used to keep a connection alive.
+# Variables:
+#   $name (String) - the screen name of a chat contact person
+msgevent-log-heartbeat-rcvd = Curiad calon wedi'i dderbyn gan { $name }.
+
+# A Heartbeat is a technical message used to keep a connection alive.
+# Variables:
+#   $name (String) - the screen name of a chat contact person
+msgevent-log-heartbeat-sent = Curiad calon wedi'i anfon at { $name }.
+
+# Do not translate 'OTR' (name of an encryption protocol)
+msgevent-rcvdmsg-general-err = Digwyddodd gwall annisgwyl wrth geisio diogelu'ch sgwrs gan ddefnyddio OTR.
+
+# Variables:
+#   $name (String) - the screen name of a chat contact person
+#   $msg (string) - the message that was received.
+msgevent-rcvdmsg-unencrypted = Nid yw'r neges ganlynol a dderbyniwyd gan { $name } wedi'i hamgryptio: { $msg }
+
+# Do not translate 'OTR' (name of an encryption protocol)
+# Variables:
+#   $name (String) - the screen name of a chat contact person
+msgevent-rcvdmsg-unrecognized = Rydych wedi derbyn neges OTR heb ei hadnabod gan { $name }.
+
+# Variables:
+#   $name (String) - the screen name of a chat contact person
+msgevent-rcvdmsg-for-other-instance = Mae { $name } wedi anfon neges a fwriadwyd ar gyfer sesiwn wahanol. Os ydych wedi mewngofnodi sawl gwaith, efallai y bydd sesiwn arall wedi derbyn y neges.
+
+# Variables:
+#   $name (String) - the screen name of a chat contact person
+context-gone-secure-private = Cychwynnodd sgwrs breifat gyda { $name }.
+
+# Variables:
+#   $name (String) - the screen name of a chat contact person
+context-gone-secure-unverified = Cychwynnodd sgwrs breifat heb ei gwirio gyda { $name }.
+
+# Variables:
+#   $name (String) - the screen name of a chat contact person
+context-still-secure = Adnewyddwyd y sgwrs wedi'i hamgryptio yn llwyddiannus gyda { $name }.
+
+error-enc = Digwyddodd gwall wrth amgryptio'r neges.
+
+# Variables:
+#   $name (String) - the screen name of a chat contact person
+error-not-priv = Rydych wedi anfon data wedi'i amgryptio at { $name }, nad oedd yn ei ddisgwyl.
+
+error-unreadable = Rydych wedi trosglwyddo neges annarllenadwy wedi'i hamgryptio.
+error-malformed = Rydych wedi trosglwyddo neges ddata wedi'i hanffurfio.
+
+resent = [ail anfon]
+
+# Variables:
+#   $name (String) - the screen name of a chat contact person
+tlv-disconnected = Mae { $name } wedi dod â'u sgwrs wedi'i hamgryptio gyda chi i ben; dylech wneud yr un peth.
+
+# Do not translate "Off-the-Record" and "OTR" which is the name of an encryption protocol
+# Make sure that this string does NOT contain any numbers, e.g. like "3".
+# Variables:
+#   $name (String) - the screen name of a chat contact person
+query-msg = Mae { $name } wedi gofyn am sgwrs di-gofnod wedi'i hamgryptio (OTR). Fodd bynnag, nid oes gennych ategyn i gefnogi hynny. Gweler https://en.wikipedia.org/wiki/Off-the-Record_Messaging i gael mwy o wybodaeth.
diff --git a/thunderbird-l10n/cy/localization/cy/messenger/otr/otrUI.ftl b/thunderbird-l10n/cy/localization/cy/messenger/otr/otrUI.ftl
new file mode 100644
index 0000000000..b9263ab8e0
--- /dev/null
+++ b/thunderbird-l10n/cy/localization/cy/messenger/otr/otrUI.ftl
@@ -0,0 +1,66 @@
+# This Source Code Form is subject to the terms of the Mozilla Public
+# License, v. 2.0. If a copy of the MPL was not distributed with this
+# file, You can obtain one at http://mozilla.org/MPL/2.0/.
+
+start-label = Cychwynnwch sgwrs wedi'i hamgryptio
+refresh-label = Adnewyddu sgwrs wedi'i hamgryptio
+auth-label = Gwiriwch hunaniaeth eich cyswllt
+reauth-label = Ail wirio hunaniaeth eich cyswllt
+auth-cancel = Diddymu
+auth-cancel-access-key = D
+auth-error = Digwyddodd gwall wrth wirio hunaniaeth eich cyswllt.
+auth-success = Gwirio hunaniaeth eich cyswllt wedi'i gwblhau'n llwyddiannus.
+auth-success-them = Mae eich cyswllt wedi gwirio'ch hunaniaeth yn llwyddiannus. Efallai yr hoffech chi wirio eu hunaniaeth hefyd trwy ofyn eich cwestiwn eich hun.
+auth-fail = Wedi methu gwirio hunaniaeth eich cyswllt.
+auth-waiting = Yn aros i'r cyswllt gwblhau'r gwiriad...
+finger-verify = Gwirio
+finger-verify-access-key = G
+finger-ignore = Anwybyddu
+finger-ignore-access-key = A
+# Do not translate 'OTR' (name of an encryption protocol)
+buddycontextmenu-label = Ychwanegu Bysbrint OTR
+# Variables:
+#   $name (String) - the screen name of a chat contact person
+alert-start = Yn ceisio cychwyn sgwrs wedi'i hamgryptio gyda { $name }.
+# Variables:
+#   $name (String) - the screen name of a chat contact person
+alert-refresh = Yn ceisio adnewyddu'r sgwrs wedi'i hamgryptio gyda { $name }.
+# Variables:
+#   $name (String) - the screen name of a chat contact person
+alert-gone-insecure = Daeth y sgwrs wedi'i hamgryptio gyda { $name } i ben.
+# Variables:
+#   $name (String) - the screen name of a chat contact person
+finger-unseen = Nid yw hunaniaeth { $name } wedi'i wirio eto. Nid yw'n bosibl i glustfeinio'n achlysurol, ond gyda pheth ymdrech gallai rhywun fod yn gwrando. Rhwystrwch  wyliadwriaeth trwy wirio hunaniaeth y cyswllt hwn.
+# Variables:
+#   $name (String) - the screen name of a chat contact person
+finger-seen = Mae { $name } yn cysylltu â chi o gyfrifiadur heb ei adnabod. Nid yw'n bosibl clustfeinio'n achlysurol, ond gyda pheth ymdrech gall rhywun fod yn gwrando. Rhwystrwch wyliadwriaeth trwy wirio hunaniaeth y cyswllt hwn.
+state-not-private = Nid yw'r sgwrs gyfredol yn breifat.
+state-generic-not-private = Nid yw'r sgwrs gyfredol yn breifat.
+# Variables:
+#   $name (String) - the screen name of a chat contact person
+state-unverified = Mae'r sgwrs gyfredol wedi'i hamgryptio ond nid yn breifat, gan nad yw hunaniaeth { $name } wedi'i gwirio eto.
+state-generic-unverified = Mae'r sgwrs gyfredol wedi'i hamgryptio ond nid yw'n breifat, gan nad yw rhai hunaniaethau wedi'u gwirio eto.
+# Variables:
+#   $name (String) - the screen name of a chat contact person
+state-private = Mae hunaniaeth { $name } wedi'i wirio. Mae'r sgwrs gyfredol wedi'i hamgryptio ac yn breifat.
+state-generic-private = Mae'r sgwrs gyfredol wedi'i hamgryptio ac yn breifat.
+# Variables:
+#   $name (String) - the screen name of a chat contact person
+state-finished = Mae { $name } wedi dod â'u sgwrs wedi'i hamgryptio gyda chi i ben; dylech wneud yr un peth.
+state-not-private-label = Anniogel
+state-unverified-label = Heb ei wirio
+state-private-label = Preifat
+state-finished-label = Wedi gorffen
+# Variables:
+#   $name (String) - the screen name of a chat contact person
+verify-request = Gofynnodd { $name } i gael dilysu'ch hunaniaeth.
+# Variables:
+#   $name (String) - the screen name of a chat contact person
+afterauth-private = Rydych wedi gwirio hunaniaeth { $name }.
+# Variables:
+#   $name (String) - the screen name of a chat contact person
+afterauth-unverified = Nid yw hunaniaeth { $name } wedi'i wirio.
+# Do not translate 'OTR' (name of an encryption protocol)
+# Variables:
+#   $error (String) - contains an error message that describes the cause of the failure
+otr-genkey-failed = Methodd cynhyrchu allwedd breifat OTR: { $error }
diff --git a/thunderbird-l10n/cy/localization/cy/messenger/policies/aboutPolicies.ftl b/thunderbird-l10n/cy/localization/cy/messenger/policies/aboutPolicies.ftl
new file mode 100644
index 0000000000..fb4f39bd49
--- /dev/null
+++ b/thunderbird-l10n/cy/localization/cy/messenger/policies/aboutPolicies.ftl
@@ -0,0 +1,17 @@
+# This Source Code Form is subject to the terms of the Mozilla Public
+# License, v. 2.0. If a copy of the MPL was not distributed with this
+# file, You can obtain one at http://mozilla.org/MPL/2.0/.
+
+about-policies-title = Polisïau Menter
+
+# 'Active' is used to describe the policies that are currently active
+active-policies-tab = Gweithredol
+errors-tab = Gwallau
+documentation-tab = Dogfennaeth
+
+no-specified-policies-message = Mae'r gwasanaeth Polisïau Menter yn weithredol ond nid oes unrhyw bolisïau wedi'u galluogi.
+inactive-message = Mae'r gwasanaeth Polisïau Menter yn anweithredol.
+
+policy-name = Enw'r Polisi
+policy-value = Gwerth Polisi
+policy-errors = Gwallau Polisi
diff --git a/thunderbird-l10n/cy/localization/cy/messenger/policies/policies-descriptions.ftl b/thunderbird-l10n/cy/localization/cy/messenger/policies/policies-descriptions.ftl
new file mode 100644
index 0000000000..fbae5f2a5e
--- /dev/null
+++ b/thunderbird-l10n/cy/localization/cy/messenger/policies/policies-descriptions.ftl
@@ -0,0 +1,159 @@
+# This Source Code Form is subject to the terms of the Mozilla Public
+# License, v. 2.0. If a copy of the MPL was not distributed with this
+# file, You can obtain one at http://mozilla.org/MPL/2.0/.
+
+
+## The Enterprise Policies feature is aimed at system administrators
+## who want to deploy these settings across several Thunderbird installations
+## all at once. This is traditionally done through the Windows Group Policy
+## feature, but the system also supports other forms of deployment.
+## These are short descriptions for individual policies, to be displayed
+## in the documentation section in about:policies.
+
+policy-3rdparty = Gosod polisïau y gall WebExtensions gael mynediad atyn nhw trwy chrome.storage.managed.
+
+policy-AppAutoUpdate = Galluogi neu analluogi diweddariad rhaglen awtomatig.
+
+policy-AppUpdatePin = Rhwystro { -brand-short-name } rhag cael ei ddiweddaru y tu hwnt i fersiwn penodedig.
+
+policy-AppUpdateURL = Gosod URL diweddaru ap cyfaddas.
+
+policy-Authentication = Ffurfweddu dilysu integredig ar gyfer gwefannau sy'n ei gefnogi.
+
+policy-BackgroundAppUpdate2 = Galluogi neu analluogi'r diweddarydd cefndir.
+
+policy-BlockAboutAddons = Rhwystro mynediad at y Rheolwr Ychwanegion (about:addons).
+
+policy-BlockAboutConfig = Rhwystro mynediad at dudalen about:config.
+
+policy-BlockAboutProfiles = Rhwystro mynediad at dudalen about:profiles.
+
+policy-BlockAboutSupport = Rhwystro mynediad at dudalen about:support.
+
+policy-CaptivePortal = Galluogi neu analluogi cefnogaeth porth caeth.
+
+policy-CertificatesDescription = Ychwanegu dystysgrifau neu ddefnyddio dystysgrifau mewnol.
+
+policy-Cookies = Caniatáu neu rwystro gwefannau rhag gosod cwcis.
+
+policy-DisableBuiltinPDFViewer = Analluogi PDF.js, y dangosydd PDF mewnol yn { -brand-short-name }.
+
+policy-DisabledCiphers = Analluogi seifferau.
+
+policy-DefaultDownloadDirectory = Gosod y cyfeiriadur llwytho i lawr rhagosodedig.
+
+policy-DisableAppUpdate = Rhwystro { -brand-short-name } rhag diweddaru.
+
+policy-DisableDefaultClientAgent = Atal asiant y cleient rhagosodedig rhag cymryd unrhyw gamau. Dim ond yn berthnasol i Windows; nid oes gan lwyfannau eraill yr asiant.
+
+policy-DisableDeveloperTools = Rhwystro mynediad at offer datblygwr.
+
+policy-DisableFeedbackCommands = Analluogi gorchmynion anfon adborth o'r ddewislen Cymorth (Cyflwyno Adborth ac Adrodd ar Wefan Dwyllodrus).
+
+policy-DisableForgetButton = Rhwystro mynediad at y botwm Anghofio.
+
+policy-DisableFormHistory = Peidio cofio chwilio a hanes ffurflenni.
+
+policy-DisableMasterPasswordCreation = Os true, nid oes modd creu prif gyfrinair.
+
+policy-DisablePasswordReveal = Peidio gadael i gyfrineiriau gael eu datgelu mewn mewngofnodion wedi'u cadw.
+
+policy-DisableProfileImport = Analluogi'r gorchymyn dewislen i Fewnforio data o raglen arall.
+
+policy-DisableSafeMode = Analluogi'r nodwedd i ailgychwyn yn y Modd Diogel. Sylw: dim ond drwy Bolisi Grŵp Windows y mae modd analluogi'r defnydd o fysell Shift i fynd i'r Modd Diogel.
+
+policy-DisableSecurityBypass = Rhwystro'r defnyddiwr rhag osgoi rhai rhybuddion diogelwch.
+
+policy-DisableSystemAddonUpdate = Rhwystro { -brand-short-name } rhag gosod a diweddaru ychwanegion y system.
+
+policy-DisableTelemetry = Diffodd Telemetreg.
+
+policy-DisplayMenuBar = Dangos y Bar Dewislen drwy ragosodiad.
+
+policy-DNSOverHTTPS = FFurfweddu DNS dros HTTPS
+
+policy-DontCheckDefaultClient = Analluogi gwirio am gleient rhagosodedig wrth gychwyn.
+
+policy-DownloadDirectory = Gosod a chloi'r cyfeiriadur llwytho i lawr.
+
+# “lock” means that the user won’t be able to change this setting
+policy-EnableTrackingProtection = Galluogi neu analluogi Rhwystro Cynnwys ac o ddewis ei gloi.
+
+# “lock” means that the user won’t be able to change this setting
+policy-EncryptedMediaExtensions = Galluogi neu analluogi Estyniadau Cyfryngau Amgryptiedig a'i gloi o ddewis.
+
+# A “locked” extension can’t be disabled or removed by the user. This policy
+# takes 3 keys (“Install”, ”Uninstall”, ”Locked”), you can either keep them in
+# English or translate them as verbs.
+policy-Extensions = Gosod, dadosod neu gloi estyniadau. Mae'r dewis gosod yn cymryd URL neu lwybrau fel paramedrau. Mae'r dewisiadau Dadosod a Chloi yn cymryd dynodiad estyniadau.
+
+policy-ExtensionSettings = Rheoli pob agwedd ar osod estyniad.
+
+policy-ExtensionUpdate = Galluogi neu analluogi diweddariadau awtomatig estyniad.
+
+policy-Handlers = Ffurfweddu trinwyr rhaglenni rhagosodedig.
+
+policy-HardwareAcceleration = Os false, diffoddwch gyflymder y caledwedd.
+
+policy-InstallAddonsPermission = Caniatáu i wefannau penodol osod ychwanegion.
+
+policy-LegacyProfiles = Analluoga'r nodwedd gan orfodi proffil ar wahân ar gyfer pob gosodiad.
+
+## Do not translate "SameSite", it's the name of a cookie attribute.
+
+policy-LegacySameSiteCookieBehaviorEnabled = Galluogi gosodiad ymddygiad rhagosodedig y cwci SameSite blaenorol.
+
+policy-LegacySameSiteCookieBehaviorEnabledForDomainList = Dychwelyd i'r ymddygiad SameSite blaenorol ar gyfer cwcis ar wefannau penodol.
+
+##
+
+policy-LocalFileLinks = Caniatáu i wefannau penodol gysylltu â ffeiliau lleol.
+
+policy-ManualAppUpdateOnly = Caniatáu diweddariadau â llaw yn unig a pheidio â hysbysu'r defnyddiwr am ddiweddariadau.
+
+policy-NetworkPrediction = Galluogi neu analluogi rhagfynegiad rhwydwaith (DNS prefetching).
+
+policy-OfferToSaveLogins = Gorfodi'r gosodiad i ganiatáu i { -brand-short-name } gynnig cofio mewngofnodion a chyfrineiriau wedi eu cadw. Mae gwerthoedd gwir a gau'n cael eu derbyn.
+
+policy-OfferToSaveLoginsDefault = Gosod y gwerth rhagosodedig ar gyfer caniatáu i { -brand-short-name } gynnig cofio mewngofnodion a chyfrineiriau wedi'u cadw. Mae gwerthoedd gwir a ffug yn cael eu derbyn.
+
+policy-OverrideFirstRunPage = Diystyru y dudalen rhediad gyntaf. Gosod y polisi hwn i gwag os ydych am analluogi'r dudalen rhediad cyntaf.
+
+policy-OverridePostUpdatePage = Diystyru'r dudalen ôl ddiweddaru "Beth sy'n Newydd". Gosodwch y polisi hwn i gwag os hoffech chi analluogi'r dudalen ôl ddiweddaru.
+
+policy-PasswordManagerEnabled = Galluogi cadw cyfrineiriau i'r rheolwr cyfrinair.
+
+# PDF.js and PDF should not be translated
+policy-PDFjs = Analluogi neu ffurfweddu PDF.js, darllenydd PDF mewnol { -brand-short-name }.
+
+policy-Permissions2 = Ffurfweddu caniatâd ar gyfer camera, meicroffon, lleoliad, hysbysiadau ac awtochwarae.
+
+policy-Preferences = Gosod a chloi'r gwerth ar gyfer is-set o ddewisiadau.
+
+policy-PrimaryPassword = Ei gwneud yn ofynnol neu i atal defnyddio Prif Gyfrinair.
+
+policy-PromptForDownloadLocation = Gofynnwch ble i arbed ffeiliau wrth eu llwytho i lawr.
+
+policy-Proxy = Ffurfweddi gosodiadau dirprwyol.
+
+policy-RequestedLocales = Gosod y rhestr o locales gofynnol ar gyfer y rhaglen yn ôl eich trefn dewis.
+
+policy-SanitizeOnShutdown2 = Clirio data llywio wrth gau.
+
+policy-SearchEngines = Ffurfweddu gosodiadau peiriannau chwilio. Dim ond yn y fersiwn Extended Support Release (ESR) mae'r polisi hwn ar gael.
+
+policy-SearchSuggestEnabled = Galluogi neu analluogi awgrymiadau chwilio.
+
+# For more information, see https://developer.mozilla.org/en-US/docs/Mozilla/Projects/NSS/PKCS11/Module_Installation
+policy-SecurityDevices = Gosod modiwlau PKCS#11.
+
+policy-SSLVersionMax = Gosod y fersiwn SSL uchaf.
+
+policy-SSLVersionMin = Gosodwch y fersiwn SSL leiaf.
+
+policy-SupportMenu = Ychwanegu eitem dewislen cymorth cyfaddas i'r ddewislen gymorth.
+
+policy-UserMessaging = Peidio dangos rhai negeseuon i'r defnyddiwr.
+
+# “format” refers to the format used for the value of this policy.
+policy-WebsiteFilter = Rhwystro gwefannau rhag derbyn ymweliadau. Gw. dogfennaeth am ragor o wybodaeth ar y fformat.
diff --git a/thunderbird-l10n/cy/localization/cy/messenger/preferences/am-copies.ftl b/thunderbird-l10n/cy/localization/cy/messenger/preferences/am-copies.ftl
new file mode 100644
index 0000000000..46d71416d4
--- /dev/null
+++ b/thunderbird-l10n/cy/localization/cy/messenger/preferences/am-copies.ftl
@@ -0,0 +1,5 @@
+# This Source Code Form is subject to the terms of the Mozilla Public
+# License, v. 2.0. If a copy of the MPL was not distributed with this
+# file, You can obtain one at http://mozilla.org/MPL/2.0/.
+
+account-prefs-show-address-row-description = Gadael y maes cyfeiriad yn wag bob tro i ddangos y rhes cyfeiriad wrth gychwyn neges newydd.
diff --git a/thunderbird-l10n/cy/localization/cy/messenger/preferences/am-im.ftl b/thunderbird-l10n/cy/localization/cy/messenger/preferences/am-im.ftl
new file mode 100644
index 0000000000..235a87a149
--- /dev/null
+++ b/thunderbird-l10n/cy/localization/cy/messenger/preferences/am-im.ftl
@@ -0,0 +1,23 @@
+# This Source Code Form is subject to the terms of the Mozilla Public
+# License, v. 2.0. If a copy of the MPL was not distributed with this
+# file, You can obtain one at http://mozilla.org/MPL/2.0/.
+
+account-settings-title = Gosodiadau Dilysu
+account-channel-title = Sianeli Rhagosodedig
+
+chat-autologin =
+    .label = Mewngofnodi wrth gychwyn
+
+chat-encryption-generic = Generig
+chat-encryption-log =
+    .label = Cynnwys negeseuon wedi'u hamgryptio o'r dechrau i'r diwedd mewn cofnodion sgwrsio
+chat-encryption-label = Amgryptio Cynhenid o'r Dechrau i'r Diwedd
+chat-encryption-description = Mae { $protocol } yn darparu amgryptio o'r dechrau i'r diwedd ar gyfer negeseuon sgwrsio. Mae hyn yn atal trydydd parti rhag clustfeinio ar sgyrsiau. Efallai y bydd angen camau gosod ychwanegol isod er mwyn i'r amgryptio fod yn weithredol.
+chat-encryption-status = Statws Amgryptio
+chat-encryption-placeholder = Amgryptio heb ei gychwyn.
+chat-encryption-sessions = Sesiynau
+chat-encryption-sessions-description = Er mwyn i amgryptio o'r dechrau i'r diwedd weithio'n gywir, mae'n rhaid i chi ymddiried yn y sesiynau eraill sydd wedi mewngofnodi i'ch cyfrif ar hyn o bryd. Mae angen rhyngweithio â'r rhaglen arall i wirio sesiwn. Gallai gwirio sesiwn arwain at bob sesiwn y mae'n ymddiried ynddo hefyd i gael eu hymddiried gan { -brand-short-name }.
+chat-encryption-session-verify = gwirio
+    .title = Gwirio hunaniaeth y sesiwn yma
+chat-encryption-session-trusted = ymddiried ynddo
+    .title = Mae hunaniaeth y sesiwn wedi'i wirio
diff --git a/thunderbird-l10n/cy/localization/cy/messenger/preferences/application-manager.ftl b/thunderbird-l10n/cy/localization/cy/messenger/preferences/application-manager.ftl
new file mode 100644
index 0000000000..6ba1857973
--- /dev/null
+++ b/thunderbird-l10n/cy/localization/cy/messenger/preferences/application-manager.ftl
@@ -0,0 +1,10 @@
+# This Source Code Form is subject to the terms of the Mozilla Public
+# License, v. 2.0. If a copy of the MPL was not distributed with this
+# file, You can obtain one at http://mozilla.org/MPL/2.0/.
+
+app-manager-window-dialog2 =
+    .title = Manylion Rhaglen
+app-manager-dialog-title = Manylion Rhaglen
+remove-app-button =
+    .label = Tynnu
+    .accesskey = T
diff --git a/thunderbird-l10n/cy/localization/cy/messenger/preferences/attachment-reminder.ftl b/thunderbird-l10n/cy/localization/cy/messenger/preferences/attachment-reminder.ftl
new file mode 100644
index 0000000000..3bb9f8796f
--- /dev/null
+++ b/thunderbird-l10n/cy/localization/cy/messenger/preferences/attachment-reminder.ftl
@@ -0,0 +1,21 @@
+# This Source Code Form is subject to the terms of the Mozilla Public
+# License, v. 2.0. If a copy of the MPL was not distributed with this
+# file, You can obtain one at http://mozilla.org/MPL/2.0/.
+
+attachment-reminder-window =
+    .title = Allweddair Atgoffa am Atodiad
+attachment-reminder-dialog-title = Allweddair Atgoffa am Atodiad
+attachment-reminder-label = Bydd { -brand-short-name } yn eich rhybuddio am atodiadau coll os ydych ar fin anfon e-bost yn cynnwys un o'r allweddeiriau hyn.
+keyword-new-button =
+    .label = Newydd…
+    .accesskey = N
+keyword-edit-button =
+    .label = Golygu…
+    .accesskey = G
+keyword-remove-button =
+    .label = Dileu
+    .accesskey = D
+new-keyword-title = Allweddair Newydd
+new-keyword-label = Allweddair:
+edit-keyword-title = Golygu Allweddair
+edit-keyword-label = Allweddair:
diff --git a/thunderbird-l10n/cy/localization/cy/messenger/preferences/colors.ftl b/thunderbird-l10n/cy/localization/cy/messenger/preferences/colors.ftl
new file mode 100644
index 0000000000..66f361075b
--- /dev/null
+++ b/thunderbird-l10n/cy/localization/cy/messenger/preferences/colors.ftl
@@ -0,0 +1,36 @@
+# This Source Code Form is subject to the terms of the Mozilla Public
+# License, v. 2.0. If a copy of the MPL was not distributed with this
+# file, You can obtain one at http://mozilla.org/MPL/2.0/.
+
+colors-dialog-window2 =
+    .title = Lliwiau
+colors-dialog-title = Lliwiau
+colors-dialog-legend = Testun a Chefndir
+text-color-label =
+    .value = Testun:
+    .accesskey = T
+background-color-label =
+    .value = Cefndir:
+    .accesskey = C
+use-system-colors =
+    .label = Defnyddio lliwiau'r system
+    .accesskey = s
+colors-link-legend = Lliw Dolenni
+link-color-label =
+    .value = Dolenni heb gael Ymweliad:
+    .accesskey = D
+visited-link-color-label =
+    .value = Dolenni wedi cael Ymweliad:
+    .accesskey = w
+underline-link-checkbox =
+    .label = Tanlinellu dolenni
+    .accesskey = d
+override-color-label =
+    .value = Anwybyddu'r lliwiau pennwyd gan y cynnwys gyda fy newis uchod:
+    .accesskey = A
+override-color-always =
+    .label = Bob tro
+override-color-auto =
+    .label = Dim ond gyda themâu Cyferbyniad Uchel
+override-color-never =
+    .label = Byth
diff --git a/thunderbird-l10n/cy/localization/cy/messenger/preferences/connection.ftl b/thunderbird-l10n/cy/localization/cy/messenger/preferences/connection.ftl
new file mode 100644
index 0000000000..9d1eb3fbb3
--- /dev/null
+++ b/thunderbird-l10n/cy/localization/cy/messenger/preferences/connection.ftl
@@ -0,0 +1,88 @@
+# This Source Code Form is subject to the terms of the Mozilla Public
+# License, v. 2.0. If a copy of the MPL was not distributed with this
+# file, You can obtain one at http://mozilla.org/MPL/2.0/.
+
+connection-dns-over-https-url-resolver = Defnyddio Darparwr
+    .accesskey = D
+# Variables:
+#   $name (String) - Display name or URL for the DNS over HTTPS provider
+connection-dns-over-https-url-item-default =
+    .label = { $name } (Rhagosodiad)
+    .tooltiptext = Defnyddiwch yr URL rhagosodedig ar gyfer datrys DNS dros HTTPS
+connection-dns-over-https-url-custom =
+    .label = Cyfaddas
+    .accesskey = C
+    .tooltiptext = Rhowch eich hoff URL er mwyn datrys DNS drod HTTPS
+connection-dns-over-https-custom-label = Cyfaddas
+connection-dialog-window2 =
+    .title = Gosodiadau Cysylltu
+connection-dialog-title = Gosodiadau Cysylltu
+disable-extension-button = Analluogi Estyniad
+# Variables:
+#   $name (String) - The extension that is controlling the proxy settings.
+#
+# The extension-icon is the extension's icon, or a fallback image. It should be
+# purely decoration for the actual extension name, with alt="".
+proxy-settings-controlled-by-extension = Mae estyniad, <img data-l10n-name="icon"/> { $name }, yn rheoli sut mae { -brand-short-name } yn cysylltu â'r Rhyngrwyd.
+connection-proxy-legend = Ffurfweddu'r Dirprwyon i Gael Mynediad i'r Rhyngrwyd
+proxy-type-no =
+    .label = Dim dirprwy
+    .accesskey = D
+proxy-type-wpad =
+    .label = Awtoganfod gosodiadau dirprwyol ar gyfer y rhwydwaith
+    .accesskey = w
+proxy-type-system =
+    .label = Defnyddio gosodiadau dirprwyol y system
+    .accesskey = e
+proxy-type-manual =
+    .label = Ffurfweddiad dirprwy gyda llaw:
+    .accesskey = F
+proxy-http-label =
+    .value = Dirprwy yr HTTP:
+    .accesskey = H
+http-port-label =
+    .value = Porth:
+    .accesskey = P
+proxy-http-sharing =
+    .label = Defnyddiwch y dirprwy yma hefyd ar gyfer HTTPS
+    .accesskey = D
+proxy-https-label =
+    .value = Dirprwy HTTPS:
+    .accesskey = S
+ssl-port-label =
+    .value = Porth:
+    .accesskey = o
+proxy-socks-label =
+    .value = Gwesteiwr SOCKS:
+    .accesskey = C
+socks-port-label =
+    .value = Porth:
+    .accesskey = t
+proxy-socks4-label =
+    .label = SOCKS v4
+    .accesskey = K
+proxy-socks5-label =
+    .label = SOCKS v5
+    .accesskey = v
+proxy-type-auto =
+    .label = URL ffurfweddu dirprwy yn awtomatig:
+    .accesskey = U
+proxy-reload-label =
+    .label = Ail-lwytho
+    .accesskey = l
+no-proxy-label =
+    .value = Dim Dirprwy ar gyfer:
+    .accesskey = m
+no-proxy-example = Esiampl: .mozilla.org, .net.nz, 192.168.1.0/24
+# Do not translate "localhost", "127.0.0.1/8" and "::1". (You can translate "and".)
+connection-proxy-noproxy-localhost-desc-2 = Nid yw cysylltiadau â localhost, 127.0.0.1/8, a ::1 byth yn cael eu dirprwyo.
+proxy-password-prompt =
+    .label = Peidio gofyn am ddilysiad os yw'r cyfrinair wedi ei gadw
+    .accesskey = d
+    .tooltiptext = Mae'r dewis hwn yn eich dilysu'n dawel i ddirprwyon rydych wedi eu cadw eu manylion ar eu cyfer. Byddwn yn gofyn os bydd y dilysiad yn methu.
+proxy-remote-dns =
+    .label = DNS dirprwyol pan y defnyddio SOCKS v5
+    .accesskey = D
+proxy-enable-doh =
+    .label = Galluogi DNS dros HTTPS
+    .accesskey = G
diff --git a/thunderbird-l10n/cy/localization/cy/messenger/preferences/cookies.ftl b/thunderbird-l10n/cy/localization/cy/messenger/preferences/cookies.ftl
new file mode 100644
index 0000000000..b377aaa332
--- /dev/null
+++ b/thunderbird-l10n/cy/localization/cy/messenger/preferences/cookies.ftl
@@ -0,0 +1,44 @@
+# This Source Code Form is subject to the terms of the Mozilla Public
+# License, v. 2.0. If a copy of the MPL was not distributed with this
+# file, You can obtain one at http://mozilla.org/MPL/2.0/.
+
+cookies-window-dialog2 =
+    .title = Cwcis
+cookies-dialog-title = Cwcis
+window-close-key =
+    .key = w
+window-focus-search-key =
+    .key = f
+window-focus-search-alt-key =
+    .key = k
+filter-search-label =
+    .value = Chwilio:
+    .accesskey = h
+cookies-on-system-label = Mae'r cwcis canlynol wedi'u cadw ar eich cyfrifiadur:
+treecol-site-header =
+    .label = Gwefan
+treecol-name-header =
+    .label = Enw'r Cwci
+props-name-label =
+    .value = Enw:
+props-value-label =
+    .value = Cynnwys:
+props-domain-label =
+    .value = Gwesteiwr:
+props-path-label =
+    .value = Llwybr:
+props-secure-label =
+    .value = Anfon am:
+props-expires-label =
+    .value = Daw i ben:
+props-container-label =
+    .value = Cynhwysydd:
+remove-cookie-button =
+    .label = Tynnu Cwci
+    .accesskey = T
+remove-all-cookies-button =
+    .label = Tynnu Pob Cwci
+    .accesskey = P
+cookie-close-button =
+    .label = Cau
+    .accesskey = u
diff --git a/thunderbird-l10n/cy/localization/cy/messenger/preferences/dock-options.ftl b/thunderbird-l10n/cy/localization/cy/messenger/preferences/dock-options.ftl
new file mode 100644
index 0000000000..8b4406abe3
--- /dev/null
+++ b/thunderbird-l10n/cy/localization/cy/messenger/preferences/dock-options.ftl
@@ -0,0 +1,23 @@
+# This Source Code Form is subject to the terms of the Mozilla Public
+# License, v. 2.0. If a copy of the MPL was not distributed with this
+# file, You can obtain one at http://mozilla.org/MPL/2.0/.
+
+dock-options-window-dialog2 =
+    .title = Dewisiadau eicon yr ap
+dock-options-dialog-title = Dewisiadau eicon yr ap
+dock-options-show-badge =
+    .label = Dangos eicon bathodyn
+    .accesskey = e
+bounce-system-dock-icon =
+    .label = Bywiogi eicon yr ap pan fydd neges newydd yn cyrraedd
+    .accesskey = B
+dock-icon-legend = Bathodyn eicon ap
+dock-icon-show-label =
+    .value = Bathodyn eicon ap gyda:
+count-unread-messages-radio =
+    .label = Cyfrif y negeseuon heb eu darllen
+    .accesskey = y
+count-new-messages-radio =
+    .label = Cyfrif y negeseuon newydd
+    .accesskey = y
+notification-settings-info2 = Gallwch analluogi'r bathodyn ym mhaen Hysbysiadau'r Dewisiadau System.
diff --git a/thunderbird-l10n/cy/localization/cy/messenger/preferences/fonts.ftl b/thunderbird-l10n/cy/localization/cy/messenger/preferences/fonts.ftl
new file mode 100644
index 0000000000..71fc55bc58
--- /dev/null
+++ b/thunderbird-l10n/cy/localization/cy/messenger/preferences/fonts.ftl
@@ -0,0 +1,134 @@
+# This Source Code Form is subject to the terms of the Mozilla Public
+# License, v. 2.0. If a copy of the MPL was not distributed with this
+# file, You can obtain one at http://mozilla.org/MPL/2.0/.
+
+fonts-dialog-title = Ffontiau
+fonts-window-close =
+    .key = w
+# Variables:
+#   $name {string, "Arial"} - Name of the default font
+fonts-label-default =
+    .label = Rhagosodiad ({ $name })
+fonts-label-default-unnamed =
+    .label = Rhagosodiad
+fonts-encoding-dialog-title =
+    .title = Ffontiau ac Amgodio
+fonts-language-legend =
+    .value = Ffontiau ar gyfer:
+    .accesskey = F
+fonts-proportional-label =
+    .value = Cyfrannol:
+    .accesskey = y
+
+## Languages
+
+# Note: Translate "Latin" as the name of Latin (Roman) script, not as the name of the Latin language.
+font-language-group-latin =
+    .label = Lladin
+font-language-group-japanese =
+    .label = Siapanëeg
+font-language-group-trad-chinese =
+    .label = Tsieinëeg Traddodiadol (Taiwan)
+font-language-group-simpl-chinese =
+    .label = Tsieinëeg Syml
+font-language-group-trad-chinese-hk =
+    .label = Tsieinëeg Traddodiadol (Hong Kong)
+font-language-group-korean =
+    .label = Corëeg
+font-language-group-cyrillic =
+    .label = Cyrilig
+font-language-group-el =
+    .label = Groeg
+font-language-group-other =
+    .label = Systemau Ysgrifennu Eraill
+font-language-group-thai =
+    .label = Thai
+font-language-group-hebrew =
+    .label = Hebraeg
+font-language-group-arabic =
+    .label = Arabeg
+font-language-group-devanagari =
+    .label = Devanagari
+font-language-group-tamil =
+    .label = Tamil
+font-language-group-armenian =
+    .label = Armeneg
+font-language-group-bengali =
+    .label = Bengali
+font-language-group-canadian =
+    .label = Sillafiad Unedig Canada
+font-language-group-ethiopic =
+    .label = Ethiopeg
+font-language-group-georgian =
+    .label = Georgeg
+font-language-group-gujarati =
+    .label = Gujarati
+font-language-group-gurmukhi =
+    .label = Gurmukhi
+font-language-group-khmer =
+    .label = Khmer
+font-language-group-malayalam =
+    .label = Malayalam
+font-language-group-math =
+    .label = Mathemateg
+font-language-group-odia =
+    .label = Odia
+font-language-group-telugu =
+    .label = Telugu
+font-language-group-kannada =
+    .label = Kannada
+font-language-group-sinhala =
+    .label = Sinhala
+font-language-group-tibetan =
+    .label = Tibeteg
+
+## Default font type
+
+default-font-serif =
+    .label = Serif
+default-font-sans-serif =
+    .label = Sans Serif
+font-size-proportional-label =
+    .value = Maint:
+    .accesskey = M
+font-size-monospace-label =
+    .value = Maint:
+    .accesskey = i
+font-serif-label =
+    .value = Serif:
+    .accesskey = S
+font-sans-serif-label =
+    .value = Sans-serif:
+    .accesskey = n
+font-monospace-label =
+    .value = Monospace:
+    .accesskey = M
+font-min-size-label =
+    .value = Lleiafswm maint ffont:
+    .accesskey = L
+min-size-none =
+    .label = Dim
+
+## Fonts in message
+
+font-control-legend = Rheoli Ffontiau
+use-document-fonts-checkbox =
+    .label = Caniatáu i negeseuon ddefnyddio ffontiau eraill
+    .accesskey = C
+use-fixed-width-plain-checkbox =
+    .label = Defnyddio ffont lled sefydlog ar gyfer negeseuon testun plaen
+    .accesskey = D
+
+## Language settings
+
+text-encoding-legend = Amgodiad Testun
+text-encoding-description = Gosod yr amgodiad testun rhagosodedig ar gyfer anfon a derbyn e-bost
+font-outgoing-email-label =
+    .value = Anfon E-bost:
+    .accesskey = A
+font-incoming-email-label =
+    .value = Derbyn E-bost:
+    .accesskey = D
+default-font-reply-checkbox =
+    .label = Pan yn bosib, defnyddio'r amgodiad testun rhagosodedig wrth ateb
+    .accesskey = a
diff --git a/thunderbird-l10n/cy/localization/cy/messenger/preferences/languages.ftl b/thunderbird-l10n/cy/localization/cy/messenger/preferences/languages.ftl
new file mode 100644
index 0000000000..7f4971a947
--- /dev/null
+++ b/thunderbird-l10n/cy/localization/cy/messenger/preferences/languages.ftl
@@ -0,0 +1,33 @@
+# This Source Code Form is subject to the terms of the Mozilla Public
+# License, v. 2.0. If a copy of the MPL was not distributed with this
+# file, You can obtain one at http://mozilla.org/MPL/2.0/.
+
+languages-customize-moveup =
+    .label = Symud i Fyny
+    .accesskey = F
+languages-customize-movedown =
+    .label = Symud i Lawr
+    .accesskey = L
+languages-customize-remove =
+    .label = Tynnu
+    .accesskey = T
+languages-customize-select-language =
+    .placeholder = Dewis iaith i'w hychwanegu…
+languages-customize-add =
+    .label = Ychwanegu
+    .accesskey = Y
+messenger-languages-window2 =
+    .title = Gosodiadau Iaith { -brand-short-name }
+messenger-languages-dialog-title = Gosodiadau Iaith { -brand-short-name }
+messenger-languages-description = Bydd { -brand-short-name } yn dangos yr iaith gyntaf fel eich rhagosodedig a bydd yn danogs ieithoedd eraill yn y drefn fyddan nhw'n ymddangos.
+messenger-languages-search = Chwilio am ragor o ieithoedd…
+messenger-languages-searching =
+    .label = Chwilio am ieithoedd…
+messenger-languages-downloading =
+    .label = Llwytho i lawr…
+messenger-languages-select-language =
+    .label = Dewis iaith i'w hychwanegu…
+    .placeholder = Dewis iaith i'w hychwanegu…
+messenger-languages-installed-label = Ieithoedd wedi'u gosod
+messenger-languages-available-label = Ieithoedd ar gael
+messenger-languages-error = Nid yw { -brand-short-name } yn gallu diweddaru eich iaith ar hyn o bryd. Edrychwch i weld os ydych wedi'ch cysylltu i'r rhyngrwyd neu ceisiwch eto.
diff --git a/thunderbird-l10n/cy/localization/cy/messenger/preferences/new-tag.ftl b/thunderbird-l10n/cy/localization/cy/messenger/preferences/new-tag.ftl
new file mode 100644
index 0000000000..b1c9acb5e2
--- /dev/null
+++ b/thunderbird-l10n/cy/localization/cy/messenger/preferences/new-tag.ftl
@@ -0,0 +1,13 @@
+# This Source Code Form is subject to the terms of the Mozilla Public
+# License, v. 2.0. If a copy of the MPL was not distributed with this
+# file, You can obtain one at http://mozilla.org/MPL/2.0/.
+
+tag-dialog-window =
+    .title = Tab Newydd
+tag-dialog-title = Tab Newydd
+tag-name-label =
+    .value = Enw Tag:
+    .accesskey = T
+tag-color-label =
+    .value = Lliw:
+    .accesskey = L
diff --git a/thunderbird-l10n/cy/localization/cy/messenger/preferences/notifications.ftl b/thunderbird-l10n/cy/localization/cy/messenger/preferences/notifications.ftl
new file mode 100644
index 0000000000..8c8f37069f
--- /dev/null
+++ b/thunderbird-l10n/cy/localization/cy/messenger/preferences/notifications.ftl
@@ -0,0 +1,29 @@
+# This Source Code Form is subject to the terms of the Mozilla Public
+# License, v. 2.0. If a copy of the MPL was not distributed with this
+# file, You can obtain one at http://mozilla.org/MPL/2.0/.
+
+notifications-dialog-window =
+    .title = Cyfaddasu Rhybudd E-bost Newydd
+notifications-dialog-title = Cyfaddasu Rhybudd E-bost Newydd
+customize-alert-description = Dewis pa faes i'w ddangos yn yr hysbysiad rhybudd:
+preview-text-checkbox =
+    .label = Testun Rhagolwg Neges
+    .accesskey = R
+subject-checkbox =
+    .label = Pwnc
+    .accesskey = P
+sender-checkbox =
+    .label = Anfonwr
+    .accesskey = A
+
+## Note: open-time-label-before is displayed first, then there's a field where
+## the user can enter a number, and open-time-label-after is displayed at the end
+## of the line. The translations of the open-time-label-before and open-time-label-after
+## parts don't have to mean the exact same thing as in English; please try instead
+## to translate the whole sentence.
+
+open-time-label-before =
+    .value = Dangos Rhybudd E-bost Newydd pob
+    .accesskey = N
+open-time-label-after =
+    .value = eiliad
diff --git a/thunderbird-l10n/cy/localization/cy/messenger/preferences/offline.ftl b/thunderbird-l10n/cy/localization/cy/messenger/preferences/offline.ftl
new file mode 100644
index 0000000000..512852150b
--- /dev/null
+++ b/thunderbird-l10n/cy/localization/cy/messenger/preferences/offline.ftl
@@ -0,0 +1,43 @@
+# This Source Code Form is subject to the terms of the Mozilla Public
+# License, v. 2.0. If a copy of the MPL was not distributed with this
+# file, You can obtain one at http://mozilla.org/MPL/2.0/.
+
+offline-dialog-window =
+    .title = Gosodiadau All-lein
+offline-dialog-title = Gosodiadau All-lein
+autodetect-online-label =
+    .label = Dilyn y cyflwr ar-lein canfuwyd, yn awtomatig
+    .accesskey = c
+offline-preference-startup-label = Cyflwr â llaw wrth gychwyn:
+status-radio-remember =
+    .label = Cofio'r cyflwr ar-lein diwethaf
+    .accesskey = o
+status-radio-ask =
+    .label = Gofyn i mi am y cyflwr ar-lein
+    .accesskey = G
+status-radio-always-online =
+    .label = Ar-lein
+    .accesskey = r
+status-radio-always-offline =
+    .label = All-lein
+    .accesskey = l
+going-online-label = Anfon negeseuon sydd heb eu hanfon wrth fynd ar-lein?
+going-online-auto =
+    .label = Iawn
+    .accesskey = I
+going-online-not =
+    .label = Na
+    .accesskey = N
+going-online-ask =
+    .label = Gofyn i mi
+    .accesskey = G
+going-offline-label = Llwytho negeseuon i lawr ar gyfer defnydd all-lein wrth fynd all-lein?
+going-offline-auto =
+    .label = Iawn
+    .accesskey = w
+going-offline-not =
+    .label = Na
+    .accesskey = a
+going-offline-ask =
+    .label = Gofyn i mi
+    .accesskey = f
diff --git a/thunderbird-l10n/cy/localization/cy/messenger/preferences/passwordManager.ftl b/thunderbird-l10n/cy/localization/cy/messenger/preferences/passwordManager.ftl
new file mode 100644
index 0000000000..55d1b44142
--- /dev/null
+++ b/thunderbird-l10n/cy/localization/cy/messenger/preferences/passwordManager.ftl
@@ -0,0 +1,83 @@
+# This Source Code Form is subject to the terms of the Mozilla Public
+# License, v. 2.0. If a copy of the MPL was not distributed with this
+# file, You can obtain one at http://mozilla.org/MPL/2.0/.
+
+saved-logins =
+    .title = Mewngofnodion wedi eu Cadw
+saved-logins-title = Mewngofnodion wedi eu Cadw
+window-close =
+    .key = c
+focus-search-primary-shortcut =
+    .key = c
+focus-search-alt-shortcut =
+    .key = c
+copy-provider-url-cmd =
+    .label = Copïo'r URL
+    .accesskey = U
+copy-username-cmd =
+    .label = Copïo Enw Defnyddiwr
+    .accesskey = E
+edit-username-cmd =
+    .label = Golygu Enw Defnyddiwr
+    .accesskey = G
+copy-password-cmd =
+    .label = Copïo'r Cyfrinair
+    .accesskey = o
+edit-password-cmd =
+    .label = Golygu'r Cyfrinair
+    .accesskey = G
+search-filter =
+    .accesskey = C
+    .placeholder = Chwilio
+column-heading-provider =
+    .label = Darparwr
+column-heading-username =
+    .label = Enw Defnyddiwr
+column-heading-password =
+    .label = Cyfrinair
+column-heading-time-created =
+    .label = Defnyddiwyd Gyntaf
+column-heading-time-last-used =
+    .label = Defnyddiwyd Diwethaf
+column-heading-time-password-changed =
+    .label = Newidiwyd Diwethaf
+column-heading-times-used =
+    .label = Nifer o Weithiau Defnyddiwyd
+remove =
+    .label = Tynnu
+    .accesskey = T
+import =
+    .label = Mewnforio…
+    .accesskey = M
+password-close-button =
+    .label = Cau
+    .accesskey = C
+show-passwords =
+    .label = Dangos Cyfrineiriau
+    .accesskey = D
+hide-passwords =
+    .label = Cuddio Cyfrineiriau
+    .accesskey = d
+logins-description-all = Mae mewngofnodion ar gyfer y darparwyr canlynol yn cael eu storio ar eich cyfrifiadur
+logins-description-filtered = Mae'r mewngofnodi canlynol yn cyd-fynd â'ch chwilio:
+remove-all =
+    .label = Tynnu'r Cyfan
+    .accesskey = T
+remove-all-shown =
+    .label = Tynnu'r Cyfan Dangoswyd
+    .accesskey = D
+remove-all-passwords-prompt = Ydych chi'n siŵr eich bod am dynnu pob cyfrinair?
+remove-all-passwords-title = Tynnu pob cyfrinair
+no-master-password-prompt = Ydych chi'n siŵr eich bod am ddangos eich cyfrineiriau?
+
+## OS Authentication dialog
+
+# This message can be seen by trying to show or copy the passwords.
+password-os-auth-dialog-message = Gwiriwch eich hunaniaeth i ddatgelu'r cyfrineiriau sydd wedi'u cadw.
+# This message can be seen by trying to show or copy the passwords.
+# The macOS strings are preceded by the operating system with "Thunderbird is trying to "
+# and includes subtitle of "Enter password for the user "xxx" to allow this." These
+# notes are only valid for English. Please test in your locale.
+password-os-auth-dialog-message-macosx = datgelu'r cyfrineiriau sydd wedi'u cadw
+# Don't change this label.
+password-os-auth-dialog-caption = { -brand-full-name }
diff --git a/thunderbird-l10n/cy/localization/cy/messenger/preferences/permissions.ftl b/thunderbird-l10n/cy/localization/cy/messenger/preferences/permissions.ftl
new file mode 100644
index 0000000000..4ce6ff8a9c
--- /dev/null
+++ b/thunderbird-l10n/cy/localization/cy/messenger/preferences/permissions.ftl
@@ -0,0 +1,43 @@
+# This Source Code Form is subject to the terms of the Mozilla Public
+# License, v. 2.0. If a copy of the MPL was not distributed with this
+# file, You can obtain one at http://mozilla.org/MPL/2.0/.
+
+permissions-reminder-window2 =
+    .title = Eithriadau
+permissions-dialog-title = Eithriadau
+permission-preferences-close-window =
+    .key = f
+website-address-label =
+    .value = Cyfeiriad y wefan:
+    .accesskey = w
+block-button =
+    .label = Rhwystro
+    .accesskey = R
+allow-session-button =
+    .label = Caniatáu ar gyfer y Sesiwn
+    .accesskey = S
+allow-button =
+    .label = Caniatáu
+    .accesskey = a
+treehead-sitename-label =
+    .label = Gwefan
+treehead-status-label =
+    .label = Statws
+remove-site-button =
+    .label = Tynnu'r Wefan
+    .accesskey = T
+remove-all-site-button =
+    .label = Tynnu Pob Gwefan
+    .accesskey = P
+cancel-button =
+    .label = Diddymu
+    .accesskey = D
+save-button =
+    .label = Cadw Newidiadau
+    .accesskey = N
+permission-can-label = Caniatáu
+permission-can-access-first-party-label = Caniatáu'r parti cyntaf yn unig
+permission-can-session-label = Caniatáu ar gyfer y Sesiwn
+permission-cannot-label = Rhwystro
+invalid-uri-message = Rhowch gyfeiriad e-bost dilys
+invalid-uri-title = Rhoddwyd Enw Parth Annilys
diff --git a/thunderbird-l10n/cy/localization/cy/messenger/preferences/preferences.ftl b/thunderbird-l10n/cy/localization/cy/messenger/preferences/preferences.ftl
new file mode 100644
index 0000000000..ebfc1b9568
--- /dev/null
+++ b/thunderbird-l10n/cy/localization/cy/messenger/preferences/preferences.ftl
@@ -0,0 +1,785 @@
+# This Source Code Form is subject to the terms of the Mozilla Public
+# License, v. 2.0. If a copy of the MPL was not distributed with this
+# file, You can obtain one at http://mozilla.org/MPL/2.0/.
+
+close-button =
+    .aria-label = Cau
+preferences-doc-title2 = Gosodiadau
+category-list =
+    .aria-label = Categorïau
+pane-general-title = Cyffredinol
+category-general =
+    .tooltiptext = { pane-general-title }
+pane-compose-title = Ysgrifennu
+category-compose =
+    .tooltiptext = Ysgrifennu
+pane-privacy-title = Preifatrwydd a Diogelwch
+category-privacy =
+    .tooltiptext = Preifatrwydd a Diogelwch
+pane-chat-title = Sgwrsio
+category-chat =
+    .tooltiptext = Sgwrsio
+pane-calendar-title = Calendr
+category-calendar =
+    .tooltiptext = Calendr
+pane-sync-title = Cydweddu
+category-sync =
+    .tooltiptext = Cydweddu
+general-language-and-appearance-header = Iaith a Gwedd
+general-incoming-mail-header = Derbyn E-byst
+general-files-and-attachment-header = Ffeiliau ac Atodiadau
+general-tags-header = Tagiau
+general-reading-and-display-header = Darllen a Dangos
+general-updates-header = Diweddariadau
+general-network-and-diskspace-header = Rhwydwaith a Lle ar Ddisg
+general-indexing-label = Mynegeio
+composition-category-header = Ysgrifennu
+composition-attachments-header = Atodiadau
+composition-spelling-title = Sillafu
+compose-html-style-title = Arddull HTML
+composition-addressing-header = Cyfeirio
+privacy-main-header = Preifatrwydd
+privacy-passwords-header = Cyfrineiriau
+privacy-junk-header = Sbam
+collection-header = Casglu a Defnyddio Data { -brand-short-name }
+collection-description = Rydym yn ceisio darparu dewisiadau i chi a chasglu dim ond beth sydd ei angen arnom i ddarparu a gwella { -brand-short-name } ar gyfer pawb. Rydym yn gofyn caniatâd bob tro cyn derbyn manylion personol.
+collection-privacy-notice = Hysbysiad Preifatrwydd
+collection-health-report-telemetry-disabled = Nid ydych bellach yn caniatáu i { -vendor-short-name } ddal data technegol a rhyngweithiol. Bydd holl ddata'r gorffennol yn cael ei ddileu cyn pen 30 diwrnod.
+collection-health-report-telemetry-disabled-link = Dysgu rhagor
+collection-health-report =
+    .label = Caniatáu i { -brand-short-name } anfon data technegol a rhyngweithio i { -vendor-short-name }
+    .accesskey = C
+collection-health-report-link = Dysgu rhagor
+# This message is displayed above disabled data sharing options in developer builds
+# or builds with no Telemetry support available.
+collection-health-report-disabled = Mae adrodd ar ddata wedi ei analluogi ar gyfer ffurfweddiad yr adeiledd hwn
+collection-backlogged-crash-reports =
+    .label = Caniatáu i { -brand-short-name } i anfon adroddiadau chwalu wedi eu cadw ar eich rhan
+    .accesskey = f
+collection-backlogged-crash-reports-link = Dysgu rhagor
+privacy-security-header = Diogelwch
+privacy-scam-detection-title = Canfod Twyll
+privacy-anti-virus-title = Gwrth Firws
+privacy-certificates-title = Tystysgrifau
+chat-pane-header = Sgwrsio
+chat-status-title = Statws
+chat-notifications-title = Hysbysiadau
+chat-pane-styling-header = Steilio
+choose-messenger-language-description = Dewis yr ieithoedd sy'n cael ei defnyddio i ddangos dewislenni, negeseuon, a hysbysiadau gan { -brand-short-name }
+manage-messenger-languages-button =
+    .label = Gosod Rhai Eraill...
+    .accesskey = G
+confirm-messenger-language-change-description = Ailgychwyn { -brand-short-name } i osod y newidiadau hyn
+confirm-messenger-language-change-button = Gosod ac Ailgychwyn
+update-setting-write-failure-title = Gwall wrth gadw dewisiadau Diweddaru
+# Variables:
+#   $path (String) - Path to the configuration file
+# The newlines between the main text and the line containing the path is
+# intentional so the path is easier to identify.
+update-setting-write-failure-message =
+    Bu gwall ar { -brand-short-name } ac nid yw wedi cadw'r newid hwn. Noder bod gosod caniatâd ar gyfer y diweddariad hwn yn gofyn am ganiatâd i ysgrifennu at y ffeil isod. Efallai y byddwch chi neu weinyddwr system yn gallu datrys y gwall trwy roi rheolaeth lawn i'r ffeil hon i'r grŵp Defnyddwyr.
+    
+    Doedd dim modd ysgrifennu i ffeil: { $path }
+update-in-progress-title = Diweddariad ar y Gweill
+update-in-progress-message = Ydych chi eisiau i { -brand-short-name } barhau gyda'r diweddariad hwn?
+update-in-progress-ok-button = &Dileu
+# Continue is the cancel button so pressing escape or using a platform standard
+# method of closing the UI will not discard the update.
+update-in-progress-cancel-button = &Parhau
+account-button = Gosodiadau Cyfrif
+open-addons-sidebar-button = Ychwanegion a Themâu
+
+## OS Authentication dialog
+
+# This message can be seen by trying to add a Primary Password.
+primary-password-os-auth-dialog-message-win = I greu Prif Gyfrinair, nodwch fanylion eich mewngofnodi Windows. Mae hyn yn helpu i ddiogelu eich cyfrifon.
+# This message can be seen by trying to add a Primary Password.
+# The macOS strings are preceded by the operating system with "Thunderbird is trying to "
+# and includes subtitle of "Enter password for the user "xxx" to allow this." These
+# notes are only valid for English. Please test in your locale.
+primary-password-os-auth-dialog-message-macosx = creu Prif Gyfrinair
+# Don't change this label.
+master-password-os-auth-dialog-caption = { -brand-full-name }
+
+## General Tab
+
+focus-search-shortcut =
+    .key = f
+focus-search-shortcut-alt =
+    .key = k
+general-legend = Tudalen Cychwyn { -brand-short-name }
+start-page-label =
+    .label = Pan fydd { -brand-short-name } yn cychwyn, dangos y Dudalen Cychwyn yn y maes neges
+    .accesskey = P
+location-label =
+    .value = Lleoliad:
+    .accesskey = o
+restore-default-label =
+    .label = Adfer y Rhagosodiad
+    .accesskey = R
+default-search-engine = Peiriant Chwilio Rhagosodedig
+add-web-search-engine =
+    .label = Ychwanegu…
+    .accesskey = Y
+remove-search-engine =
+    .label = Tynnu
+    .accesskey = T
+add-opensearch-provider-title = Ychwanegu Darparwr OpenSearch
+add-opensearch-provider-text = Rhowch URL y darparwr OpenSearch i'w ychwanegu. Naill ai defnyddiwch URL uniongyrchol y ffeil OpenSearch Description, neu URL lle mae modd ei ddarganfod yn awtomatig.
+adding-opensearch-provider-failed-title = Methodd Ychwanegu Darparwr OpenSearch
+# Variables:
+# $url (String) - URL an OpenSearch provider was requested for.
+adding-opensearch-provider-failed-text = Nid oedd modd ychwanegu OpenSearch Provider ar gyfer { $url }.
+minimize-to-tray-label =
+    .label = Pan fydd { -brand-short-name } wedi ei leihau, ei symud i'r dror
+    .accesskey = l
+new-message-arrival = Pan fydd neges newydd yn cyrraedd:
+mail-play-sound-label =
+    .label =
+        { PLATFORM() ->
+            [macos] Chwarae'r ffeil sain ganlynol:
+           *[other] Canu nodyn
+        }
+    .accesskey =
+        { PLATFORM() ->
+            [macos] C
+           *[other] n
+        }
+mail-play-button =
+    .label = Chwarae
+    .accesskey = h
+change-dock-icon = Newid dewisiadau eicon yr ap
+app-icon-options =
+    .label = Dewisiadau Eicon Ap…
+    .accesskey = E
+notification-settings2 = Mae modd analluogi rhybuddion a'r sain rhagosodedig ar baen Hysbysu'r Dewisiadau System.
+animated-alert-label =
+    .label = Dangos rhybudd
+    .accesskey = D
+customize-alert-label =
+    .label = Cyfaddasu…
+    .accesskey = C
+biff-use-system-alert =
+    .label = Defnyddio hysbysiadau'r system
+tray-icon-unread-label =
+    .label = Dangos eicon hambwrdd ar gyfer negeseuon heb eu darllen
+    .accesskey = h
+tray-icon-unread-description = Argymhellir wrth ddefnyddio botymau bar tasgau bach
+mail-system-sound-label =
+    .label = Sain rhagosodedig y system ar gyfer e-bost newydd
+    .accesskey = S
+mail-custom-sound-label =
+    .label = Defnyddio'r ffeil sain ganlynol
+    .accesskey = D
+mail-browse-sound-button =
+    .label = Pori…
+    .accesskey = P
+enable-gloda-search-label =
+    .label = Galluogi Chwilio a Mynegeio Eang
+    .accesskey = G
+datetime-formatting-legend = Fformatio Dyddiad ac Amser
+language-selector-legend = Iaith
+allow-hw-accel =
+    .label = Defnyddio cyflymu caledwedd pan fydd ar gael
+    .accesskey = y
+store-type-label =
+    .value = Math o Storio Negeseuon ar gyfer cyfrifon newydd:
+    .accesskey = M
+mbox-store-label =
+    .label = Ffeil i'r ffolder (mbox)
+maildir-store-label =
+    .label = Ffeil y neges (maildir)
+scrolling-legend = Sgrolio
+autoscroll-label =
+    .label = Defnyddio awto sgrolio
+    .accesskey = a
+smooth-scrolling-label =
+    .label = Defnyddio sgrolio llyfn
+    .accesskey = l
+browsing-gtk-use-non-overlay-scrollbars =
+    .label = Dango bariau sgrolio bob tro
+    .accesskey = D
+window-layout-legend = Cynllun Ffenestr
+draw-in-titlebar-label =
+    .label = Cuddio bar teitl ffenestr y system
+    .accesskey = C
+auto-hide-tabbar-label =
+    .label = Awtoguddio bar y tab
+    .accesskey = A
+auto-hide-tabbar-description = Cuddio'r bar tab pan mai dim ond un tab sydd ar agor
+system-integration-legend = Integreiddio System
+always-check-default =
+    .label = Gwirio bob tro os { -brand-short-name } yw'r rhaglen e-bost rhagosodedig wrth gychwyn
+    .accesskey = G
+check-default-button =
+    .label = Gwiriwch Nawr…
+    .accesskey = N
+# Note: This is the search engine name for all the different platforms.
+# Platforms that don't support it should be left blank.
+search-engine-name =
+    { PLATFORM() ->
+        [macos] Sbotolau
+        [windows] Chwilio Ffenestri
+       *[other] { "" }
+    }
+search-integration-label =
+    .label = Caniatáu i { search-engine-name } chwilio drwy'r negeseuon
+    .accesskey = C
+config-editor-button =
+    .label = Golygydd Ffurfweddu…
+    .accesskey = F
+return-receipts-description = Pennu sut mae { -brand-short-name } yn trin derbynebau
+return-receipts-button =
+    .label = Derbynebau Dychwelyd…
+    .accesskey = D
+update-app-legend = Diweddariadau { -brand-short-name }
+# Variables:
+#   $version (String): version of Thunderbird, e.g. 68.0.1
+update-app-version = Fersiwn { $version }
+allow-description = Gadael i { -brand-short-name } wneud
+automatic-updates-label =
+    .label = Gosod diweddariadau'n awtomatig (argymell: gwella diogelwch)
+    .accesskey = a
+check-updates-label =
+    .label = Gwirio am ddiweddariadau, ond gadael i mi ddewis i'w gosod a'i peidio
+    .accesskey = d
+update-history-button =
+    .label = Dangos Hanes Diweddaru
+    .accesskey = D
+use-service =
+    .label = Defnyddio gwasanaethau cefndirol i osod diweddariadau
+    .accesskey = e
+cross-user-udpate-warning = Bydd y gosodiad hwn yn berthnasol i holl gyfrifon Windows a phroffiliau { -brand-short-name } sy'n ddefnyddio'r gosodiad hwn { -brand-short-name }.
+networking-legend = Cysylltiad
+proxy-config-description = Ffurfweddu sut mae { -brand-short-name } yn cysylltu â'r Rhyngrwyd
+network-settings-button =
+    .label = Gosodiadau…
+    .accesskey = G
+offline-legend = All-lein
+offline-settings = Ffurfweddi gosodiadau all-lein
+offline-settings-button =
+    .label = All-lein…
+    .accesskey = l
+diskspace-legend = Lle ar Ddisg
+offline-compact-folder =
+    .label = Cywasgu pob ffolder pan fydd yn cadw dros gyfanswm o
+    .accesskey = y
+offline-compact-folder-automatically =
+    .label = Gofyn bob tro cyn cywasgu
+    .accesskey = G
+compact-folder-size =
+    .value = MB
+
+## Note: The entities use-cache-before and use-cache-after appear on a single
+## line in preferences as follows:
+## use-cache-before [ textbox for cache size in MB ] use-cache-after
+
+use-cache-before =
+    .value = Defnyddio hyd at
+    .accesskey = D
+use-cache-after = MB o le disg ar gyfer y storfa
+
+##
+
+smart-cache-label =
+    .label = Anwybyddu rheolaeth storfa awtomatig
+    .accesskey = A
+clear-cache-button =
+    .label = Clirio Nawr
+    .accesskey = N
+clear-cache-shutdown-label =
+    .label = Clirio'r storfa wrth gau
+    .accesskey = g
+fonts-legend = Ffontiau a Lliwiau
+default-font-label =
+    .value = Ffont rhagosodedig:
+    .accesskey = r
+default-size-label =
+    .value = Maint:
+    .accesskey = M
+font-options-button =
+    .label = Uwch…
+    .accesskey = U
+color-options-button =
+    .label = Lliwiau…
+    .accesskey = L
+display-width-legend = Negeseuon Testun Plaen
+# Note : convert-emoticons-label 'Emoticons' are also known as 'Smileys', e.g. :-)
+convert-emoticons-label =
+    .label = Dangos gwenogluniau fel graffigau
+    .accesskey = g
+display-text-label = Wrth ddangos negeseuon testun plaen dyfynedig:
+style-label =
+    .value = Arddull:
+    .accesskey = A
+regular-style-item =
+    .label = Arferol
+bold-style-item =
+    .label = Trwm
+italic-style-item =
+    .label = Italig
+bold-italic-style-item =
+    .label = Italig Trwm
+size-label =
+    .value = Maint:
+    .accesskey = M
+regular-size-item =
+    .label = Arferol
+bigger-size-item =
+    .label = Mwy
+smaller-size-item =
+    .label = Llai
+quoted-text-color =
+    .label = Lliw:
+    .accesskey = L
+search-handler-table =
+    .placeholder = Hidlo mathau a gweithredoedd cynnwys
+type-column-header = Math o Gynnwys
+action-column-header = Gweithred
+save-to-label =
+    .label = Cadw ffeiliau yn
+    .accesskey = C
+choose-folder-label =
+    .label =
+        { PLATFORM() ->
+            [macos] Dewis…
+           *[other] Pori…
+        }
+    .accesskey =
+        { PLATFORM() ->
+            [macos] D
+           *[other] P
+        }
+always-ask-label =
+    .label = Gofyn i mi lle i gadw pob ffeil
+    .accesskey = G
+display-tags-text = Mae modd defnyddio tagiau i gategoreiddio a blaenoriaethu eich negeseuon.
+new-tag-button =
+    .label = Newydd…
+    .accesskey = N
+edit-tag-button =
+    .label = Golygu…
+    .accesskey = G
+delete-tag-button =
+    .label = Dileu
+    .accesskey = D
+auto-mark-as-read =
+    .label = Marcio'n awtomatig negeseuon wedi'u darllen
+    .accesskey = a
+mark-read-no-delay =
+    .label = Dangos yn syth
+    .accesskey = s
+view-attachments-inline =
+    .label = Gweld atodiadau mewn llinell
+    .accesskey = G
+
+## Note: This will concatenate to "After displaying for [___] seconds",
+## using (mark-read-delay) and a number (seconds-label).
+
+mark-read-delay =
+    .label = Ar ôl dangos am
+    .accesskey = d
+seconds-label = eiliad
+
+##
+
+open-msg-label =
+    .value = Agor neges mewn:
+open-msg-tab =
+    .label = Tab newydd
+    .accesskey = T
+open-msg-window =
+    .label = Ffenestr neges newydd
+    .accesskey = n
+open-msg-ex-window =
+    .label = Ffenestr neges gyfredol
+    .accesskey = g
+close-move-delete =
+    .label = Cau ffenestr/tab neges wrth symud neu ddileu
+    .accesskey = C
+display-name-label =
+    .value = Enw dangos:
+condensed-addresses-label =
+    .label = Dangos dim ond enw dangos unigolion yn fy llyfr cyfeiriadau
+    .accesskey = D
+
+## Compose Tab
+
+forward-label =
+    .value = Anfon negeseuon ymlaen:
+    .accesskey = y
+inline-label =
+    .label = Mewnlin
+as-attachment-label =
+    .label = Fel Atodiad
+extension-label =
+    .label = ychwanegu estyniad i enw ffeil
+    .accesskey = e
+
+## Note: This will concatenate to "Auto Save every [___] minutes",
+## using (auto-save-label) and a number (auto-save-end).
+
+auto-save-label =
+    .label = Awto Gadw pob
+    .accesskey = G
+auto-save-end = munud
+
+##
+
+warn-on-send-accel-key =
+    .label = Cadarnhau wrth ddefnyddio llwybr byr bysellfwrdd i anfon neges
+    .accesskey = b
+add-link-previews =
+    .label = Ychwanegu rhagolygon dolenni wrth ludo URLau
+    .accesskey = Y
+spellcheck-label =
+    .label = Gwirio sillafu cyn anfon
+    .accesskey = s
+spellcheck-inline-label =
+    .label = Galluogi gwirio sillafu wrth deipio
+    .accesskey = E
+language-popup-label =
+    .value = Iaith:
+    .accesskey = I
+download-dictionaries-link = Llwytho i Lawr Rhagor o Eiriaduron
+font-label =
+    .value = Ffont:
+    .accesskey = F
+font-size-label =
+    .value = Maint:
+    .accesskey = M
+default-colors-label =
+    .label = Defnyddio lliwiau rhagosodedig y darllenydd
+    .accesskey = d
+font-color-label =
+    .value = Lliw Testun:
+    .accesskey = L
+bg-color-label =
+    .value = Lliw Cefndir:
+    .accesskey = C
+restore-html-label =
+    .label = Adfer y Rhagosodiadau
+    .accesskey = R
+default-format-label =
+    .label = Defnyddio'r Fformat Paragraff yn lle Testun Corff drwy ragosodiad
+    .accesskey = P
+compose-send-format-title = Fformat Anfon
+compose-send-automatic-option =
+    .label = Awtomatig
+compose-send-automatic-description = Os nad oes steilio'n cael ei ddefnyddio yn y neges, anfonwch Destun Plaen. Fel arall, anfonwch HTML gyda Thestun Plaen wrth gefn.
+compose-send-both-option =
+    .label = HTML a Thestun Plaen
+compose-send-both-description = Bydd rhaglen e-bost y derbynnydd yn pennu pa fersiwn i'w dangos.
+compose-send-html-option =
+    .label = Dim ond HTML
+compose-send-html-description = Efallai na fydd rhai derbynwyr yn gallu darllen y neges heb fod Testun Plaen wrth gefn.
+compose-send-plain-option =
+    .label = Dim ond Testun Plaen
+compose-send-plain-description = Bydd rhywfaint o steilio'n cael ei drosi i ddewis plaen arall, tra bydd nodweddion cyfansoddi eraill yn cael eu hanalluogi.
+autocomplete-description = Wrth gyfeirio negeseuon, chwilio am gofnodion cyfatebol yn:
+ab-label =
+    .label = Llyfrau Cyfeiriadau Lleol
+    .accesskey = L
+directories-label =
+    .label = Gweinydd Cyfeiriadur:
+    .accesskey = G
+directories-none-label =
+    .none = Dim
+edit-directories-label =
+    .label = Golygu Cyfeiriaduron…
+    .accesskey = C
+email-picker-label =
+    .label = Ychwanegu cyfeiriadau e-bost anfon yn awtomatig i'r:
+    .accesskey = Y
+default-directory-label =
+    .value = Cyfeiriadur cychwyn rhagosodedig yn ffenestr y llyfr cyfeiriadau:
+    .accesskey = c
+default-last-label =
+    .none = Cyfeiriadur defnyddiwyd ddiwethaf
+attachment-label =
+    .label = Gwirio am atodiadau coll
+    .accesskey = w
+attachment-options-label =
+    .label = Allweddeiriau…
+    .accesskey = w
+enable-cloud-share =
+    .label = Cynnig rhannu ffeiliau sy'n fwy na
+cloud-share-size =
+    .value = MB
+add-cloud-account =
+    .label = Ychwanegu…
+    .accesskey = Y
+    .defaultlabel = Ychwanegu…
+remove-cloud-account =
+    .label = Tynnu
+    .accesskey = T
+find-cloud-providers =
+    .value = Canfod rhagor o ddarparwyr…
+cloud-account-description = Ychwanegu gwasanaeth storio Filelink newydd
+
+## Privacy Tab
+
+mail-content = Cynnwys E-bost
+remote-content-label =
+    .label = Caniatáu cynnwys pell o fewn negeseuon
+    .accesskey = C
+exceptions-button =
+    .label = Eithriadau…
+    .accesskey = E
+remote-content-info =
+    .value = Dysgu rhagor am faterion preifatrwydd cynnwys pell
+web-content = Cynnwys Gwe
+history-label =
+    .label = Cofio gwefannau a dolenni rwyf wedi ymweld â nhw
+    .accesskey = o
+cookies-label =
+    .label = Derbyn cwcis gan wefannau
+    .accesskey = D
+third-party-label =
+    .value = Derbyn cwcis trydydd parti:
+    .accesskey = D
+third-party-always =
+    .label = Bob tro
+third-party-never =
+    .label = Byth
+third-party-visited =
+    .label = O'r ymwelwyd
+keep-label =
+    .value = Cadw tan:
+    .accesskey = C
+keep-expire =
+    .label = daw i ben
+keep-close =
+    .label = Cau { -brand-short-name }
+keep-ask =
+    .label = gofyn i mi bob tro
+cookies-button =
+    .label = Dangos Cwcis…
+    .accesskey = D
+do-not-track-label =
+    .label = Anfon neges “Dim Tracio” at wefannau nad ydych am gael eich tracio
+    .accesskey = D
+learn-button =
+    .label = Dysgu rhagor
+dnt-learn-more-button =
+    .value = Dysgu rhagor
+passwords-description = Mae { -brand-short-name } yn gallu cofio cyfrineiriau eich holl cyfrifon.
+passwords-button =
+    .label = Cyfrineiriau sydd wedi'u cadw…
+    .accesskey = C
+primary-password-description = Mae Prif Gyfrinair yn diogelu eich holl gyfrineiriau, ond rhaid i chi ei osod unwaith y sesiwn.
+primary-password-label =
+    .label = Defnyddio Prif Gyfrinair
+    .accesskey = D
+primary-password-button =
+    .label = Newid y Prif Gyfrinair…
+    .accesskey = N
+forms-primary-pw-fips-title = Rydych ym modd FIPS. Mae FIPS angen Prif Gyfrinair nad yw'n wag.
+forms-master-pw-fips-desc = Methodd Newid eich Cyfrinair
+junk-description = Yma gallwch osod eich gosodiadau sbam rhagosodedig. Mae modd ffurfweddu gosodiadau penodol ar gyfer sbam yn Gosodiadau Cyfrif.
+junk-label =
+    .label = Pan fyddai'n marcio negeseuon fel sbam:
+    .accesskey = P
+junk-move-label =
+    .label = Eu symud i ffolder "Sbam" y cyfrif
+    .accesskey = b
+junk-delete-label =
+    .label = Eu dileu
+    .accesskey = d
+junk-read-label =
+    .label = Marcio negeseuon Sbam fel rhai wedi'u darllen
+    .accesskey = a
+junk-log-label =
+    .label = Galluogi cofnodi hidlo sbam addasol
+    .accesskey = G
+junk-log-button =
+    .label = Dangos y cofnod
+    .accesskey = c
+reset-junk-button =
+    .label = Ailosod Data Hyfforddi
+    .accesskey = A
+phishing-description = Mae { -brand-short-name } yn gallu dadansoddi negeseuon am dwyll e-bost drwy edrych am dechnegau cyffredin i'ch twyllo.
+phishing-label =
+    .label = Dweud wrthyf os yw'r neges ryw'n ei darllen o bosib yn e-bost twyllodrus
+    .accesskey = D
+antivirus-description = Mae { -brand-short-name } yn gallu ei gwneud yn hawdd i feddalwedd gwrth firws ddadansoddi negeseuon e-byst sy'n cael eu derbyn am firysau cyn eu storio'n lleol.
+antivirus-label =
+    .label = Caniatáu i'r rhaglen neilltuo negeseuon sy'n cael eu derbyn
+    .accesskey = a
+certificate-description = Pan fydd gweinydd yn gofyn am fy nhystysgrif bersonol:
+certificate-auto =
+    .label = Dewis un yn awtomatig
+    .accesskey = D
+certificate-ask =
+    .label = Gofyn i mi bob tro
+    .accesskey = G
+ocsp-label =
+    .label = Ymholi gweinyddion ymatebydd OCSP i gadarnhau dilysrwydd cyfredol y tystysgrifau
+    .accesskey = Y
+certificate-button =
+    .label = Rheoli Tystysgrifau…
+    .accesskey = R
+security-devices-button =
+    .label = Dyfeisiau Diogelwch…
+    .accesskey = D
+email-e2ee-header = Amgryptio E-bost Pen-i-Ben
+account-settings = Gosodiadau Cyfrif
+email-e2ee-enable-info = Gosodwch gyfrifon e-bost a manylion adnabod Amgryptio o Ben-i-Ben yn Gosodiadau Cyfrif.
+email-e2ee-automatism = Defnydd Awtomatig o Amgryptio
+email-e2ee-automatism-pre = Gall { -brand-short-name } gynorthwyo drwy alluogi neu analluogi amgryptio yn awtomatig wrth ysgrifennu e-byst. Mae awto alluogi/analluogi yn seiliedig ar argaeledd allweddi neu dystysgrifau gohebwyr dilys a derbyniol.
+email-e2ee-auto-on =
+    .label = Galluogi amgryptio yn awtomatig pan fo modd
+email-e2ee-auto-off =
+    .label = Analluogi amgryptio yn awtomatig pan fydd derbynwyr yn newid ac nid yw amgryptio bellach yn bosibl
+email-e2ee-auto-off-notify =
+    .label = Dangos hysbysiad pryd bynnag mae amgryptio wedi'i analluogi'n awtomatig
+email-e2ee-automatism-post = Gall penderfyniadau awtomatig gael eu diystyru trwy alluogi neu analluogi amgryptio wrth ysgrifennu neges. Nodyn: mae amgryptio bob tro'n cael ei alluogi'n awtomatig wrth ateb neges wedi'i hamgryptio.
+
+## Chat Tab
+
+startup-label =
+    .value = Pan fydd { -brand-short-name } yn cychwyn:
+    .accesskey = P
+offline-label =
+    .label = Cadw fy Nghyfrifon Sgwrsio all-lein
+auto-connect-label =
+    .label = Cysylltu â fy nghyfrifon sgwrsio yn awtomatig
+
+## Note: idle-label is displayed first, then there's a field where the user
+## can enter a number, and itemTime is displayed at the end of the line.
+## The translations of the idle-label and idle-time-label parts don't have
+## to mean the exact same thing as in English; please try instead to
+## translate the whole sentence.
+
+idle-label =
+    .label = Hysbysu fy nghysylltiadau fy mod yn Segur ar ôl
+    .accesskey = S
+idle-time-label = munud o seibiant
+
+##
+
+away-message-label =
+    .label = a dynodi fy statws i I Ffwrdd gyda'r neges statws yma:
+    .accesskey = F
+send-typing-label =
+    .label = Anfon hysbysiadau teipio mewn trafodaethau
+    .accesskey = h
+notification-label = Pan fydd negeseuon wedi eu cyfeirio atoch chi yn cyrraedd:
+show-notification-label =
+    .label = Dangos rhybudd:
+    .accesskey = r
+notification-all =
+    .label = gydag enw'r anfonwr a rhagolwg o'r neges
+notification-name =
+    .label = gydag enw'r anfonwr yn unig
+notification-empty =
+    .label = heb unrhyw wybodaeth
+notification-type-label =
+    .label =
+        { PLATFORM() ->
+            [macos] Animeiddio eitem docio
+           *[other] Fflachio'r eitem bar tasgau
+        }
+    .accesskey =
+        { PLATFORM() ->
+            [macos] o
+           *[other] F
+        }
+chat-play-sound-label =
+    .label = Canu nodyn
+    .accesskey = C
+chat-play-button =
+    .label = Chwarae
+    .accesskey = h
+chat-system-sound-label =
+    .label = Sain rhagosodedig y system ar gyfer e-bost newydd
+    .accesskey = S
+chat-custom-sound-label =
+    .label = Defnyddio'r ffeil sain ganlynol
+    .accesskey = D
+chat-browse-sound-button =
+    .label = Pori…
+    .accesskey = P
+theme-label =
+    .value = Thema:
+    .accesskey = T
+style-mail =
+    .label = { -brand-short-name }
+style-bubbles =
+    .label = Swigod
+style-dark =
+    .label = Tywyll
+style-paper =
+    .label = Dalennau Papur
+style-simple =
+    .label = Syml
+preview-label = Rhagolwg:
+no-preview-label = Dim rhagolwg ar gael
+no-preview-description = Nid yw'r thema yma'n ddilys nac ar gael ar hyn o bryd (ychwanegyn wedi ei analluogi, modd diogel, …).
+chat-variant-label =
+    .value = Amrywiad:
+    .accesskey = A
+# This is used to determine the width of the search field in about:preferences,
+# in order to make the entire placeholder string visible
+#
+# Please keep the placeholder string short to avoid truncation.
+#
+# Notice: The value of the `.style` attribute is a CSS string, and the `width`
+# is the name of the CSS property. It is intended only to adjust the element's width.
+# Do not translate.
+search-preferences-input2 =
+    .style = width: 15.4em
+    .placeholder = Canfod yn y Gosodiadau
+
+## Settings UI Search Results
+
+search-results-header = Canlyniadau Chwilio
+# `<span data-l10n-name="query"></span>` will be replaced by the search term.
+search-results-empty-message2 =
+    { PLATFORM() ->
+        [windows] Ymddiheuriadau! Nid oes canlyniadau yn y Dewisiadau ar gyfer “<span data-l10n-name="query"></span>”.
+       *[other] Ymddiheuriadau! Nid oes canlyniadau yn y Dewisiadau ar gyfer “<span data-l10n-name="query"></span>”.
+    }
+search-results-help-link = Angen cymorth? Ewch i <a data-l10n-name="url">Cefnogaeth { -brand-short-name }</a>
+
+## Sync Tab
+
+sync-signedout-caption = Cymrwch eich Gwe gyda Chi
+sync-signedout-description = Cydweddwch eich cyfrifon, llyfrau cyfeiriadau, calendrau, ychwanegion a gosodiadau ar draws eich holl ddyfeisiau.
+# Note: "Sync" represents the Firefox Sync product so it shouldn't be translated.
+sync-signedout-account-signin-btn = Mewngofnodi i Sync…
+sync-pane-header = Cydweddu
+# Variables:
+# $userEmail (String) - The email logged into Sync.
+sync-pane-email-not-verified = Nid yw " { $userEmail } " wedi'i wirio.
+# Variables:
+# $userEmail (String) - The email logged into Sync.
+sync-signedin-login-failure = Mewngofnodwch i ailgysylltu “{ $userEmail }”
+sync-pane-resend-verification = Ail Anfon Dilysiad
+sync-pane-sign-in = Mewngofnodi
+sync-pane-remove-account = Tynnu cyfrif
+sync-pane-edit-photo =
+    .title = Newid llun proffil
+sync-pane-manage-account = Rheoli cyfrif
+sync-pane-sign-out = Allgofnodi…
+sync-pane-device-name-title = Enw Dyfais
+sync-pane-change-device-name = Newid enw dyfais
+sync-pane-cancel = Diddymu
+sync-pane-save = Cadw
+sync-pane-show-synced-header-on = Cydweddu YMLAEN
+sync-pane-show-synced-header-off = Cydweddu I FFWRDD
+sync-pane-sync-now = Cydweddu Nawr
+sync-panel-sync-now-syncing = Cydweddu…
+show-synced-list-heading = Rydych wrthi'n cydweddu'r eitemau hyn:
+show-synced-learn-more = Dysgu rhagor…
+show-synced-item-account = Cyfrifon E-bost
+show-synced-item-address = Llyfrau Cyfeiriadau
+show-synced-item-calendar = Calendrau
+show-synced-item-identity = Hunaniaethau
+show-synced-item-passwords = Cyfrineiriau
+show-synced-change = Newid…
+synced-acount-item-server-config = Ffufweddiad gweinydd
+synced-acount-item-filters = Hidlau
+synced-acount-item-keys = OpenPGP - S/MIME
+sync-disconnected-text = Cydweddwch eich cyfrifon e-bost, llyfrau cyfeiriadau, calendrau a hunaniaethau ar draws eich holl ddyfeisiau.
+sync-disconnected-turn-on-sync = Cychwyn Cydweddu…
diff --git a/thunderbird-l10n/cy/localization/cy/messenger/preferences/receipts.ftl b/thunderbird-l10n/cy/localization/cy/messenger/preferences/receipts.ftl
new file mode 100644
index 0000000000..b9c2784ad1
--- /dev/null
+++ b/thunderbird-l10n/cy/localization/cy/messenger/preferences/receipts.ftl
@@ -0,0 +1,39 @@
+# This Source Code Form is subject to the terms of the Mozilla Public
+# License, v. 2.0. If a copy of the MPL was not distributed with this
+# file, You can obtain one at http://mozilla.org/MPL/2.0/.
+
+receipts-dialog-window =
+    .title = Derbynebau Dychwelyd
+receipts-dialog-title = Derbynebau Dychwelyd
+return-receipt-checkbox-control =
+    .label = Wrth anfon negeseuon, gofyn bob tro am dderbynneb dychwelyd
+    .accesskey = a
+receipt-arrive-label = Pan fydd derbynneb yn cyrraedd:
+receipt-leave-radio-control =
+    .label = Gadael yn fy Mlwch Derbyn
+    .accesskey = G
+receipt-move-radio-control =
+    .label = Symud i fy ffolder "Anfonwyd"
+    .accesskey = S
+receipt-request-label = Pan fyddaf yn derbyn cais am dderbynneb dychwelyd:
+receipt-return-never-radio-control =
+    .label = Peidio ag anfon derbynneb dychwelyd
+    .accesskey = P
+receipt-return-some-radio-control =
+    .label = Caniatáu derbynebau dychwelyd ar gyfer rhai negeseuon
+    .accesskey = C
+receipt-not-to-cc-label =
+    .value = Os nad wyf yn At neu Cc y neges:
+    .accesskey = O
+receipt-send-never-label =
+    .label = Byth anfon
+receipt-send-always-label =
+    .label = Anfon pob tro
+receipt-send-ask-label =
+    .label = Gofyn i mi
+sender-outside-domain-label =
+    .value = Os yw'r anfonwr o'r tu allan i'm parth:
+    .accesskey = s
+other-cases-text-label =
+    .value = Ym mhob achos arall:
+    .accesskey = Y
diff --git a/thunderbird-l10n/cy/localization/cy/messenger/preferences/sync-dialog.ftl b/thunderbird-l10n/cy/localization/cy/messenger/preferences/sync-dialog.ftl
new file mode 100644
index 0000000000..06deb39dea
--- /dev/null
+++ b/thunderbird-l10n/cy/localization/cy/messenger/preferences/sync-dialog.ftl
@@ -0,0 +1,11 @@
+# This Source Code Form is subject to the terms of the Mozilla Public
+# License, v. 2.0. If a copy of the MPL was not distributed with this
+# file, You can obtain one at http://mozilla.org/MPL/2.0/.
+
+config-sync-dailog-title =
+    .title = Dewis beth i gydweddu
+sync-dialog =
+    .buttonlabelaccept = Cadw Newidiadau
+    .buttonaccesskeyaccept = N
+    .buttonlabelextra2 = Datgysylltu…
+    .buttonaccesskeyextra2 = D
diff --git a/thunderbird-l10n/cy/localization/cy/messenger/preferences/system-integration.ftl b/thunderbird-l10n/cy/localization/cy/messenger/preferences/system-integration.ftl
new file mode 100644
index 0000000000..95a68ef18a
--- /dev/null
+++ b/thunderbird-l10n/cy/localization/cy/messenger/preferences/system-integration.ftl
@@ -0,0 +1,39 @@
+# This Source Code Form is subject to the terms of the Mozilla Public
+# License, v. 2.0. If a copy of the MPL was not distributed with this
+# file, You can obtain one at http://mozilla.org/MPL/2.0/.
+
+system-integration-title =
+    .title = Integreiddio System
+system-integration-dialog-title = Integreiddio System
+system-integration-dialog =
+    .buttonlabelaccept = Gosod fel y Rhagosodiad
+    .buttonlabelcancel = Hepgor Integreiddio
+    .buttonlabelcancel2 = Diddymu
+default-client-intro = Defnyddio { -brand-short-name } fel y rhaglen rhagosodedig ar gyfer:
+unset-default-tooltip = Nid yw'n bosib dadosod { -brand-short-name } fel y cleient rhagosodedig o fewn { -brand-short-name }. I wneud rhaglen arall y rhagosodedig rhaid defnyddio ei ddeialog 'Gosod fel y rhagosodedig' ei hun.
+checkbox-email-label =
+    .label = E-Bost
+    .tooltiptext = { unset-default-tooltip }
+checkbox-newsgroups-label =
+    .label = Grwpiau Newyddion
+    .tooltiptext = { unset-default-tooltip }
+checkbox-feeds-label =
+    .label = Llif
+    .tooltiptext = { unset-default-tooltip }
+checkbox-calendar-label =
+    .label = Calendr
+    .tooltiptext = { unset-default-tooltip }
+# Note: This is the search engine name for all the different platforms.
+# Platforms that don't support it should be left blank.
+system-search-engine-name =
+    { PLATFORM() ->
+        [macos] Sbotolau
+        [windows] Chwilio Ffenestri
+       *[other] { "" }
+    }
+system-search-integration-label =
+    .label = Caniatáu i { system-search-engine-name } chwilio drwy'r negeseuon
+    .accesskey = C
+check-on-startup-label =
+    .label = Gwirio hwn bob tro wrth gychwyn { -brand-short-name }
+    .accesskey = G
diff --git a/thunderbird-l10n/cy/localization/cy/messenger/shortcuts.ftl b/thunderbird-l10n/cy/localization/cy/messenger/shortcuts.ftl
new file mode 100644
index 0000000000..6d77e41549
--- /dev/null
+++ b/thunderbird-l10n/cy/localization/cy/messenger/shortcuts.ftl
@@ -0,0 +1,113 @@
+# This Source Code Form is subject to the terms of the Mozilla Public
+# License, v. 2.0. If a copy of the MPL was not distributed with this
+# file, You can obtain one at http://mozilla.org/MPL/2.0/.
+
+
+## Shortcuts
+
+# Variables:
+#  $key (String) - The shortcut key.
+shortcut-key = { $key }
+
+meta-shortcut-key =
+    { PLATFORM() ->
+        [macos] ⌘ { $key }
+       *[other] Meta+{ $key }
+    }
+
+ctrl-shortcut-key =
+    { PLATFORM() ->
+        [macos] ⌃ { $key }
+       *[other] Ctrl+{ $key }
+    }
+
+shift-shortcut-key =
+    { PLATFORM() ->
+        [macos] ⇧ { $key }
+       *[other] Shift+{ $key }
+    }
+
+alt-shortcut-key =
+    { PLATFORM() ->
+        [macos] Shift+{ $key }
+       *[other] Alt+{ $key }
+    }
+
+meta-ctrl-shortcut-key =
+    { PLATFORM() ->
+        [macos] ⌃ ⌘ { $key }
+       *[other] Meta+Ctrl+{ $key }
+    }
+
+meta-alt-shortcut-key =
+    { PLATFORM() ->
+        [macos] ⌥ ⌘ { $key }
+       *[other] Meta+Alt+{ $key }
+    }
+
+ctrl-alt-shortcut-key =
+    { PLATFORM() ->
+        [macos] ⌃ ⌥ { $key }
+       *[other] Ctrl+Alt+{ $key }
+    }
+
+meta-ctrl-alt-shortcut-key =
+    { PLATFORM() ->
+        [macos] ⌃ ⌥ ⌘ { $key }
+       *[other] Meta+Ctrl+Alt+{ $key }
+    }
+
+meta-shift-shortcut-key =
+    { PLATFORM() ->
+        [macos] ⇧ ⌘ { $key }
+       *[other] Meta+Shift+{ $key }
+    }
+
+ctrl-shift-shortcut-key =
+    { PLATFORM() ->
+        [macos] ⌃ ⇧ { $key }
+       *[other] Ctrl+Shift+{ $key }
+    }
+
+meta-ctrl-shift-shortcut-key =
+    { PLATFORM() ->
+        [macos] ⌃ ⇧ ⌘ { $key }
+       *[other] Meta+Ctrl+Shift+{ $key }
+    }
+
+alt-shift-shortcut-key =
+    { PLATFORM() ->
+        [macos] ⌥ ⇧ { $key }
+       *[other] Alt+Shift+{ $key }
+    }
+
+meta-shift-alt-shortcut-key2 =
+    { PLATFORM() ->
+        [macos] ⌥ ⇧ ⌘ { $key }
+       *[other] Meta+Alt+Shift+{ $key }
+    }
+
+ctrl-shift-alt-shortcut-key2 =
+    { PLATFORM() ->
+        [macos] ⌃ ⌥ ⇧ { $key }
+       *[other] Ctrl+Alt+Shift+{ $key }
+    }
+
+meta-ctrl-shift-alt-shortcut-key2 =
+    { PLATFORM() ->
+        [macos] ⌃ ⌥ ⇧ ⌘ { $key }
+       *[other] Meta+Ctrl+Alt+Shift+{ $key }
+    }
+
+# Variables:
+#  $title (String): The title coming from the original element.
+#  $shortcut (String): The shortcut generated from the keystroke combination.
+button-shortcut-string =
+    .title = { $title } ({ $shortcut })
+
+# Variables:
+#  $label (String): The text label coming from the original element.
+#  $shortcut (String): The shortcut generated from the keystroke combination.
+menuitem-shortcut-string =
+    .label = { $label }
+    .acceltext = { $shortcut }
diff --git a/thunderbird-l10n/cy/localization/cy/messenger/syncAccounts.ftl b/thunderbird-l10n/cy/localization/cy/messenger/syncAccounts.ftl
new file mode 100644
index 0000000000..d05b80e7a3
--- /dev/null
+++ b/thunderbird-l10n/cy/localization/cy/messenger/syncAccounts.ftl
@@ -0,0 +1,28 @@
+# This Source Code Form is subject to the terms of the Mozilla Public
+# License, v. 2.0. If a copy of the MPL was not distributed with this
+# file, you can obtain one at http://mozilla.org/MPL/2.0/.
+
+
+# The strings in this file relate to the configuration of Mozilla accounts for sync.
+
+
+## These strings are shown in a desktop notification after the user requests we resend a verification email.
+
+sync-verification-sent-title = Dilysiad wedi'i Anfon
+# Variables:
+# $userEmail (String) - Email address of the account used for sync.
+sync-verification-sent-body = Mae dolen dilysu wedi'i anfon at { $userEmail }.
+sync-verification-not-sent-title = Methu Anfon Dilysiad
+sync-verification-not-sent-body = Nid ydym yn gallu anfon e-bost dilysu ar hyn o bryd, ceisiwch eto'n hwyrach.
+
+## These strings are shown in a confirmation dialog when the user chooses to sign out.
+
+sync-signout-dialog-title = Allgofnodi o gyfrif?
+sync-signout-dialog-body = Bydd data wedi'i gydweddu'n aros yn eich cyfrif.
+sync-signout-dialog-button = Allgofnodi
+
+## These strings are shown in a confirmation dialog when the user chooses to stop syncing.
+
+sync-disconnect-dialog-title = Datgysylltu?
+sync-disconnect-dialog-body = Bydd { -brand-product-name } yn datgysylltu o'ch cyfrif ond ni fydd yn dileu dim o'ch data pori ar y ddyfais hon.
+sync-disconnect-dialog-button = Datgysylltu
diff --git a/thunderbird-l10n/cy/localization/cy/messenger/treeView.ftl b/thunderbird-l10n/cy/localization/cy/messenger/treeView.ftl
new file mode 100644
index 0000000000..1199c94cb1
--- /dev/null
+++ b/thunderbird-l10n/cy/localization/cy/messenger/treeView.ftl
@@ -0,0 +1,65 @@
+# This Source Code Form is subject to the terms of the Mozilla Public
+# License, v. 2.0. If a copy of the MPL was not distributed with this
+# file, You can obtain one at http://mozilla.org/MPL/2.0/.
+
+
+## Table
+
+tree-list-view-row-select =
+    .alt = Y blwch ticio i newid dewis y rhes gyfredol
+    .title = Dewis y rhes gyfredol
+tree-list-view-row-deselect =
+    .alt = Y blwch ticio i newid dewis y rhes gyfredol
+    .title = Dad-ddewis y rhes gyfredol
+tree-list-view-row-delete =
+    .title = Dileu'r rhes gyfredol
+tree-list-view-row-restore =
+    .title = Adfer y rhes gyfredol
+tree-list-view-column-picker =
+    .title = Dewis colofnau i'w dangos
+tree-list-view-column-picker-restore =
+    .label = Adfer trefn colofnau
+tree-list-view-row-thread-icon =
+    .alt = Dangosydd trywydd newydd
+    .title = Mae hwn yn neges ar drywydd
+tree-list-view-row-thread-button =
+    .title = Mae hwn yn neges ar drywydd
+tree-list-view-row-ignored-thread = Anwybyddu trywydd
+tree-list-view-row-ignored-thread-icon =
+    .alt = Dangosydd trywydd newydd
+    .title = Mae'r neges ar drywydd hwn wedi'i anwybyddu
+tree-list-view-row-ignored-thread-button =
+    .title = Mae'r neges ar drywydd hwn wedi'i anwybyddu
+tree-list-view-row-ignored-subthread = Is drywyddd wedi'i anwybyddu
+tree-list-view-row-ignored-subthread-icon =
+    .alt = Dangosydd trywydd newydd
+    .title = Mae'r is drywydd  wedi'i anwybyddu
+tree-list-view-row-ignored-subthread-button =
+    .title = Mae'r is drywydd  wedi'i anwybyddu
+tree-list-view-row-watched-thread = Trywydd yn cael ei wylio
+tree-list-view-row-watched-thread-icon =
+    .alt = Dangosydd trywydd newydd
+    .title = Mae'r trywydd hwn yn cael ei wylio
+tree-list-view-row-watched-thread-button =
+    .title = Mae'r trywydd hwn yn cael ei wylio
+tree-list-view-row-flagged =
+    .alt = Dangosydd neges serennog
+    .title = Neges serennog
+tree-list-view-row-flag =
+    .alt = Dangosydd neges serennog
+    .title = Nid yw'n neges serennog
+tree-list-view-row-attach =
+    .alt = Dangosydd atodiadau
+    .title = Mae'r neges yn cynnwys atodiad(au)
+tree-list-view-row-spam =
+    .alt = Dangosydd statws sbam
+    .title = Neges wedi'i marcio fel sbam
+tree-list-view-row-not-spam =
+    .alt = Dangosydd statws sbam
+    .title = Neges heb ei marcio fel sbam
+tree-list-view-row-read =
+    .alt = Dangosydd statws darllen
+    .title = Statws darllen neges
+tree-list-view-row-not-read =
+    .alt = Dangosydd statws heb ei ddarllen
+    .title = Statws neges heb ei darllen
diff --git a/thunderbird-l10n/cy/localization/cy/messenger/troubleshootMode.ftl b/thunderbird-l10n/cy/localization/cy/messenger/troubleshootMode.ftl
new file mode 100644
index 0000000000..61ce7693b7
--- /dev/null
+++ b/thunderbird-l10n/cy/localization/cy/messenger/troubleshootMode.ftl
@@ -0,0 +1,33 @@
+# This Source Code Form is subject to the terms of the Mozilla Public
+# License, v. 2.0. If a copy of the MPL was not distributed with this
+# file, You can obtain one at http://mozilla.org/MPL/2.0/.
+
+troubleshoot-mode-window =
+    .title = Modd Datrys Problemau { -brand-short-name }
+    .style = width: 37em;
+troubleshoot-mode-dialog-title = Modd Datrys Problemau { -brand-short-name }
+troubleshoot-mode-description = Defnyddiwch y modd arbennig hwn o { -brand-short-name } i ddatrys materion. Bydd eich estyniadau a'ch cyfaddasiadau yn cael eu hanalluogi dros dro.
+troubleshoot-mode-description2 = Gallwch wneud rhai neu'r cyfan o'r newidiadau hyn yn rhai parhaol:
+troubleshoot-mode-disable-addons =
+    .label = Analluogi pob ychwanegyn
+    .accesskey = A
+troubleshoot-mode-reset-toolbars =
+    .label = Ailosod barau offer a rheolyddion
+    .accesskey = b
+troubleshoot-mode-change-and-restart =
+    .label = Gwneud Newidiadau ac Ailgychwyn
+    .accesskey = G
+troubleshoot-mode-continue =
+    .label = Parhau yn y Modd Datrys Problemau
+    .accesskey = P
+troubleshoot-mode-quit =
+    .label =
+        { PLATFORM() ->
+            [windows] Gadael
+           *[other] Gorffen
+        }
+    .accesskey =
+        { PLATFORM() ->
+            [windows] a
+           *[other] o
+        }
diff --git a/thunderbird-l10n/cy/localization/cy/messenger/unifiedToolbar.ftl b/thunderbird-l10n/cy/localization/cy/messenger/unifiedToolbar.ftl
new file mode 100644
index 0000000000..80b40331ec
--- /dev/null
+++ b/thunderbird-l10n/cy/localization/cy/messenger/unifiedToolbar.ftl
@@ -0,0 +1,100 @@
+# This Source Code Form is subject to the terms of the Mozilla Public
+# License, v. 2.0. If a copy of the MPL was not distributed with this
+# file, You can obtain one at http://mozilla.org/MPL/2.0/.
+
+
+### Unified Toolbar strings
+
+
+## Search bar
+
+search-bar-button =
+    .alt = Chwilio
+search-bar-item =
+    .label = Chwilio:
+search-bar-placeholder = Chwilio…
+# Search bar placeholder with formatted key shortcut hint (platform dependent).
+# The key after the control modifier should match the key from quickSearchCmd.key
+# in messenger.dtd.
+search-bar-placeholder-with-key2 =
+    { PLATFORM() ->
+        [macos] { search-bar-placeholder } <kbd>⌘</kbd> <kbd>K</kbd>
+       *[other] { search-bar-placeholder } <kbd>Ctrl</kbd> + <kbd>K</kbd>
+    }
+
+## Unified toolbar context menu
+
+customize-menu-customize =
+    .label = Cyfaddasu…
+
+# Unified toolbar get messages button context menu
+
+toolbar-get-all-messages-menuitem =
+    .label = Estyn Pob Neges Newydd
+    .accesskey = E
+
+## Unified Toolbar customization
+
+customize-title = Cyfaddasu Bariau Offer
+customize-space-tab-mail = E-bost
+    .title = E-bost
+customize-space-tab-addressbook = Llyfr Cyfeiriadau
+    .title = Llyfr Cyfeiriadau
+customize-space-tab-calendar = Calendr
+    .title = Calendr
+customize-space-tab-tasks = Tasgau
+    .title = Tasgau
+customize-space-tab-chat = Sgwrsio
+    .title = Sgwrsio
+customize-space-tab-settings = Gosodiadau
+    .title = Gosodiadau
+customize-restore-default = Adfer y rhagosodiadau
+customize-change-appearance = Newid golwg…
+customize-button-style-label = Arddull botwm:
+customize-button-style-icons-beside-text-option = Eiconau gerllaw testun
+customize-button-style-icons-above-text-option = Eiconau uwchben testun
+customize-button-style-icons-only-option = Eiconau yn unig
+customize-button-style-text-only-option = Testun yn unig
+customize-cancel = Diddymu
+customize-save = Cadw
+customize-unsaved-changes = Newidiadau heb eu cadw mewn mannau eraill
+customize-search-bar =
+    .label = Botymau bar offer chwilio…
+customize-spaces-tabs =
+    .aria-label = Mannau
+customize-main-toolbar-target =
+    .aria-label = Prif bar offer
+customize-palette-generic-title = Ar gael ar gyfer pob Man
+customize-palette-mail-specific-title = Ar gael ar gyfer Man E-bost yn unig
+customize-palette-addressbook-specific-title = Ar gael ar gyfer Man Llyfr Cyfeiriadau'n unig
+customize-palette-calendar-specific-title = Ar gael ar gyfer Man Calendr yn unig
+customize-palette-tasks-specific-title = Ar gael ar gyfer Man Tasgau'n unig
+customize-palette-chat-specific-title = Ar gael ar gyfer Man Sgwrsio'n unig
+customize-palette-settings-specific-title = Ar gael ar gyfer Man Gosodiadau'n unig
+customize-palette-extension-specific-title = Ar gael ar gyfer y Bwlch hwn yn unig
+
+## Unified toolbar customization palette context menu
+
+# Variables:
+# $target (String) - Name of the target the item should be added to.
+customize-palette-add-to =
+    .label = Ychwanegu at { $target }
+customize-palette-add-everywhere =
+    .label = Ychwanegu at bob bar offer
+
+## Unified toolbar customization target context menu
+
+customize-target-forward =
+    .label = Symud ymlaen
+customize-target-backward =
+    .label = Symud nôl
+customize-target-remove =
+    .label = Tynnu
+customize-target-remove-everywhere =
+    .label = Tynnu o bob bar offer
+customize-target-add-everywhere =
+    .label = Ychwanegu at bob bar offer
+customize-target-start =
+    .label = Symud i'r cychwyn
+customize-target-end =
+    .label = Symud i'r diwedd
diff --git a/thunderbird-l10n/cy/localization/cy/messenger/unifiedToolbarItems.ftl b/thunderbird-l10n/cy/localization/cy/messenger/unifiedToolbarItems.ftl
new file mode 100644
index 0000000000..35f61f9bb4
--- /dev/null
+++ b/thunderbird-l10n/cy/localization/cy/messenger/unifiedToolbarItems.ftl
@@ -0,0 +1,165 @@
+# This Source Code Form is subject to the terms of the Mozilla Public
+# License, v. 2.0. If a copy of the MPL was not distributed with this
+# file, You can obtain one at http://mozilla.org/MPL/2.0/.
+
+
+### Unified Toolbar Item Label strings
+
+spacer-label = Bwlch Hyblyg
+search-bar-label = Chwilio
+toolbar-write-message-label = Ysgrifennu
+toolbar-write-message =
+    .title = Creu neges newydd
+toolbar-move-to-label = Symud I
+toolbar-move-to =
+    .title = Symud y neges a ddewiswyd
+toolbar-unifinder-label = Canfod Digwyddiadau
+toolbar-unifinder =
+    .title = Newid y paen canfod digwyddiadau
+toolbar-folder-location-label = Lleoliad Ffolder
+toolbar-folder-location =
+    .title = Newid i ffolder
+toolbar-edit-event-label = Golygu
+toolbar-edit-event =
+    .title = Golygu digwyddiadau neu dasgau penodol
+toolbar-get-messages-label = Estyn Negeseuon
+toolbar-get-messages =
+    .title = Estyn negeseuon newydd ar gyfer pob cyfrif
+toolbar-reply-label = Ateb
+toolbar-reply =
+    .title = Ateb y neges
+toolbar-reply-all-label = Ateb Pawb
+toolbar-reply-all =
+    .title = Ateb yr anfonwr a phob derbyniwr
+toolbar-reply-to-list-label = Ateb i'r Rhestr
+toolbar-reply-to-list =
+    .title = Ateb i'r rhestr e-bost
+toolbar-redirect-label = Ailgyfeirio
+toolbar-redirect =
+    .title = Ailgyfeirio'r neges hon
+toolbar-archive-label = Archifo
+toolbar-archive =
+    .title = Archifo'r negeseuon
+toolbar-conversation-label = Sgwrs
+toolbar-conversation =
+    .title = Dangos sgwrs neges sydd wedi ei dewis
+toolbar-previous-unread-label = Blaenorol Heb ei Darllen
+toolbar-previous-unread =
+    .title = Symud i'r neges heb ei darllen diwethaf
+toolbar-previous-label = Blaenorol
+toolbar-previous =
+    .title = Symud i'r neges flaenorol
+toolbar-next-unread-label = Nesaf Heb ei Darllen
+toolbar-next-unread =
+    .title = Symud i'r neges nesaf heb ei darllen
+toolbar-next-label = Nesaf
+toolbar-next =
+    .title = Symud i'r neges nesaf
+toolbar-junk-label = Sbam
+toolbar-junk =
+    .title = Marcio'r negeseuon hyn fel sbwriel
+toolbar-delete-label = Dileu
+toolbar-delete-title =
+    .title = Dileu'r negeseuon a ddewiswyd
+toolbar-undelete-label = Dad-ddileu
+toolbar-undelete =
+    .title = Dad-ddileu'r negeseuon a ddewiswyd
+toolbar-compact-label = Cywasgu
+toolbar-compact =
+    .title = Tynnu negeseuon wedi'u dileu o'r ffolder
+toolbar-add-as-event-label = Ychwanegu digwyddiad
+toolbar-add-as-event =
+    .title = Tynnu gwybodaeth calendr o'r neges a'i ychwanegu i'ch calendr fel digwyddiad
+toolbar-add-as-task-label = Ychwanegu fel tasg
+toolbar-add-as-task =
+    .title = Tynnu gwybodaeth calendr o'r neges a'i ychwanegu i'ch calendr fel tasg
+toolbar-tag-message-label = Tag
+toolbar-tag-message =
+    .title = Tagio negeseuon
+toolbar-forward-inline-label = Ymlaen
+toolbar-forward-inline =
+    .title = Anfon neges dewiswyd ymlaen fel testun mewnlin
+toolbar-forward-attachment-label = Anfon Ymlaen fel Atodiad
+toolbar-forward-attachment =
+    .title = Anfon neges dewiswyd ymlaen fel atodiad
+toolbar-mark-as-label = Marcio
+toolbar-mark-as =
+    .title = Marcio negeseuon
+toolbar-view-picker-label = Golwg
+toolbar-view-picker =
+    .title = Cyfaddasu golwg y ffolder gyfredol
+toolbar-address-book-label = Llyfr Cyfeiriadau
+toolbar-address-book =
+    .title = Mynd i'r llyfr cyfeiriadau
+toolbar-chat-label = Sgwrsio
+toolbar-chat =
+    .title = Dangos y tab Sgwrsio
+toolbar-add-ons-and-themes-label = Ychwanegion a Themâu
+toolbar-add-ons-and-themes =
+    .title = Rheoli eich ychwanegion
+toolbar-calendar-label = Calendr
+toolbar-calendar =
+    .title = Symud i'r tab calendr
+toolbar-tasks-label = Tasgau
+toolbar-tasks =
+    .title = Symud i'r tab tasgau
+toolbar-mail-label = E-bost
+toolbar-mail =
+    .title = Symud i'r tab e-bost
+toolbar-print-label = Argraffu
+toolbar-print =
+    .title = Argraffu'r neges
+toolbar-quick-filter-bar-label = Hidl Cyflym
+toolbar-quick-filter-bar =
+    .title = Hidlo negeseuon
+toolbar-synchronize-label = Cydweddu
+toolbar-synchronize =
+    .title = Ail-lwytho calendrau a chydweddu newidiadau
+toolbar-delete-event-label = Dileu
+toolbar-delete-event =
+    .title = Dileu digwyddiadau neu dasgau penodol
+toolbar-go-to-today-label = Mynd i Heddiw
+toolbar-go-to-today =
+    .title = Mynd i Heddiw
+toolbar-print-event-label = Argraffu
+toolbar-print-event =
+    .title = Argraffu digwyddiadau neu dasgau
+toolbar-new-event-label = Digwyddiad
+toolbar-new-event =
+    .title = Creu digwyddiad newydd
+toolbar-new-task-label = Tasg
+toolbar-new-task =
+    .title = Creu tasg newydd
+toolbar-go-back-label = Nôl
+toolbar-go-back =
+    .title = Mynd nôl un neges
+toolbar-go-forward-label = Ymlaen
+toolbar-go-forward =
+    .title = Mynd ymlaen un neges
+toolbar-stop-label = Atal
+toolbar-stop =
+    .title = Atal y trosglwyddiad cyfredol
+toolbar-throbber-label = Dangosydd Gweithgaredd
+toolbar-throbber =
+    .title = Dangosydd Gweithgaredd
+toolbar-create-contact-label = Cysylltiad Newydd
+toolbar-create-contact =
+    .title = Creu cyswllt newydd
+toolbar-create-address-book-label = Llyfr Cyfeiriadau Newydd
+toolbar-create-address-book =
+    .title = Creu llyfr cyfeiriadau newydd
+toolbar-create-list-label = Rhestr Newydd
+toolbar-create-list =
+    .title = Creu rhestr e-bostio newydd
+toolbar-import-contacts-label = Mewnforio
+toolbar-import-contacts =
+    .title = Mewnforio cysylltiadau o ffeil
+
+## New Address Book popup items
+
+toolbar-new-address-book-popup-add-js-address-book =
+    .label = Ychwanegu Llyfr Cyfeiriadau Lleol
+toolbar-new-address-book-popup-add-carddav-address-book =
+    .label = Ychwanegu Llyfr Cyfeiriadau CardDAV
+toolbar-new-address-book-popup-add-ldap-address-book =
+    .label = Ychwanegu Llyfr Cyfeiriadau LDAP
diff --git a/thunderbird-l10n/cy/localization/cy/messenger/viewSource.ftl b/thunderbird-l10n/cy/localization/cy/messenger/viewSource.ftl
new file mode 100644
index 0000000000..63d5e05e3f
--- /dev/null
+++ b/thunderbird-l10n/cy/localization/cy/messenger/viewSource.ftl
@@ -0,0 +1,19 @@
+# This Source Code Form is subject to the terms of the Mozilla Public
+# License, v. 2.0. If a copy of the MPL was not distributed with this
+# file, You can obtain one at http://mozilla.org/MPL/2.0/.
+
+context-text-action-find =
+    .label = Canfod
+    .accesskey = C
+
+context-text-action-find-again =
+    .label = Canfod Eto
+    .accesskey = C
+
+text-action-find =
+    .label = Canfod
+    .accesskey = C
+
+text-action-find-again =
+    .label = Canfod Eto
+    .accesskey = C
diff --git a/thunderbird-l10n/cy/localization/cy/security/certificates/certManager.ftl b/thunderbird-l10n/cy/localization/cy/security/certificates/certManager.ftl
new file mode 100644
index 0000000000..baed68d767
--- /dev/null
+++ b/thunderbird-l10n/cy/localization/cy/security/certificates/certManager.ftl
@@ -0,0 +1,228 @@
+# This Source Code Form is subject to the terms of the Mozilla Public
+# License, v. 2.0. If a copy of the MPL was not distributed with this
+# file, You can obtain one at http://mozilla.org/MPL/2.0/.
+
+certmgr-title =
+    .title = Rheolwr Tystysgrifau
+
+certmgr-tab-mine =
+    .label = Eich Tystysgrifau
+
+certmgr-tab-remembered =
+    .label = Penderfyniadau Dilysu
+
+certmgr-tab-people =
+    .label = Pobl
+
+certmgr-tab-servers =
+    .label = Gweinyddion
+
+certmgr-tab-ca =
+    .label = Awdurdodau
+
+certmgr-mine = Mae gennych dystysgrifau gan y cyrff hyn sy'n eich adnabod chi
+certmgr-remembered = Mae'r tystysgrifau hyn yn cael eu defnyddio i'ch adnabod chi ar wefannau
+certmgr-people = Mae gennych dystysgrifau ar ffeil sy'n adnabod y bobl hyn
+certmgr-server = Mae'r cofnodion hyn yn nodi eithriadau gwall tystysgrif gweinydd
+certmgr-ca = Mae gennych dystysgrifau ar ffeil sy'n adnabod yr awdurdodau tystysgrif
+
+certmgr-edit-ca-cert2 =
+    .title = Golygu gosodiadau ymddiried tystysgrif CA
+    .style = min-width: 48em;
+
+certmgr-edit-cert-edit-trust = Golygu gosodiadau ymddiried:
+
+certmgr-edit-cert-trust-ssl =
+    .label = Mae'r dystysgrif yn medru adnabod gwefannau.
+
+certmgr-edit-cert-trust-email =
+    .label = Mae'r dystysgrif yn medru adnabod defnyddwyr e-bost.
+
+certmgr-delete-cert2 =
+    .title = Dileu Tystysgrif
+    .style = min-width: 48em; min-height: 24em;
+
+certmgr-cert-host =
+    .label = Gwesteiwr
+
+certmgr-cert-name =
+    .label = Enw'r Dystysgrif
+
+certmgr-cert-server =
+    .label = Gweinydd
+
+certmgr-token-name =
+    .label = Dyfais Diogelwch
+
+certmgr-begins-label =
+    .label = Cychwyn ar
+
+certmgr-expires-label =
+    .label = Daw i ben ar
+
+certmgr-email =
+    .label = Cyfeiriad E-bost
+
+certmgr-serial =
+    .label = Rhif Cyfresol
+
+certmgr-fingerprint-sha-256 =
+    .label = Bysbrint SHA-256
+
+certmgr-view =
+    .label = Golwg…
+    .accesskey = G
+
+certmgr-edit =
+    .label = Golygu'r Ymddiriedaeth…
+    .accesskey = Y
+
+certmgr-export =
+    .label = Allforio…
+    .accesskey = A
+
+certmgr-delete =
+    .label = Dileu…
+    .accesskey = D
+
+certmgr-delete-builtin =
+    .label = Dileu neu Ddrwgdybio…
+    .accesskey = i
+
+certmgr-backup =
+    .label = Wrth Gefn…
+    .accesskey = W
+
+certmgr-backup-all =
+    .label = Popeth Wrth Gefn…
+    .accesskey = P
+
+certmgr-restore =
+    .label = Mewnforio…
+    .accesskey = M
+
+certmgr-add-exception =
+    .label = Ychwanegu Eithriad…
+    .accesskey = Y
+
+exception-mgr =
+    .title = Ychwanegu Eithriad Diogelwch
+
+exception-mgr-extra-button =
+    .label = Cadarnhau Eithriad Diogelwch
+    .accesskey = C
+
+exception-mgr-supplemental-warning = Ni fydd banciau, siopau a gwefannau cyhoeddus yn gofyn i chi wneud hyn.
+
+exception-mgr-cert-location-url =
+    .value = Lleoliad:
+
+exception-mgr-cert-location-download =
+    .label = Estyn Tystysgrif
+    .accesskey = G
+
+exception-mgr-cert-status-view-cert =
+    .label = Golwg…
+    .accesskey = G
+
+exception-mgr-permanent =
+    .label = Cadw'r estyniad yn barhaol
+    .accesskey = C
+
+pk11-bad-password = Cyfrinair yn anghywir.
+pkcs12-decode-err = Methu dadgodio'r ffeil.  Un ai nid yw mewn fformat PKCS#12, neu mae wedi ei lygru, neu roedd eich cyfrinair yn anghywir.
+pkcs12-unknown-err-restore = Methwyd ag adfer ffeil PKCS#12 am resymau anhysbys.
+pkcs12-unknown-err-backup = Methwyd â gwneud copi wrth gefn o'r ffeil PKCS#12 am resymau anhysbys.
+pkcs12-unknown-err = Methodd gweithrediad PKCS #12 am reswm anhysbys.
+pkcs12-info-no-smartcard-backup = Nid yw'n bosibl cadw tystysgrif wrth gefn o ddyfeisiadau caledwedd diogelwch megis cerdyn cof.
+pkcs12-dup-data = Mae'r dystysgrif a'r allwedd breifat yn bodoli eisoes ar y ddyfais diogelwch.
+
+## PKCS#12 file dialogs
+
+choose-p12-backup-file-dialog = Enw Ffeil i'w Gadw wrth Gefn
+file-browse-pkcs12-spec = Ffeiliau PKCS12
+choose-p12-restore-file-dialog = Ffeil Tystysgrif i'w Mewnforio
+
+## Import certificate(s) file dialog
+
+file-browse-certificate-spec = Ffeiliau Tystysgrif
+import-ca-certs-prompt = Dewis Ffeil yn cynnwys tystysgrif(au) CA i'w mewnforio
+import-email-cert-prompt = Dewis Ffeil yn cynnwys tystysgrif e-bost rhywun i'w fewnforio
+
+## For editing certificates trust
+
+# Variables:
+#   $certName: the name of certificate
+edit-trust-ca = Mae Tystysgrif "{ $certName }" yn cynrychioli Awdurdod Tystysgrifo.
+
+## For Deleting Certificates
+
+delete-user-cert-title =
+    .title = Dileu eich Tystysgrifau
+delete-user-cert-confirm = Ydych chi'n siŵr eich bod eisiau dileu'r tystysgrifau hyn?
+delete-user-cert-impact = Os byddwch yn dileu un o'ch tystysgrifau eich hun, nid oes modd ei ddefnyddio i adnabod eich hun.
+
+
+delete-ssl-override-title =
+    .title = Dileu Eithriad Tystysgrif Gweinydd
+delete-ssl-override-confirm = Ydych chi'n siŵr eich bod eisiau dileu eithriadau'r gweinydd?
+delete-ssl-override-impact = Os ydych yn dileu eithriad gweinydd, gallwch adfer gwirio diogelwch y gweinydd a disgwyl iddo ddefnyddio tystysgrif ddilys.
+
+delete-ca-cert-title =
+    .title = Dileu neu Ddadymddiried Tystysgrifau CA
+delete-ca-cert-confirm = Rydych wedi gofyn i gael dileu'r tystysgrifau TA hyn. Ar gyfer tystysgrifau mewnol bydd yr ymddiriedaeth yn cael ei dynnu, sydd a'r un effaith. Ydych chi'n siŵr eich bod eisiau dileu neu dad-ymddiried?
+delete-ca-cert-impact = Os fyddwch yn dileu neu dad-ymddiried tystysgrif awdurdod tystysgrifo (CA), ni fydd y rhaglen yn ymddiried unrhyw dystysgrif sy'n cael ei chyhoeddi gan y CA.
+
+
+delete-email-cert-title =
+    .title = Dileu Tystysgrifau E-bost
+delete-email-cert-confirm = Ydych chi'n siŵr eich bod eisiau dileu tystysgrifau e-bost y bobl hyn?
+delete-email-cert-impact = Os fyddwch yn dileu tystysgrif e-bost y person, ni fyddwch yn gallu anfon e-byst amgryptiedig at y person hwnnw.
+
+# Used for semi-uniquely representing a cert.
+#
+# Variables:
+#   $serialNumber : the serial number of the cert in AA:BB:CC hex format.
+cert-with-serial =
+    .value = Tystysgrif gyda rhif cyfresol : { $serialNumber }
+
+# Used to indicate that the user chose not to send a client authentication certificate to a server that requested one in a TLS handshake.
+send-no-client-certificate = Anfonwyd dim tystysgrif cleient
+
+# Used when no cert is stored for an override
+no-cert-stored-for-override = (Heb ei Storio)
+
+# When a certificate is unavailable (for example, it has been deleted or the token it exists on has been removed).
+certificate-not-available = (Dim ar gael)
+
+## Used to show whether an override is temporary or permanent
+
+permanent-override = Parhaol
+temporary-override = Dros dro
+
+## Add Security Exception dialog
+
+add-exception-branded-warning = Rydych ar fin atal y ffordd mae { -brand-short-name } yn adnabod y wefan.
+add-exception-invalid-header = Mae'r wefan yn ceisio dweud pwy ydyw gyda gwybodaeth annilys.
+add-exception-domain-mismatch-short = Gwefan Anghywir
+add-exception-domain-mismatch-long = Mae'r dystysgrif yn perthyn i wefan gwahanol, sy'n golygu y gall rhywun fod yn efelychu'r wefan hon.
+add-exception-expired-short = Hen Wybodaeth
+add-exception-expired-long = Nid yw'r dystysgrif yn ddilys ar hyn o bryd. Gall ei fod wedi cael ei ddwyn neu ei golli, a gall fod yn cael ei ddefnyddio i ymddangos fel y wefan hon.
+add-exception-unverified-or-bad-signature-short = Hunaniaeth Anhysbys
+add-exception-unverified-or-bad-signature-long = Methu ymddiried yn y dystysgrif am nad yw wedi ei ddilysu gan awdurdod hysbys sy'n defnyddio llofnod diogel.
+add-exception-valid-short = Tystysgrif Dilys
+add-exception-valid-long = Mae'r wefan yn darparu gwybodaeth ddilys amdani ei hun.  Nid oes angen gosod eithriad.
+add-exception-checking-short = Gwirio Gwybodaeth
+add-exception-checking-long = Ceisio adnabod y wefan…
+add-exception-no-cert-short = Dim Gwybodaeth ar Gael
+add-exception-no-cert-long = Methu canfod statws dynodiad ar gyfer y wefan hon.
+
+## Certificate export "Save as" and error dialogs
+
+save-cert-as = Cadw Tystysgrif i Ffeil
+cert-format-base64 = Tystysgrif X.509 (PEM)
+cert-format-base64-chain = Tystysgrif X.509gyda chadwyn (PEM)
+cert-format-der = Tystysgrif X.509 (DER)
+cert-format-pkcs7 = Tystysgrif X.509 (PKCS#7)
+cert-format-pkcs7-chain = Tystysgrif X.509 gyda chadwyn (PKCS#7)
+write-file-failure = Gwall Ffeil
diff --git a/thunderbird-l10n/cy/localization/cy/security/certificates/deviceManager.ftl b/thunderbird-l10n/cy/localization/cy/security/certificates/deviceManager.ftl
new file mode 100644
index 0000000000..433d904151
--- /dev/null
+++ b/thunderbird-l10n/cy/localization/cy/security/certificates/deviceManager.ftl
@@ -0,0 +1,133 @@
+# This Source Code Form is subject to the terms of the Mozilla Public
+# License, v. 2.0. If a copy of the MPL was not distributed with this
+# file, You can obtain one at http://mozilla.org/MPL/2.0/.
+
+
+## Strings used for device manager
+
+devmgr-window =
+    .title = Rheolwr Dyfeisiadau
+    .style = min-width: 67em; min-height: 32em;
+
+devmgr-devlist =
+    .label = Modiwlau a Dyfeisiadau Diogelwch
+
+devmgr-header-details =
+    .label = Manylion
+
+devmgr-header-value =
+    .label = Gwerth
+
+devmgr-button-login =
+    .label = Mewngofnodi
+    .accesskey = M
+
+devmgr-button-logout =
+    .label = Allgofnodi
+    .accesskey = A
+
+devmgr-button-changepw =
+    .label = Newid Cyfrinair
+    .accesskey = N
+
+devmgr-button-load =
+    .label = Llwytho
+    .accesskey = L
+
+devmgr-button-unload =
+    .label = Dadlwytho
+    .accesskey = D
+
+devmgr-button-enable-fips =
+    .label = Galluogi FIPS
+    .accesskey = F
+
+devmgr-button-disable-fips =
+    .label = Analluogi FIPS
+    .accesskey = F
+
+## Strings used for load device
+
+load-device =
+    .title = Llwytho Gyrrwr Dyfais PKCS#11
+
+load-device-info = Rhoi gwybodaeth am y modiwl rydych eisiau ei ychwanegu.
+
+load-device-modname =
+    .value = Enw Modiwl
+    .accesskey = M
+
+load-device-modname-default =
+    .value = Modiwl newydd PKCS#11
+
+load-device-filename =
+    .value = Enw ffeil modiwl
+    .accesskey = E
+
+load-device-browse =
+    .label = Pori…
+    .accesskey = P
+
+## Token Manager
+
+devinfo-status =
+    .label = Statws
+
+devinfo-status-disabled =
+    .label = Analluogwyd
+
+devinfo-status-not-present =
+    .label = Ddim yn Bresennol
+
+devinfo-status-uninitialized =
+    .label = Heb gychwyn
+
+devinfo-status-not-logged-in =
+    .label = Heb Fewngofnodi
+
+devinfo-status-logged-in =
+    .label = Wedi mewngofnodi
+
+devinfo-status-ready =
+    .label = Parod
+
+devinfo-desc =
+    .label = Disgrifiad
+
+devinfo-man-id =
+    .label = Gwneuthurwr
+
+devinfo-hwversion =
+    .label = Fersiwn HW
+devinfo-fwversion =
+    .label = Fersiwn FW
+
+devinfo-modname =
+    .label = Modiwl
+
+devinfo-modpath =
+    .label = Llwybr
+
+login-failed = Wedi methu Mewngofnodi
+
+devinfo-label =
+    .label = Label
+
+devinfo-serialnum =
+    .label = Rhif Cyfresol
+
+fips-nonempty-primary-password-required = Mae modd FIPS yn gofyn i chi gael Prif Gyfrinair wedi ei osod ar gyfer pob dyfais diogelwch. Rhowch gyfrinair cyn ceisio cychwyn modd FIPS.
+unable-to-toggle-fips = Methu newid modd FIPS ar gyfer y ddyfais diogelwch. Argymhellir eich bod yn gadael y rhaglen a'i hailgychwyn.
+load-pk11-module-file-picker-title = Dewis gyrrwr dyfais PKCS#11 i'w lwytho
+
+# Load Module Dialog
+load-module-help-empty-module-name =
+    .value = Nid oes modd i'r enw modiwl fod yn wag.
+
+# Do not translate 'Root Certs'
+load-module-help-root-certs-module-name =
+    .value = Mae ‘Root Certs‘ ar gadw ac nid oes modd ei ddefnyddio fel enw modiwl.
+
+add-module-failure = Methu ychwanegu modiwl
+del-module-warning = Ydych chi'n siŵr eich bod eisiau dileu'r modiwl diogelwch?
+del-module-error = Methu dileu modiwl
diff --git a/thunderbird-l10n/cy/localization/cy/security/pippki/pippki.ftl b/thunderbird-l10n/cy/localization/cy/security/pippki/pippki.ftl
new file mode 100644
index 0000000000..96441cb93e
--- /dev/null
+++ b/thunderbird-l10n/cy/localization/cy/security/pippki/pippki.ftl
@@ -0,0 +1,106 @@
+# This Source Code Form is subject to the terms of the Mozilla Public
+# License, v. 2.0. If a copy of the MPL was not distributed with this
+# file, You can obtain one at http://mozilla.org/MPL/2.0/.
+
+password-quality-meter = Mesurydd ansawdd y cyfrinair
+
+## Change Password dialog
+
+change-device-password-window =
+    .title = Newid Cyfrinair
+# Variables:
+# $tokenName (String) - Security device of the change password dialog
+change-password-token = Dyfais Diogelwch: { $tokenName }
+change-password-old = Cyfrinair cyfredol:
+change-password-new = Cyfrinair newydd:
+change-password-reenter = Y cyfrinair newydd (eto):
+pippki-failed-pw-change = Methu newid cyfrinair.
+pippki-incorrect-pw = Wedi rhoi cyfrinair anghywir. Ceisiwch eto.
+pippki-pw-change-ok = Mae'r cyfrinair wedi ei newid yn llwyddiannus.
+pippki-pw-empty-warning = Fydd eich cyfrineiriau a'ch allweddi preifat wedi'u storio ddim yn cael eu gwarchod.
+pippki-pw-erased-ok = Rydych wedi dileu eich Prif Gyfrinair. { pippki-pw-empty-warning }
+pippki-pw-not-wanted = Rhybudd! Rydych wedi penderfynu peidio defnyddio Prif Gyfrinair. { pippki-pw-empty-warning }
+pippki-pw-change2empty-in-fips-mode = Rydych ym modd FIPS. Mae FIPS angen gyfrinair nad yw'n wag.
+
+## Reset Primary Password dialog
+
+reset-primary-password-window2 =
+    .title = Ailosod Prif Gyfrinair
+    .style = min-width: 40em
+reset-password-button-label =
+    .label = Ailosod
+reset-primary-password-text = Os byddwch yn ailosod eich Prif Gyfrinair, bydd eich cyfrineiriau gwe ac e-bost, data ffurflen, tystysgrifau personol ac allweddi preifat sydd wedi eu cadw'n cael eu colli. Ydych chi'n siŵr eich bod eisiau ailosod eich Prif Gyfrinair?
+pippki-reset-password-confirmation-title = Ailosod Prif Gyfrinair
+pippki-reset-password-confirmation-message = Mae eich Prif Gyfrinair wedi cael ei ail osod.
+
+## Downloading cert dialog
+
+download-cert-window2 =
+    .title = Llwytho Tystysgrifau i Lawr
+    .style = min-width: 46em
+download-cert-message = Rydych wedi cael cais i ymddiried mewn Awdurdod Tystysgrifo (CA) newydd.
+download-cert-trust-ssl =
+    .label = Ymddiried yn yr Awdurdod Tystysgrifo i adnabod gwefannau.
+download-cert-trust-email =
+    .label = Ymddiried yn yr Awdurdod Tystysgrifo i adnabod defnyddwyr e-bost.
+download-cert-message-desc = Cyn ymddiried mewn Awdurdod Tystysgrifo at unrhyw bwrpas, dylech archwilio ei dystysgrif a'i bolisi a chanllawiau (os yw ar gael).
+download-cert-view-cert =
+    .label = Golwg
+download-cert-view-text = Archwilio tystysgrif Awdurdod Tystysgrifo
+
+## Client Authorization Ask dialog
+
+
+## Client Authentication Ask dialog
+
+client-auth-window =
+    .title = Cais am Adnabod Defnyddiwr
+client-auth-site-description = Mae'r wefan yn gofyn i chi ddweud pwy ydych gyda thystysgrif diogelwch:
+client-auth-choose-cert = Dewiswch dystysgrif i'w chyflwyno fel adnabyddiaeth:
+client-auth-send-no-certificate =
+    .label = Peidio ag anfon tystysgrif
+# Variables:
+# $hostname (String) - The domain name of the site requesting the client authentication certificate
+client-auth-site-identification = Mae “{ $hostname }” wedi gofyn i chi adnabod eich hun gyda thystysgrif:
+client-auth-cert-details = Manylion y dystysgrif hon:
+# Variables:
+# $issuedTo (String) - The subject common name of the currently-selected client authentication certificate
+client-auth-cert-details-issued-to = Cyhoeddwyd i: { $issuedTo }
+# Variables:
+# $serialNumber (String) - The serial number of the certificate (hexadecimal of the form "AA:BB:...")
+client-auth-cert-details-serial-number = Rhif cyfresol: { $serialNumber }
+# Variables:
+# $notBefore (String) - The date before which the certificate is not valid (e.g. Apr 21, 2023, 1:47:53 PM UTC)
+# $notAfter (String) - The date after which the certificate is not valid
+client-auth-cert-details-validity-period = Yn ddilys o { $notBefore } hyd { $notAfter }
+# Variables:
+# $keyUsages (String) - A list of already-localized key usages for which the certificate may be used
+client-auth-cert-details-key-usages = Prif Ddefnydd: { $keyUsages }
+# Variables:
+# $emailAddresses (String) - A list of email addresses present in the certificate
+client-auth-cert-details-email-addresses = Cyfeiriadau e-bost: { $emailAddresses }
+# Variables:
+# $issuedBy (String) - The issuer common name of the certificate
+client-auth-cert-details-issued-by = Cyhoeddwyd gan: { $issuedBy }
+# Variables:
+# $storedOn (String) - The name of the token holding the certificate (for example, "OS Client Cert Token (Modern)")
+client-auth-cert-details-stored-on = Storiwyd ar: { $storedOn }
+client-auth-cert-remember-box =
+    .label = Cofio'r penderfyniad yma
+
+## Set password (p12) dialog
+
+set-password-window =
+    .title = Dewiswch Gyfrinair Tystysgrif wrth Gefn
+set-password-message = Bydd y cyfrinair tystysgrif wrth gefn yma'n amddiffyn y ffeil wrth gefn rydych ar fin ei greu.  Rhaid gosod y cyfrinair i barhau gyda'r ffeil wrth gefn.
+set-password-backup-pw =
+    .value = Cyfrinair y dystysgrif wrth gefn:
+set-password-repeat-backup-pw =
+    .value = Cyfrinair y dystysgrif wrth gefn (eto):
+set-password-reminder = Pwysig: Os byddwch yn anghofio eich cyfrinair diogelwch cludadwy, ni fydd modd i chi adfer y ffeil wrth gefn yma eto.  Cofnodwch hwn mewn man diogel.
+
+## Protected authentication alert
+
+# Variables:
+# $tokenName (String) - The name of the token to authenticate to (for example, "OS Client Cert Token (Modern)")
+protected-auth-alert = Dilyswch i'r tocyn “{ $tokenName }”. Mae sut i wneud hynny yn dibynnu ar y tocyn (er enghraifft, defnyddio darllenydd bysbrint neu roi cod gyda bysellbad).
diff --git a/thunderbird-l10n/cy/localization/cy/services/accounts.ftl b/thunderbird-l10n/cy/localization/cy/services/accounts.ftl
new file mode 100644
index 0000000000..c77738b816
--- /dev/null
+++ b/thunderbird-l10n/cy/localization/cy/services/accounts.ftl
@@ -0,0 +1,8 @@
+# This Source Code Form is subject to the terms of the Mozilla Public
+# License, v. 2.0. If a copy of the MPL was not distributed with this
+# file, You can obtain one at http://mozilla.org/MPL/2.0/.
+
+# Variables:
+#   $user (String): the user name (e.g. "Ed")
+#   $system (String): the operating system (e.g. "Android")
+account-client-name = { $user }'s { -brand-short-name } ar { $system }
diff --git a/thunderbird-l10n/cy/localization/cy/toolkit/about/aboutAbout.ftl b/thunderbird-l10n/cy/localization/cy/toolkit/about/aboutAbout.ftl
new file mode 100644
index 0000000000..9c93e1bcd7
--- /dev/null
+++ b/thunderbird-l10n/cy/localization/cy/toolkit/about/aboutAbout.ftl
@@ -0,0 +1,9 @@
+# This Source Code Form is subject to the terms of the Mozilla Public
+# License, v. 2.0. If a copy of the MPL was not distributed with this
+# file, You can obtain one at http://mozilla.org/MPL/2.0/.
+
+about-about-title = About About
+about-about-note =
+    Dyma restr o dudalennau “about” er hwylustod.<br/>
+    Gall rhai ohonynt fod yn ddryslyd. Mae rhai ar gyfer pwrpas canfod gwallau yn unig.<br/>
+    Ac mae rhai ar goll am fod angen llinyn ymholiad arnynt.
diff --git a/thunderbird-l10n/cy/localization/cy/toolkit/about/aboutAddons.ftl b/thunderbird-l10n/cy/localization/cy/toolkit/about/aboutAddons.ftl
new file mode 100644
index 0000000000..5e7ddc0e9d
--- /dev/null
+++ b/thunderbird-l10n/cy/localization/cy/toolkit/about/aboutAddons.ftl
@@ -0,0 +1,502 @@
+# This Source Code Form is subject to the terms of the Mozilla Public
+# License, v. 2.0. If a copy of the MPL was not distributed with this
+# file, You can obtain one at http://mozilla.org/MPL/2.0/.
+
+addons-page-title = Rheolwr Ychwanegion
+search-header =
+    .placeholder = Search addons.mozilla.org
+    .searchbuttonlabel = Chwilio
+
+## Variables
+##   $domain - Domain name where add-ons are available (e.g. addons.mozilla.org)
+
+list-empty-get-extensions-message = Cewch estyniadau a themâu yn <a data-l10n-name="get-extensions">{ $domain }</a>
+list-empty-get-dictionaries-message = Cael geiriaduron o <a data-l10n-name="get-extensions">{ $domain }</a>
+list-empty-get-language-packs-message = Cael pecynnau iaith o <a data-l10n-name="get-extensions">{ $domain }</a>
+
+##
+
+list-empty-installed =
+    .value = Nid oes gennych ychwanegion o'r math yma wedi eu gosod
+list-empty-available-updates =
+    .value = Heb ganfod diweddariadau
+list-empty-recent-updates =
+    .value = Nid ydych wedi diweddaru eich ychwanegion yn ddiweddar
+list-empty-find-updates =
+    .label = Gwirio am Ddiweddariadau
+list-empty-button =
+    .label = Darllen rhagor am ychwanegion
+help-button = Cefnogaeth Ychwanegion
+sidebar-help-button-title =
+    .title = Cefnogaeth Ychwanegion
+addons-settings-button = Gosodiadau { -brand-short-name }
+sidebar-settings-button-title =
+    .title = Gosodiadau { -brand-short-name }
+show-unsigned-extensions-button =
+    .label = Nid oedd modd dilysu rhai estyniadau
+show-all-extensions-button =
+    .label = Dangos pob estyniad
+detail-version =
+    .label = Fersiwn
+detail-last-updated =
+    .label = Diweddarwyd Diwethaf
+addon-detail-description-expand = Dangos rhagor
+addon-detail-description-collapse = Dangos llai
+detail-contributions-description = Mae datblygwr yr ychwanegyn yn gofyn eich bod yn cynorthwyo i gefnogi datblygiad drwy wneud cyfraniad bychan.
+detail-contributions-button = Cyfrannu
+    .title = Cyfrannwch i ddatblygiad yr ategyn hwn
+    .accesskey = C
+detail-update-type =
+    .value = Diweddariadau Awtomatig
+detail-update-default =
+    .label = Rhagosodiad
+    .tooltiptext = Gosod diweddariadau'n awtomatig os mai dyna yw'r rhagosodedig
+detail-update-automatic =
+    .label = Ymlaen
+    .tooltiptext = Gosod diweddariadau'n awtomatig
+detail-update-manual =
+    .label = Diffodd
+    .tooltiptext = Peidio gosod diweddariadau'n awtomatig
+# Used as a description for the option to allow or block an add-on in private windows.
+detail-private-browsing-label = Rhedeg mewn Ffenestri Preifat
+# Some add-ons may elect to not run in private windows by setting incognito: not_allowed in the manifest.  This
+# cannot be overridden by the user.
+detail-private-disallowed-label = Heb ei ganiatáu mewn Ffenestri Preifat
+detail-private-disallowed-description2 = Nid yw'r estyniad hwn yn rhedeg tra'n pori'n preifat. <a data-l10n-name="learn-more">Darllen rhagor</a>
+# Some special add-ons are privileged, run in private windows automatically, and this permission can't be revoked
+detail-private-required-label = Angen Mynediad at Ffenestri Preifat
+detail-private-required-description2 = Mae gan yr estyniad hwn fynediad i'ch gweithgareddau ar-lein wrth bori'n breifat. <a data-l10n-name="learn-more">Dysgu mwy</a>
+detail-private-browsing-on =
+    .label = Caniatáu
+    .tooltiptext = Caniatáu wrth Bori Preifat
+detail-private-browsing-off =
+    .label = Peidio â Chaniatáu
+    .tooltiptext = Analluogi mewn Pori Preifat
+detail-home =
+    .label = Tudalen Cartref
+detail-home-value =
+    .value = { detail-home.label }
+detail-repository =
+    .label = Proffil Ychwanegyn
+detail-repository-value =
+    .value = { detail-repository.label }
+detail-check-for-updates =
+    .label = Gwirio am Ddiweddariadau
+    .accesskey = G
+    .tooltiptext = Gwirio am ddiweddariad i'r ychwanegyn
+detail-show-preferences =
+    .label =
+        { PLATFORM() ->
+            [windows] Dewisiadau
+           *[other] Dewisiadau
+        }
+    .accesskey =
+        { PLATFORM() ->
+            [windows] D
+           *[other] e
+        }
+    .tooltiptext =
+        { PLATFORM() ->
+            [windows] Newid dewisiadau'r ychwanegyn
+           *[other] Newid dewisiadau'r ychwanegyn
+        }
+detail-rating =
+    .value = Graddio
+addon-restart-now =
+    .label = Ailgychwyn nawr
+disabled-unsigned-heading =
+    .value = Mae rhai ychwanegion wedi eu hanalluogi
+disabled-unsigned-description = Mae'r ychwanegion canlynol wedi eu dilysu i'w defnyddio yn { -brand-short-name }. Gallwch <label data-l10n-name="find-addons">canfod newidiadau</label> neu ofyn i'r datblygwr iddynt gael eu dilysu.
+disabled-unsigned-learn-more = Darllen rhagor am ein hymdrechion i'ch cadw'n ddiogel ar-lein.
+disabled-unsigned-devinfo = Gall ddatblygwyr sydd â diddordeb mewn dilysu eu hychwanegion barhau drwy ddarllen ein <label data-l10n-name="learn-more">canllawiau</label>.
+plugin-deprecation-description = Rhywbeth ar goll? Nid yw rhai ategion yn cael eu cynnal bellach gan { -brand-short-name }. <label data-l10n-name="learn-more">Darllen Rhagor.</label>
+legacy-warning-show-legacy = Dangos hen estyniadau
+legacy-extensions =
+    .value = Hen Estyniadau
+legacy-extensions-description = Nid yw'r estyniadau hyn yn cyrraedd safonau cyfredol { -brand-short-name } ac mae nhw wedi cael eu diffodd. <label data-l10n-name="legacy-learn-more">Dysgu am y newidiadau i ychwanegion</label>
+private-browsing-description2 =
+    Mae { -brand-short-name } yn newid sut mae estyniadau'n gweithio o fewn pori preifat. Ni fydd unrhyw estyniadau newydd y byddwch chi'n eu hychwanegu at { -brand-short-name } yn rhedeg yn ragosodedig o fewn Ffenestri Prefat. Oni bai eich bod yn ei ganiatáu yn y gosodiadau, ni fydd estyniad yn gweithio wrth bori'n preifat, ac ni chaiff fynediad at eich gweithgareddau ar-lein yno. Rydym wedi gwneud y newid hwn i gadw eich pori preifat yn breifat.
+    <label data-l10n-name="private-browsing-learn-more">Dysgu sut i reoli gosodiadau estyniad.</label>
+addon-category-discover = Argymhellion
+addon-category-discover-title =
+    .title = Argymhellion
+addon-category-extension = Estyniadau
+addon-category-extension-title =
+    .title = Estyniadau
+addon-category-theme = Themâu
+addon-category-theme-title =
+    .title = Themâu
+addon-category-plugin = Ategion
+addon-category-plugin-title =
+    .title = Ategion
+addon-category-dictionary = Geiriaduron
+addon-category-dictionary-title =
+    .title = Geiriaduron
+addon-category-locale = Iaith
+addon-category-locale-title =
+    .title = Iaith
+addon-category-available-updates = Diweddariadau ar Gael
+addon-category-available-updates-title =
+    .title = Diweddariadau ar Gael
+addon-category-recent-updates = Diweddariadau Diweddar
+addon-category-recent-updates-title =
+    .title = Diweddariadau Diweddar
+addon-category-sitepermission = Caniatâd Gwefan
+addon-category-sitepermission-title =
+    .title = Caniatâd Gwefan
+# String displayed in about:addons in the Site Permissions section
+# Variables:
+#  $host (string) - DNS host name for which the webextension enables permissions
+addon-sitepermission-host = Caniatâd Gwefan { $host }
+
+## These are global warnings
+
+extensions-warning-safe-mode = Mae pob ychwanegyn wedi eu hanalluogi gan y modd diogel.
+extensions-warning-check-compatibility = Mae gwirio cydnawsedd ychwanegion wedi ei analluogi. Efallai fod gennych ychwanegion anghydnaws.
+extensions-warning-safe-mode2 =
+    .message = Mae pob ychwanegyn wedi eu hanalluogi gan y modd diogel.
+extensions-warning-check-compatibility2 =
+    .message = Mae gwirio cydnawsedd ychwanegion wedi ei analluogi. Efallai fod gennych ychwanegion anghydnaws.
+extensions-warning-check-compatibility-button = Galluogi
+    .title = Galluogi gwirio cydnawsedd ychwanegion
+extensions-warning-update-security = Mae gwirio diogelwch diweddariad wedi ei analluogi. Efallai eich bod o dan fygythiad gan ddiweddariad.
+extensions-warning-update-security2 =
+    .message = Mae gwirio diogelwch diweddariad wedi ei analluogi. Efallai eich bod o dan fygythiad gan ddiweddariad.
+extensions-warning-update-security-button = Galluogi
+    .title = Galluogi gwirio diogelwch diweddariad ychwanegyn
+extensions-warning-imported-addons2 =
+    .message = Gorffennwch osod yr estyniadau a fewnforiwyd i { -brand-short-name }.
+extensions-warning-imported-addons-button = Gosod Estyniadau
+
+## Strings connected to add-on updates
+
+addon-updates-check-for-updates = Gwirio am Ddiweddariadau
+    .accesskey = G
+addon-updates-view-updates = Gweld Diweddariadau Diweddar
+    .accesskey = D
+
+# This menu item is a checkbox that toggles the default global behavior for
+# add-on update checking.
+
+addon-updates-update-addons-automatically = Diweddaru Ychwanegion yn Awtomatig
+    .accesskey = A
+
+## Specific add-ons can have custom update checking behaviors ("Manually",
+## "Automatically", "Use default global behavior"). These menu items reset the
+## update checking behavior for all add-ons to the default global behavior
+## (which itself is either "Automatically" or "Manually", controlled by the
+## extensions-updates-update-addons-automatically.label menu item).
+
+addon-updates-reset-updates-to-automatic = Ailosod Pob Ychwanegyn i'w Diweddaru'n Awtomatig
+    .accesskey = P
+addon-updates-reset-updates-to-manual = Ailosod Pob Ychwanegyn i Ddiweddaru gyda Llaw
+    .accesskey = L
+
+## Status messages displayed when updating add-ons
+
+addon-updates-updating = Diweddaru ychwanegion
+addon-updates-installed = Mae eich ychwanegion wedi eu diweddaru.
+addon-updates-none-found = Heb ganfod diweddariadau
+addon-updates-manual-updates-found = Gweld Diweddariadau ar Gael
+
+## Add-on install/debug strings for page options menu
+
+addon-install-from-file = Gosod Ychwanegyn o Ffeil…
+    .accesskey = G
+addon-install-from-file-dialog-title = Dewis ategyn i'w osod
+addon-install-from-file-filter-name = Ychwanegion
+addon-open-about-debugging = Dadfygio Ychwanegion
+    .accesskey = Y
+
+## Extension shortcut management
+
+# This is displayed in the page options menu
+addon-manage-extensions-shortcuts = Rheoli Estyniad Llwybrau Byr
+    .accesskey = R
+shortcuts-no-addons = Nid oes gennych unrhyw estyniadau wedi'u galluogi.
+shortcuts-no-commands = Nid oes gan yr estyniadau canlynol lwybrau byr:
+shortcuts-input =
+    .placeholder = Teipiwch llwybr byr
+shortcuts-browserAction2 = Cychwyn botwm bar offer
+shortcuts-pageAction = Cychwyn gweithred tudalen
+shortcuts-sidebarAction = Toglo'r bar ochr
+shortcuts-modifier-mac = Cynnwys Ctrl, Alt, neu ⌘
+shortcuts-modifier-other = Cynnwys Ctrl neu Alt
+shortcuts-invalid = Cyfuniad annilys
+shortcuts-letter = Teipiwch lythyr
+shortcuts-system = Methu anwybyddu llwybr byr { -brand-short-name }
+# String displayed in warning label when there is a duplicate shortcut
+shortcuts-duplicate = Llwybr byr dyblyg
+# String displayed when a keyboard shortcut is already assigned to more than one add-on
+# Variables:
+#   $shortcut (string) - Shortcut string for the add-on
+shortcuts-duplicate-warning-message = Mae { $shortcut } yn cael ei ddefnyddio fel llwybr byr mewn mwy nag un achos. Gall llwybrau byr dyblyg achosi ymddygiad annisgwyl.
+# String displayed when a keyboard shortcut is already assigned to more than one add-on
+# Variables:
+#   $shortcut (string) - Shortcut string for the add-on
+shortcuts-duplicate-warning-message2 =
+    .message = Mae { $shortcut } yn cael ei ddefnyddio fel llwybr byr mewn mwy nag un achos. Gall llwybrau byr dyblyg achosi ymddygiad annisgwyl.
+# String displayed when a keyboard shortcut is already used by another add-on
+# Variables:
+#   $addon (string) - Name of the add-on
+shortcuts-exists = Ar waith eisoes gan { $addon }
+# Variables:
+#   $numberToShow (number) - Number of other elements available to show
+shortcuts-card-expand-button =
+    { $numberToShow ->
+        [zero] Dangos { $numberToShow } yn Rhagor
+        [one] Dangos { $numberToShow } yn Rhagor
+        [two] Dangos { $numberToShow } yn Rhagor
+        [few] Dangos { $numberToShow } yn Rhagor
+        [many] Dangos { $numberToShow } yn Rhagor
+       *[other] Dangos { $numberToShow } yn Rhagor
+    }
+shortcuts-card-collapse-button = Dangos Llai
+header-back-button =
+    .title = Mynd nôl
+
+## Recommended add-ons page
+
+# Explanatory introduction to the list of recommended add-ons. The action word
+# ("recommends") in the final sentence is a link to external documentation.
+discopane-intro =
+    Mae estyniadau a themâu yn debyg i apiau ar gyfer eich porwr, ac maen nhw'n gadael i chi
+    diogelu cyfrineiriau, llwytho fideos i lawr, dod o hyd i gytundebau, rhwystro hysbysebion blin, newid
+    golwg eich porwr a llawer mwy. Mae'r rhaglenni meddalwedd bach hyn fel arfer yn cael eu datblygu gan drydydd parti. Dyma detholiad y mae { -brand-product-name }<a data-l10n-name="learn-more-trigger">
+    yn eu hargymell </a> am ddiogelwch, perfformiad, a swyddogaethau gwell.
+# Notice to make user aware that the recommendations are personalized.
+discopane-notice-recommendations =
+    Mae rhai o'r argymhellion hyn wedi'u dewis yn benodol ar eich cyfer chi. Maen nhw'n seiliedig ar 
+    estyniadau eraill rydych chi wedi'u gosod, eich proffil dewisiadau, a'ch ystadegau defnydd.
+# Notice to make user aware that the recommendations are personalized.
+discopane-notice-recommendations2 =
+    .message =
+        Mae rhai o'r argymhellion hyn wedi'u dewis yn benodol ar eich cyfer chi. Maen nhw'n seiliedig ar 
+        estyniadau eraill rydych chi wedi'u gosod, eich proffil dewisiadau, a'ch ystadegau defnydd.
+discopane-notice-learn-more = Darllen rhagor
+privacy-policy = Polisi Preifatrwydd
+# Refers to the author of an add-on, shown below the name of the add-on.
+# Variables:
+#   $author (string) - The name of the add-on developer.
+created-by-author = gan <a data-l10n-name="author">{ $author }</a>
+# Shows the number of daily users of the add-on.
+# Variables:
+#   $dailyUsers (number) - The number of daily users.
+user-count = Defnyddwyr: { $dailyUsers }
+install-extension-button = Ychwanegu at { -brand-product-name }
+install-theme-button = Gosod Thema
+# The label of the button that appears after installing an add-on. Upon click,
+# the detailed add-on view is opened, from where the add-on can be managed.
+manage-addon-button = Rheoli
+find-more-addons = Canfod rhagor o ychwanegion
+find-more-themes = Canfod themâu eraill
+# This is a label for the button to open the "more options" menu, it is only
+# used for screen readers.
+addon-options-button =
+    .aria-label = Rhagor o Ddewisiadau
+
+## Add-on actions
+
+report-addon-button = Adrodd
+remove-addon-button = Tynnu
+# The link will always be shown after the other text.
+remove-addon-disabled-button = Methu ei Dynnu <a data-l10n-name="link"> Pam? </a>
+disable-addon-button = Analluogi
+enable-addon-button = Galluogi
+# This is used for the toggle on the extension card, it's a checkbox and this
+# is always its label.
+extension-enable-addon-button-label =
+    .aria-label = Galluogi
+preferences-addon-button =
+    { PLATFORM() ->
+        [windows] Opsiynau
+       *[other] Dewisiadau
+    }
+details-addon-button = Manylion
+release-notes-addon-button = Nodiadau Rhyddhau
+permissions-addon-button = Caniatâd
+extension-enabled-heading = Galluogwyd
+extension-disabled-heading = Analluogwyd
+theme-enabled-heading = Galluogwyd
+theme-disabled-heading2 = Themâu wedi'u Cadw
+plugin-enabled-heading = Galluogwyd
+plugin-disabled-heading = Analluogwyd
+dictionary-enabled-heading = Galluogwyd
+dictionary-disabled-heading = Analluogwyd
+locale-enabled-heading = Galluogwyd
+locale-disabled-heading = Analluogwyd
+sitepermission-enabled-heading = Galluogwyd
+sitepermission-disabled-heading = Analluogwyd
+always-activate-button = Gweithredu Bob Tro
+never-activate-button = Byth Gweithredu
+addon-detail-author-label = Awdur
+addon-detail-version-label = Fersiwn
+addon-detail-last-updated-label = Diweddarwyd Diwethaf
+addon-detail-homepage-label = Tudalen Cartref
+addon-detail-rating-label = Graddio
+# Message for add-ons with a staged pending update.
+install-postponed-message = Bydd yr estyniad hwn yn cael ei ddiweddaru pan fydd { -brand-short-name } yn ailgychwyn.
+# Message for add-ons with a staged pending update.
+install-postponed-message2 =
+    .message = Bydd yr estyniad hwn yn cael ei ddiweddaru pan fydd { -brand-short-name } yn ailgychwyn.
+install-postponed-button = Diweddaru Nawr
+# The average rating that the add-on has received.
+# Variables:
+#   $rating (number) - A number between 0 and 5. The translation should show at most one digit after the comma.
+five-star-rating =
+    .title = Graddiwyd { NUMBER($rating, maximumFractionDigits: 1) } allan o 5
+# This string is used to show that an add-on is disabled.
+# Variables:
+#   $name (string) - The name of the add-on
+addon-name-disabled = { $name } (analluogwyd)
+# The number of reviews that an add-on has received on AMO.
+# Variables:
+#   $numberOfReviews (number) - The number of reviews received
+addon-detail-reviews-link =
+    { $numberOfReviews ->
+        [zero] { $numberOfReviews } adolygiad
+        [one] { $numberOfReviews } adolygiad
+        [two] { $numberOfReviews } adolygiad
+        [few] { $numberOfReviews } adolygiad
+        [many] { $numberOfReviews } adolygiad
+       *[other] { $numberOfReviews } adolygiad
+    }
+
+## Pending uninstall message bar
+
+# Variables:
+#   $addon (string) - Name of the add-on
+pending-uninstall-description = Mae <span data-l10n-name="addon-name">{ $addon }</span> wedi ei dynnu.
+# Variables:
+#   $addon (string) - Name of the add-on
+pending-uninstall-description2 =
+    .message = Mae { $addon } wedi ei dynnu.
+pending-uninstall-undo-button = Dadwneud
+addon-detail-updates-label = Caniatáu diweddariadau awtomatig
+addon-detail-updates-radio-default = Rhagosodiad
+addon-detail-updates-radio-on = Ymlaen
+addon-detail-updates-radio-off = Diffodd
+addon-detail-update-check-label = Gwirio am Ddiweddariadau
+install-update-button = Diweddaru
+# aria-label associated to the updates row to help screen readers to announce the group
+# of input controls being entered.
+addon-detail-group-label-updates =
+    .aria-label = { addon-detail-updates-label }
+# This is the tooltip text for the private browsing badge in about:addons. The
+# badge is the private browsing icon included next to the extension's name.
+addon-badge-private-browsing-allowed2 =
+    .title = Caniatáu mewn ffenestri preifat
+    .aria-label = { addon-badge-private-browsing-allowed2.title }
+addon-detail-private-browsing-help = Pan mae'n cael ei ganiatáu, bydd yr estyniad ar gael i'ch gweithgareddau ar-lein tra byddwch yn pori'n breifat. <a data-l10n-name="learn-more"> Gwybod rhagor</a>
+addon-detail-private-browsing-allow = Caniatáu
+addon-detail-private-browsing-disallow = Peidio â Chaniatáu
+# aria-label associated to the private browsing row to help screen readers to announce the group
+# of input controls being entered.
+addon-detail-group-label-private-browsing =
+    .aria-label = { detail-private-browsing-label }
+
+## "sites with restrictions" (internally called "quarantined") are special domains
+## where add-ons are normally blocked for security reasons.
+
+# Used as a description for the option to allow or block an add-on on quarantined domains.
+addon-detail-quarantined-domains-label = Rhedeg ar wefannau gyda chyfyngiadau
+# Used as help text part of the quarantined domains UI controls row.
+addon-detail-quarantined-domains-help = Pan yn cael ei ganiatáu, bydd gan yr estyniad fynediad i wefannau sy'n cael eu cyfyngu gan { -vendor-short-name }. Caniatewch dim ond os ydych chi'n ymddiried yn yr estyniad hwn.
+# Used as label and tooltip text on the radio inputs associated to the quarantined domains UI controls.
+addon-detail-quarantined-domains-allow = Caniatáu
+addon-detail-quarantined-domains-disallow = Peidio Caniatáu
+# aria-label associated to the quarantined domains exempt row to help screen readers to announce the group.
+addon-detail-group-label-quarantined-domains =
+    .aria-label = { addon-detail-quarantined-domains-label }
+
+## This is the tooltip text for the recommended badges for an extension in about:addons. The
+## badge is a small icon displayed next to an extension when it is recommended on AMO.
+
+addon-badge-recommended2 =
+    .title = Dim ond estyniadau sy'n cwrdd â'n safonau ar gyfer diogelwch a pherfformiad y mae { -brand-product-name } yn eu hargymell
+    .aria-label = { addon-badge-recommended2.title }
+# We hard code "Mozilla" in the string below because the extensions are built
+# by Mozilla and we don't want forks to display "by Fork".
+addon-badge-line3 =
+    .title = Estyniad swyddogol wedi'i adeiladu gan Mozilla. Mae'n cydfynd â safonau diogelwch a pherfformiad
+    .aria-label = { addon-badge-line3.title }
+addon-badge-verified2 =
+    .title = Mae'r estyniad hwn wedi'i adolygu i fodloni ein safonau ar gyfer diogelwch a pherfformiad
+    .aria-label = { addon-badge-verified2.title }
+
+##
+
+available-updates-heading = Diweddariadau ar Gael
+recent-updates-heading = Diweddariadau Diweddar
+release-notes-loading = Yn llwytho…
+release-notes-error = Ymddiheuriadau ond bu gwall llwytho'r nodiadau ryddhau.
+addon-permissions-empty = Nid oes angen unrhyw ganiatâd ar yr estyniad hwn
+addon-permissions-required = Caniatâd angenrheidiol y swyddogaethau craidd:
+addon-permissions-optional = Caniatâd dewisol ar gyfer y swyddogaethau ychwanegol:
+addon-permissions-learnmore = Darllen rhagor am ganiatâd
+recommended-extensions-heading = Estyniadau Cymeradwy
+recommended-themes-heading = Themâu Cymeradwy
+# Variables:
+#   $hostname (string) - Host where the permissions are granted
+addon-sitepermissions-required = Yn caniatáu'r galluoedd canlynol i <span data-l10n-name="hostname">{ $hostname }</span>:
+# A recommendation for the Firefox Color theme shown at the bottom of the theme
+# list view. The "Firefox Color" name itself should not be translated.
+recommended-theme-1 = Teimlo'n greadigol? <a data-l10n-name="link">Adeiladwch eich thema eich hun gyda Firefox Color. </a>
+
+## Page headings
+
+extension-heading = Rheoli eich estyniadau
+theme-heading = Rheoli eich themâu
+plugin-heading = Rheoli eich ategion
+dictionary-heading = Rheoli eich geiriaduron
+locale-heading = Rheoli eich ieithoedd
+updates-heading = Rheoli Eich Diweddariadau
+sitepermission-heading = Rheoli Eich Caniatâd Gwefan
+discover-heading = Personoli Eich { -brand-short-name }
+shortcuts-heading = Rheoli Estyniad Llwybrau Byr
+default-heading-search-label = Canfod rhagor o ychwanegion
+addons-heading-search-input =
+    .placeholder = Search addons.mozilla.org
+addon-page-options-button =
+    .title = Offer ar gyfer pob ychwanegyn
+
+## Detail notifications
+## Variables:
+##   $name (string) - Name of the add-on.
+
+# Variables:
+#   $version (string) - Application version.
+details-notification-incompatible = Mae { $name } yn anghydnaws â { -brand-short-name } { $version }.
+# Variables:
+#   $version (string) - Application version.
+details-notification-incompatible2 =
+    .message = Mae { $name } yn anghydnaws â { -brand-short-name } { $version }.
+details-notification-incompatible-link = Rhagor o Wybodaeth
+details-notification-unsigned-and-disabled = Nid oedd modd dilysu { $name } i'w ddefnyddio yn { -brand-short-name } ac mae wedi ei analluogi.
+details-notification-unsigned-and-disabled2 =
+    .message = Nid oedd modd dilysu { $name } i'w ddefnyddio yn { -brand-short-name } ac mae wedi ei analluogi.
+details-notification-unsigned-and-disabled-link = Rhagor o Wybodaeth
+details-notification-unsigned = Nid oedd modd dilysu { $name } i'w defnyddio yn { -brand-short-name }. Cymerwch ofal.
+details-notification-unsigned2 =
+    .message = Nid oedd modd dilysu { $name } i'w defnyddio yn { -brand-short-name }. Cymerwch ofal.
+details-notification-unsigned-link = Rhagor o Wybodaeth
+details-notification-blocked = Mae { $name } wedi ei analluogi o ganlyniad i faterion diogelwch a sefydlogrwydd.
+details-notification-blocked2 =
+    .message = Mae { $name } wedi ei analluogi o ganlyniad i faterion diogelwch a sefydlogrwydd.
+details-notification-blocked-link = Rhagor o Wybodaeth
+details-notification-softblocked = Mae'n hysbys fod { $name } yn achosi anawsterau diogelwch a sefydlogrwydd.
+details-notification-softblocked2 =
+    .message = Mae'n hysbys fod { $name } yn achosi anawsterau diogelwch a sefydlogrwydd.
+details-notification-softblocked-link = Rhagor o Wybodaeth
+details-notification-gmp-pending = Bydd { $name } yn cael ei osod yn fuan.
+details-notification-gmp-pending2 =
+    .message = Bydd { $name } yn cael ei osod yn fuan.
+
+## Gecko Media Plugins (GMPs)
+
+plugins-gmp-license-info = Manylion trwyddedu
+plugins-gmp-privacy-info = Manylion Preifatrwydd
+plugins-openh264-name = OpenH264 Video Codec wedi ei ddarparu gan Cisco Systems, Inc.
+plugins-openh264-description = Mae'r ategyn hwn yn cael ei osod yn awtomatig gan Mozilla er mwyn cyd-fynd â manyleb y WebRTC ac i alluogi galwadau WebRTC gyda dyfeisiau sydd angen y codec fideo H.264. Ewch i http://www.openh264.org/ i weld y cod ffynhonnell a darllen rhagor am ei ddefnyddio.
+plugins-widevine-name = Mae'r Widevine Content Decryption Module wedi ei ddarparu gan Google Inc.
+plugins-widevine-description = Mae'r ategyn hwn yn galluogi chwarae cyfryngau amgryptiedig yn unol â manyleb Estyniadau Cyfryngau Amgryptiedig. Fel rheol defnyddir cyfryngau wedi'i amgryptio gan wefannau i ddiogelu rhag copïo cynnwys cyfryngau premiwm. Ewch i https://www.w3.org/TR/encrypted-media/ am fwy o wybodaeth ar Estyniadau Cyfryngau Amgryptiedig.
diff --git a/thunderbird-l10n/cy/localization/cy/toolkit/about/aboutCompat.ftl b/thunderbird-l10n/cy/localization/cy/toolkit/about/aboutCompat.ftl
new file mode 100644
index 0000000000..9552cfd9f0
--- /dev/null
+++ b/thunderbird-l10n/cy/localization/cy/toolkit/about/aboutCompat.ftl
@@ -0,0 +1,24 @@
+# This Source Code Form is subject to the terms of the Mozilla Public
+# License, v. 2.0. If a copy of the MPL was not distributed with this
+# file, You can obtain one at http://mozilla.org/MPL/2.0/.
+
+label-disable = Analluogi
+label-enable = Galluogi
+label-interventions = Ymyriadau
+# Variables:
+#   $bug (string) - Bug number
+label-more-information = Rhagor o Wybodaeth: Byg { $bug }
+label-overrides = Tros reolaeth Asiant Defnyddiwr
+text-disabled-in-about-config = Mae'r nodwedd hon wedi ei analluogi yn about:config
+text-no-interventions = Nid oes ymyriadau yn cael eu defnyddio
+text-no-overrides = Nid oes unrhyw ymyriadau UA yn cael eu defnyddio
+text-title = about:compat
+
+## Do not translate "SmartBlock". For reference, SmartBlock is a feature
+## of Firefox anti-tracking which fixes website breakage caused when
+## trackers are blocked, by acting just enough like those trackers to fix the
+## breakage. SmartBlock also contains special fixes for sites broken by
+## Firefox's Total Cookie Protection feature.
+
+label-smartblock = Atgyweiriadau SmartBlock
+text-no-smartblock = Nid oes unrhyw atgyweiriadau SmartBlock yn cael eu defnyddio
diff --git a/thunderbird-l10n/cy/localization/cy/toolkit/about/aboutGlean.ftl b/thunderbird-l10n/cy/localization/cy/toolkit/about/aboutGlean.ftl
new file mode 100644
index 0000000000..b6f4240b50
--- /dev/null
+++ b/thunderbird-l10n/cy/localization/cy/toolkit/about/aboutGlean.ftl
@@ -0,0 +1,106 @@
+# This Source Code Form is subject to the terms of the Mozilla Public
+# License, v. 2.0. If a copy of the MPL was not distributed with this
+# file, You can obtain one at http://mozilla.org/MPL/2.0/.
+
+
+### "FOG", "Glean", and "Glean SDK" should remain in English.
+
+-fog-brand-name = FOG
+-glean-brand-name = Glean
+glean-sdk-brand-name = SDK { -glean-brand-name }
+glean-debug-ping-viewer-brand-name = Teclyn Dadfygio Pingiau { -glean-brand-name }
+about-glean-page-title2 = Ynghylch { -glean-brand-name }
+about-glean-header = Ynghylch { -glean-brand-name }
+about-glean-interface-description =
+    Mae <a data-l10n-name="glean-sdk-doc-link">{ glean-sdk-brand-name }</a>
+    yn lyfrgell casglu data sy'n cael ei ddefnyddio mewn projectau { -vendor-short-name }.
+    Mae'r rhyngwyneb hwn wedi'i gynllunio i'w ddefnyddio gan ddatblygwyr a phrofwyr <a data-l10n-name="fog-link">i brofi'r offeryniaeth</a> â llaw.
+about-glean-upload-enabled = Mae llwytho data i fyny wedi'i alluogi.
+about-glean-upload-disabled = Mae llwytho data i fyny wedi'i analluogi.
+about-glean-upload-enabled-local = Dim ond ar gyfer anfon i weinydd lleol y mae llwytho data i fyny wedi'i alluogi.
+about-glean-upload-fake-enabled =
+    Mae llwytho data i fyny wedi'i analluogi,
+    ond rydyn ni'n dweud celwydd ac yn dweud wrth y { glean-sdk-brand-name } ei fod wedi'i alluogi
+    fel bod data yn dal i gael ei gofnodi'n lleol.
+    Nodyn: Os ydych chi'n gosod tag dadfygio, bydd pingiau'n cael eu llwytho i fyny i'r
+    <a data-l10n-name="glean-debug-ping-viewer">{ glean-debug-ping-viewer-brand-name }</a> beth bynnag yw'r gosodiadau.
+# This message is followed by a bulleted list.
+about-glean-prefs-and-defines = Mae <a data-l10n-name="fog-prefs-and-defines-doc-link">dewisiadau a diffiniadau perthnasol</a> yn cynnwys:
+# Variables:
+#   $data-upload-pref-value (String): the value of the datareporting.healthreport.uploadEnabled pref. Typically "true", sometimes "false"
+# Do not translate strings between <code> </code> tags.
+about-glean-data-upload = <code>datareporting.healthreport.uploadEnabled</code>: { $data-upload-pref-value }
+# Variables:
+#   $local-port-pref-value (Integer): the value of the telemetry.fog.test.localhost_port pref. Typically 0. Can be negative.
+# Do not translate strings between <code> </code> tags.
+about-glean-local-port = <code>telemetry.fog.test.localhost_port</code>: { $local-port-pref-value }
+# Variables:
+#   $glean-android-define-value (Boolean): the value of the MOZ_GLEAN_ANDROID define. Typically "false", sometimes "true".
+# Do not translate strings between <code> </code> tags.
+about-glean-glean-android = <code>MOZ_GLEAN_ANDROID</code>: { $glean-android-define-value }
+# Variables:
+#   $moz-official-define-value (Boolean): the value of the MOZILLA_OFFICIAL define.
+# Do not translate strings between <code> </code> tags.
+about-glean-moz-official = <code>MOZILLA_OFFICIAL</code>: { $moz-official-define-value }
+about-glean-about-testing-header = Ynghylch Profi
+# This message is followed by a numbered list.
+about-glean-manual-testing =
+    Mae cyfarwyddiadau llawn wedi'u dogfennu yn y
+    <a data-l10n-name="fog-instrumentation-test-doc-link">{ -fog-brand-name } dogfennau profi'r offeryniaeth</a>
+    ac yn y <a data-l10n-name="glean-sdk-doc-link">{ glean-sdk-brand-name } ddogfennaeth</a>,
+    ond, yn fyr, i brofi â llaw bod eich offeryniaeth yn gweithio, dylech:
+# This message is an option in a dropdown filled with untranslated names of pings.
+about-glean-no-ping-label = (peidiwch â chyflwyno unrhyw pingiau)
+# An in-line text input field precedes this string.
+about-glean-label-for-tag-pings = Yn y maes blaenorol sicrhewch fod tag dadfygio cofiadwy fel y gallwch adnabod eich pingiau'n ddiweddarach.
+# An in-line text input field precedes this string.
+about-glean-label-for-tag-pings-with-requirements = Gosodwch dag dadfygio cofiadwy <span>(20 nod neu lai, alffaniwmerig a - yn unig)</span> er mwyn i chi allu adnabod eich pings yn nes ymlaen.
+# An in-line drop down list precedes this string.
+# Do not translate strings between <code> </code> tags.
+about-glean-label-for-ping-names =
+    Dewiswch o'r rhestr flaenorol y ping y mae eich offeryniaeth ynddo.
+    Os yw mewn <a data-l10n-name="custom-ping-link">custom-ping</a>, dewiswch yr un hwnnw.
+    Fel arall, y rhagosodiad ar gyfer metrigau <code>digwyddiad</code> yw
+    y  ping <code>digwyddiadau</code>
+    a'r rhagosodiad ar gyfer pob metrig arall yw
+    y ping <code>metrics</code>.
+# An in-line check box precedes this string.
+about-glean-label-for-log-pings =
+    (Dewisol. Ticiwch y blwch blaenorol os ydych am i pingiau gael eu cofnodi hefyd pan gânt eu cyflwyno.
+    Bydd angen i chi hefyd <a data-l10n-name="enable-logging-link">alluogi cofnodi</a>.)
+# Variables
+#   $debug-tag (String): The user-set value of the debug tag input on this page. Like "about-glean-kV"
+# An in-line button labeled "Apply settings and submit ping" precedes this string.
+about-glean-label-for-controls-submit =
+    Pwyswch y botwm blaenorol i dagio pob ping { -glean-brand-name } gyda'ch tag a chyflwynwch y ping a ddewiswyd.
+    (Bydd yr holl pingiau sy'n cael eu cyflwyno o hynny hyd nes y byddwch yn ailgychwyn y rhaglenyn cael eu tagio
+    <code>{ $debug-tag }</code>.)
+about-glean-li-for-visit-gdpv =
+    <a data-l10n-name="gdpv-tagged-pings-link">Ewch i dudalen { glean-debug-ping-viewer-brand-name } am bingiau gyda'ch tag</a>.
+    Dylai ddim cymryd mwy nag ychydig eiliadau o bwyso'r botwm i'ch ping gyrraedd.
+    Weithiau gall gymryd ychydig o funudau.
+# Do not translate strings between <code> </code> tags.
+about-glean-adhoc-explanation =
+    Am ragor o brofion <i>ad hoc</i>,
+    gallwch hefyd bennu gwerth cyfredol darn penodol o offeryniaeth
+    trwy agor consol devtools yma ar <code>about:glean</code>
+    a defnyddio'r API <code>testGetValue()</code> fel
+    <code>Glean.metricCategory.metricName.testGetValue()</code>.
+# Do not translate strings between <code> </code> tags.
+about-glean-adhoc-explanation2 =
+    Am ragor o brofion <i>ad hoc</i>,
+    gallwch hefyd bennu gwerth cyfredol darn penodol o offeryniaeth
+    trwy agor consol devtools yma ar <code>about:glean</code>
+    a defnyddio'r API <code>testGetValue()</code> fel
+    <code>Glean.metricCategory.metricName.testGetValue()</code>
+    ar gyfer metrig o'r enw <code>metric.category.metric_name</code>.
+# Do not translate strings between <code> </code> tags.
+about-glean-adhoc-note =
+    Sylwch eich bod yn defnyddio'r API Glean JS trwy ddefnyddio'r consol devtools.
+    Mae hyn yn golygu bod y categori metrig a'r enw metrig wedi'u fformatio
+    <code>camelCase</code> yn wahanol i'r APIs Rust a C++.
+controls-button-label-verbose = Gosod y gosodiadau ac anfon ping
+about-glean-about-data-header = Ynghylch Data
+about-glean-about-data-explanation =
+    I bori drwy'r rhestr o ddata a gasglwyd, edrychwch ar y
+    <a data-l10n-name="glean-dictionary-link"> { -glean-brand-name } Geiriadur</a>.
diff --git a/thunderbird-l10n/cy/localization/cy/toolkit/about/aboutHttpsOnlyError.ftl b/thunderbird-l10n/cy/localization/cy/toolkit/about/aboutHttpsOnlyError.ftl
new file mode 100644
index 0000000000..92c7ae6ff4
--- /dev/null
+++ b/thunderbird-l10n/cy/localization/cy/toolkit/about/aboutHttpsOnlyError.ftl
@@ -0,0 +1,24 @@
+# This Source Code Form is subject to the terms of the Mozilla Public
+# License, v. 2.0. If a copy of the MPL was not distributed with this
+# file, You can obtain one at http://mozilla.org/MPL/2.0/.
+
+about-httpsonly-title-alert = Rhybudd Modd HTTPS-yn-Unig
+about-httpsonly-title-site-not-available = Nid yw'r Safle Diogel ar Gael
+# Variables:
+#   $websiteUrl (String) - Url of the website that failed to load. Example: www.example.com
+about-httpsonly-explanation-unavailable2 = Rydych wedi galluogi'r Modd HTTPS-yn-Unig ar gyfer gwell diogelwch, ac nid oes fersiwn HTTPS o <em>{ $websiteUrl }</em> ar gael.
+about-httpsonly-explanation-question = Beth allai fod yn achosi hyn?
+about-httpsonly-explanation-nosupport = Yn fwyaf tebygol, nid yw'r wefan yn cefnogi HTTPS.
+about-httpsonly-explanation-risk = Mae hefyd yn bosibl bod ymosodwr yn ceisio ymyrryd. Os penderfynwch ymweld â'r wefan, peidiwch â rhannu unrhyw fanylion sensitif fel cyfrineiriau, e-byst, neu fanylion cardiau credyd.
+about-httpsonly-explanation-continue = Os byddwch yn parhau, bydd y Modd HTTPS-yn-Unig yn cael ei ddiffodd dros dro ar gyfer y wefan hon.
+about-httpsonly-button-continue-to-site = Ymlaen i'r Wefan HTTP
+about-httpsonly-button-go-back = Mynd Nôl
+about-httpsonly-link-learn-more = Darllen Rhagor…
+
+## Suggestion Box that only shows up if a secure connection to www can be established
+## Variables:
+##   $websiteUrl (String) - Url of the website that can be securely loaded with these alternatives. Example: example.com
+
+about-httpsonly-suggestion-box-header = Dewisiadau Arall Posib
+about-httpsonly-suggestion-box-www-text = Mae fersiwn ddiogel o <em>www{ $websiteUrl }</em>. Gallwch ymweld â'r dudalen hon yn lle <em>{ $websiteUrl }</em>.
+about-httpsonly-suggestion-box-www-button = Mynd i www.{ $websiteUrl }
diff --git a/thunderbird-l10n/cy/localization/cy/toolkit/about/aboutLogging.ftl b/thunderbird-l10n/cy/localization/cy/toolkit/about/aboutLogging.ftl
new file mode 100644
index 0000000000..bbccf5aa6d
--- /dev/null
+++ b/thunderbird-l10n/cy/localization/cy/toolkit/about/aboutLogging.ftl
@@ -0,0 +1,69 @@
+# This Source Code Form is subject to the terms of the Mozilla Public
+# License, v. 2.0. If a copy of the MPL was not distributed with this
+# file, You can obtain one at http://mozilla.org/MPL/2.0/.
+
+# This is the title of the page
+about-logging-title = Ynghylch Cofnodi
+about-logging-page-title = Logging manager
+about-logging-current-log-file = Ffeil Cofnodi Cyfredol:
+about-logging-new-log-file = Ffeil cofnod newydd:
+about-logging-currently-enabled-log-modules = Modiwlau cofnod wedi'u galluogi ar hyn o bryd:
+about-logging-log-tutorial = Gw <a data-l10n-name="logging">HTTP Logging</a> am wybodaeth ar sut i ddefnyddio'r teclyn hwn.
+# This message is used as a button label, "Open" indicates an action.
+about-logging-open-log-file-dir = Agor y cyfeiriadur
+about-logging-set-log-file = Gosod Ffeil Cofnodi
+about-logging-set-log-modules = Gosod Modiwlau Cofnodi
+about-logging-start-logging = Cychwyn Cofnodi
+about-logging-stop-logging = Peidio Cofnodi
+about-logging-buttons-disabled = Mae'r cofnodi wedi'i ffurfweddu trwy newidynnau amgylcheddol, nid yw ffurfweddu deinamig ar gael.
+about-logging-some-elements-disabled = Mae'r cofnodi wedi'i ffurfweddu trwy URL, nid oes rhai dewisiadau ffurfweddu ar gael
+about-logging-info = Gwybodaeth:
+about-logging-log-modules-selection = Dewisiadau modiwlau cofnodi
+about-logging-new-log-modules = Modiwlau cofnodi newydd:
+about-logging-logging-output-selection = Allbwn cofnodi
+about-logging-logging-to-file = Cofnodi i ffeil
+about-logging-logging-to-profiler = Cofnodi i { -profiler-brand-name }
+about-logging-no-log-modules = Dim
+about-logging-no-log-file = Dim
+about-logging-logging-preset-selector-text = Rhagosodiad cofnodi:
+about-logging-with-profiler-stacks-checkbox = Galluogi olion stac ar gyfer negeseuon cofnodion
+
+## Logging presets
+
+about-logging-preset-networking-label = Rhwydweithio
+about-logging-preset-networking-description = Cofnodi modiwlau er mwyn datrys materion rhwydweithio
+about-logging-preset-networking-cookie-label = Cwcis
+about-logging-preset-networking-cookie-description = Cofnodi modiwlau i wneud diagnosis o broblemau cwci
+about-logging-preset-networking-websocket-label = WebSockets
+about-logging-preset-networking-websocket-description = Cofnodi modiwlau er mwyn datrys materion WebSocket
+about-logging-preset-networking-http3-label = HTTP/3
+about-logging-preset-networking-http3-description = Cofnodi modiwlau er mwyn datrys materion HTTP/3 a QUIC
+about-logging-preset-networking-http3-upload-speed-label = Cyflymder llwytho HTTP/3
+about-logging-preset-networking-http3-upload-speed-description = Modiwlau cofnodi i wneud diagnosis o faterion cyflymder
+about-logging-preset-media-playback-label = Chwarae cyfryngau
+about-logging-preset-media-playback-description = Cofnodi modiwlau i ddatrys materion chwarae cyfryngau (nid materion fideo-gynadledda)
+about-logging-preset-webrtc-label = WebRTC
+about-logging-preset-webrtc-description = Cofnodi modiwlau er mwyn datrys materion galwadau WebRTC
+about-logging-preset-webgpu-label = WebGPU
+about-logging-preset-webgpu-description = Modiwlau cofnodi i wneud diagnosis o faterion WebGPU
+about-logging-preset-gfx-label = Graffigau
+about-logging-preset-gfx-description = Modiwlau cofnodi i wneud diagnosis o broblemau graffigau
+# This is specifically "Microsoft Windows". Microsoft normally doesn't localize it, and we should follow their convention here.
+about-logging-preset-windows-label = Windows
+about-logging-preset-windows-description = Cofnodi modiwlau i wneud diagnosis o faterion sy'n benodol i Microsoft Windows
+about-logging-preset-custom-label = Cyfaddas
+about-logging-preset-custom-description = Modiwlau cofnodion wedi'u dewis â llaw
+# Error handling
+about-logging-error = Gwall:
+
+## Variables:
+##   $k (String) - Variable name
+##   $v (String) - Variable value
+
+about-logging-invalid-output = Gwerth annilys “{ $v }“ ar gyfer allwedd “{ $k }“
+about-logging-unknown-logging-preset = Rhagosodiad cofnodi anhysbys “{ $v }“
+about-logging-unknown-profiler-preset = Rhagosodiad proffiliwr anhysbys “{ $v }“
+about-logging-unknown-option = Dewis about:logging anhysbys “{ $k }“
+about-logging-configuration-url-ignored = Anwybyddwyd URL ffurfweddiad
+about-logging-file-and-profiler-override = Methu â gorfodi allbwn ffeil a diystyru dewisiadau proffiliwr ar yr un pryd
+about-logging-configured-via-url = Dewis wedi'i ffurfweddu trwy URL
diff --git a/thunderbird-l10n/cy/localization/cy/toolkit/about/aboutMozilla.ftl b/thunderbird-l10n/cy/localization/cy/toolkit/about/aboutMozilla.ftl
new file mode 100644
index 0000000000..411039d846
--- /dev/null
+++ b/thunderbird-l10n/cy/localization/cy/toolkit/about/aboutMozilla.ftl
@@ -0,0 +1,11 @@
+# This Source Code Form is subject to the terms of the Mozilla Public
+# License, v. 2.0. If a copy of the MPL was not distributed with this
+# file, You can obtain one at http://mozilla.org/MPL/2.0/.
+
+about-mozilla-title-6-27 = Llyfr Mozilla, 6:27
+about-mozilla-quote-6-27 =
+    The Beast continued its studies with renewed <em>Focus</em>, building great <em>Reference</em>
+    works and contemplating new <em>Realities</em>. The Beast brought forth its followers and
+    acolytes to create a renewed smaller form of itself and, through <em>Mischievous</em> means,
+    sent it out across the world.
+about-mozilla-from-6-27 = o <strong>Lyfr Mozilla,</strong> 6:27
diff --git a/thunderbird-l10n/cy/localization/cy/toolkit/about/aboutNetworking.ftl b/thunderbird-l10n/cy/localization/cy/toolkit/about/aboutNetworking.ftl
new file mode 100644
index 0000000000..55d8054d96
--- /dev/null
+++ b/thunderbird-l10n/cy/localization/cy/toolkit/about/aboutNetworking.ftl
@@ -0,0 +1,68 @@
+# This Source Code Form is subject to the terms of the Mozilla Public
+# License, v. 2.0. If a copy of the MPL was not distributed with this
+# file, You can obtain one at http://mozilla.org/MPL/2.0/.
+
+about-networking-title = Ynghylch Rhwydweithio
+about-networking-http = HTTP
+about-networking-sockets = Socedi
+about-networking-dns = DNS
+about-networking-dns-clear-cache-button = Clirio'r Storfa DNS
+about-networking-dns-trr-url = URL DoH
+about-networking-dns-trr-mode = Modd DoH
+about-networking-dns-suffix = Ôl-ddodiad DNS
+about-networking-websockets = WebSockets
+about-networking-refresh = Adnewyddu
+about-networking-auto-refresh = Adnewyddu pob 3 eiliad
+about-networking-hostname = Enw Gwesteiwr
+about-networking-port = Porth
+about-networking-http-version = Fersiwn HTTP
+about-networking-ssl = SSL
+about-networking-active = Gweithredol
+about-networking-idle = Segur
+about-networking-host = Gwesteiwr
+about-networking-type = Math
+about-networking-sent = Anfonwyd
+about-networking-received = Derbyniwyd
+about-networking-family = Teulu
+about-networking-trr = TRR
+about-networking-addresses = Cyfeiriadau
+about-networking-expires = Daw i ben (Eiliadau)
+about-networking-originAttributesSuffix = Allwedd Ynysu
+about-networking-flags = Baneri ychwanegol
+about-networking-messages-sent = Negeseuon Anfonwyd
+about-networking-messages-received = Negeseuon Derbyniwyd
+about-networking-bytes-sent = Didau Wedi'u Hanfon
+about-networking-bytes-received = Didau Wedi'u Derbyn
+about-networking-logging = Cofnodi
+about-networking-dns-lookup = Chwilio DNS
+about-networking-dns-lookup-button = Datrys
+about-networking-dns-domain = Parth:
+about-networking-dns-lookup-table-column = IPau
+about-networking-dns-https-rr-lookup-table-column = HTTP RRs
+about-networking-rcwn = Statws RCWN
+about-networking-rcwn-status = Statws RCWN
+about-networking-rcwn-cache-won-count = Cyfrif storfa dros dro wedi ei ennill
+about-networking-rcwn-net-won-count = Cyfrif rhwyd wedi ei ennill
+about-networking-total-network-requests = Cyfanswm cyfrif ceisiadau rhwydwaith
+about-networking-rcwn-operation = Gweithred Storfa Dros Dro
+about-networking-rcwn-perf-open = Agor
+about-networking-rcwn-perf-read = Darllen
+about-networking-rcwn-perf-write = Ysgrifennu
+about-networking-rcwn-perf-entry-open = Cofnod Ar Agor
+about-networking-rcwn-avg-short = Cyfartaledd Hir
+about-networking-rcwn-avg-long = Cyfartaledd Hir
+about-networking-rcwn-std-dev-long = Gwyriad Safonol Hir
+about-networking-rcwn-cache-slow = Cyfrif araf storfa dros dro
+about-networking-rcwn-cache-not-slow = Cyfrif nid araf storfa dros dro
+about-networking-networkid = ID Rhwydwaith
+about-networking-networkid-id = ID Rhwydwaith
+# Note: do not translate about:logging, as it is a URL.
+about-networking-moved-about-logging = Mae'r dudalen hon wedi'i symud i <a data-l10n-name="about-logging-url">about:logging</a>.
+
+## Link is intended as "network link"
+
+about-networking-networkid-is-up = Mae'r cyswllt ar i fyny
+about-networking-networkid-status-known = Mae statws y cyswllt yn hysbys
+
+##
+
diff --git a/thunderbird-l10n/cy/localization/cy/toolkit/about/aboutPerformance.ftl b/thunderbird-l10n/cy/localization/cy/toolkit/about/aboutPerformance.ftl
new file mode 100644
index 0000000000..9743697b5d
--- /dev/null
+++ b/thunderbird-l10n/cy/localization/cy/toolkit/about/aboutPerformance.ftl
@@ -0,0 +1,66 @@
+# This Source Code Form is subject to the terms of the Mozilla Public
+# License, v. 2.0. If a copy of the MPL was not distributed with this
+# file, You can obtain one at http://mozilla.org/MPL/2.0/.
+
+# Page title
+about-performance-title = Rheolwr Tasgau
+
+## Column headers
+
+column-name = Enw
+column-type = Math
+column-energy-impact = Effaith Ynni
+column-memory = Cof
+
+## Special values for the Name column
+
+ghost-windows = Tabiau wedi’u cau’n ddiweddar
+# Variables:
+#   $title (String) - the title of the preloaded page, typically 'New Tab'
+preloaded-tab = Rhaglwytho: { $title }
+
+## Values for the Type column
+
+type-tab = Tab
+type-subframe = Is-ffrâm
+type-tracker = Traciwr
+type-addon = Ychwanegyn
+type-browser = Porwr
+type-worker = Gweithiwr
+type-other = Arall
+
+## Values for the Energy Impact column
+##
+## Variables:
+##   $value (Number) - Value of the energy impact, eg. 0.25 (low),
+##                     5.38 (medium), 105.38 (high)
+
+energy-impact-high = Uchel ({ $value })
+energy-impact-medium = Canolig ({ $value })
+energy-impact-low = Isel ({ $value })
+
+## Values for the Memory column
+##
+## Variables:
+##   $value (Number) - How much memory is used
+
+size-KB = { $value } KB
+size-MB = { $value } MB
+size-GB = { $value } GB
+
+## Tooltips for the action buttons
+
+close-tab =
+    .title = Cau tab
+show-addon =
+    .title = Dangos yn y Rheolwr Ychwanegion
+# Tooltip when hovering an item of the about:performance table
+# Variables:
+#   $totalDispatches (Number) - how many dispatches occurred for this page since it loaded
+#   $totalDuration (Number) - how much CPU time was used by this page since it loaded
+#   $dispatchesSincePrevious (Number) - how many dispatches occurred in the last 2 seconds
+#   $durationSincePrevious (Number) - how much CPU time was used in the last 2 seconds
+item =
+    .title =
+        Negeseuon ers llwytho: { $totalDispatches } ({ $totalDuration } ms)
+        Negeseuon yn yr eiliadau diwethaf: { $dispatchesSincePrevious } ({ $durationSincePrevious } ms)
diff --git a/thunderbird-l10n/cy/localization/cy/toolkit/about/aboutPlugins.ftl b/thunderbird-l10n/cy/localization/cy/toolkit/about/aboutPlugins.ftl
new file mode 100644
index 0000000000..5584a6a894
--- /dev/null
+++ b/thunderbird-l10n/cy/localization/cy/toolkit/about/aboutPlugins.ftl
@@ -0,0 +1,43 @@
+# This Source Code Form is subject to the terms of the Mozilla Public
+# License, v. 2.0. If a copy of the MPL was not distributed with this
+# file, You can obtain one at http://mozilla.org/MPL/2.0/.
+
+title-label = Ynghylch Ategion
+installed-plugins-label = Ategion wedi eu gosod
+no-plugins-are-installed-label = Heb ganfod ategion wedi eu gosod
+deprecation-description = Colli rhywbeth? Nid yw rhai ategion yn cael eu cynnal. <a data-l10n-name="deprecation-link">Darllen Rhagor.</a>
+deprecation-description2 =
+    .message = Colli rhywbeth? Nid yw rhai ategion yn cael eu cynnal.
+
+## The information of plugins
+##
+## Variables:
+##   $pluginLibraries: the plugin library
+##   $pluginFullPath: path of the plugin
+##   $version: version of the plugin
+
+file-dd = <span data-l10n-name="file">Ffeil:</span> { $pluginLibraries }
+path-dd = <span data-l10n-name="path">Llwybr:</span> { $pluginFullPath }
+version-dd = <span data-l10n-name="version">Fersiwn:</span> { $version }
+
+## These strings describe the state of plugins
+##
+## Variables:
+##   $blockListState: show some special state of the plugin, such as blocked, outdated
+
+state-dd-enabled = <span data-l10n-name="state">Sir/Talaith:</span> Galluogwyd
+state-dd-enabled-block-list-state = <span data-l10n-name="state">Sir/Talaith:</span> Galluogwyd ({ $blockListState })
+state-dd-Disabled = <span data-l10n-name="state">Sir/Talaith:</span> Analluogwyd
+state-dd-Disabled-block-list-state = <span data-l10n-name="state">Sir/Talaith:</span> Analluogwyd ({ $blockListState })
+mime-type-label = Math MIME
+description-label = Disgrifiad
+suffixes-label = Rhagosodiad
+
+## Gecko Media Plugins (GMPs)
+
+plugins-gmp-license-info = Manylion trwyddedu
+plugins-gmp-privacy-info = Manylion Preifatrwydd
+plugins-openh264-name = OpenH264 Video Codec wedi ei ddarparu gan Cisco Systems, Inc.
+plugins-openh264-description = Mae'r ategyn hwn yn cael ei osod yn awtomatig gan Mozilla er mwyn cyd-fynd â manyleb y WebRTC ac i alluogi galwadau WebRTC gyda dyfeisiau sydd angen y codec fideo H.264. Ewch i http://www.openh264.org/ i weld y cod ffynhonnell a darllen rhagor am ei ddefnyddio.
+plugins-widevine-name = Mae'r Widevine Content Decryption Module wedi ei ddarparu gan Google Inc.
+plugins-widevine-description = Mae'r ategyn hwn yn galluogi chwarae cyfryngau amgryptiedig yn unol â manyleb Estyniadau Cyfryngau Amgryptiedig. Fel rheol defnyddir cyfryngau wedi'i amgryptio gan wefannau i ddiogelu rhag copïo cynnwys cyfryngau premiwm. Ewch i https://www.w3.org/TR/encrypted-media/ am fwy o wybodaeth ar Estyniadau Cyfryngau Amgryptiedig.
diff --git a/thunderbird-l10n/cy/localization/cy/toolkit/about/aboutProcesses.ftl b/thunderbird-l10n/cy/localization/cy/toolkit/about/aboutProcesses.ftl
new file mode 100644
index 0000000000..2434f916a6
--- /dev/null
+++ b/thunderbird-l10n/cy/localization/cy/toolkit/about/aboutProcesses.ftl
@@ -0,0 +1,201 @@
+# This Source Code Form is subject to the terms of the Mozilla Public
+# License, v. 2.0. If a copy of the MPL was not distributed with this
+# file, You can obtain one at http://mozilla.org/MPL/2.0/.
+
+# Page title
+about-processes-title = Rheolwr Prosesau
+# The Actions column
+about-processes-column-action =
+    .title = Gweithredoedd
+
+## Tooltips
+
+about-processes-shutdown-process =
+    .title = Dadlwytho tabiau a lladd y broses
+about-processes-shutdown-tab =
+    .title = Cau tab
+# Profiler icons
+# Variables:
+#    $duration (Number) The time in seconds during which the profiler will be running.
+#                       The value will be an integer, typically less than 10.
+about-processes-profile-process =
+    .title =
+        { $duration ->
+            [zero] Proffilio'r holl edafedd y broses hon am { $duration } eiliad
+            [one] Proffilio'r holl edafedd y broses hon am { $duration } eiliad
+            [two] Proffilio'r holl edafedd y broses hon am { $duration } eiliad
+            [few] Proffilio'r holl edafedd y broses hon am { $duration } eiliad
+            [many] Proffilio'r holl edafedd y broses hon am { $duration } eiliad
+           *[other] Proffilio'r holl edafedd y broses hon am { $duration } eiliad
+        }
+
+## Column headers
+
+about-processes-column-name = Enw
+about-processes-column-memory-resident = Cof
+about-processes-column-cpu-total = CPU
+
+## Process names
+## Variables:
+##    $pid (String) The process id of this process, assigned by the OS.
+
+about-processes-browser-process = { -brand-short-name } ({ $pid })
+about-processes-web-process = Proses We a Rennir ({ $pid })
+about-processes-file-process = Ffeiliau ({ $pid })
+about-processes-extension-process = Estyniadau ({ $pid })
+about-processes-privilegedabout-process = Ynglŷn â thudalennau ({ $pid })
+about-processes-plugin-process = Ategion ({ $pid })
+about-processes-privilegedmozilla-process = Gwefannau { -vendor-short-name } ({ $pid })
+about-processes-gmp-plugin-process = Ategion Cyfryngau Gecko ({ $pid })
+about-processes-gpu-process = GPU ({ $pid })
+about-processes-vr-process = VR ({ $pid })
+about-processes-rdd-process = Datgodiwr Data ({ $pid })
+about-processes-socket-process = Rhwydwaith ({ $pid })
+about-processes-remote-sandbox-broker-process = Brocer Blwch Tywod Pell ({ $pid })
+about-processes-fork-server-process = Gweinydd Fforc ({ $pid })
+about-processes-preallocated-process = Wedi'i rhagddyrannu ({ $pid })
+about-processes-utility-process = Gwasanaeth ({ $pid })
+# Unknown process names
+# Variables:
+#    $pid (String) The process id of this process, assigned by the OS.
+#    $type (String) The raw type for this process.
+about-processes-unknown-process = Arall: { $type } ({ $pid })
+
+## Isolated process names
+## Variables:
+##    $pid (String) The process id of this process, assigned by the OS.
+##    $origin (String) The domain name for this process.
+
+about-processes-web-isolated-process = { $origin } ({ $pid })
+about-processes-web-serviceworker = { $origin } ({ $pid }, gweithiwr gwasanaeth)
+about-processes-with-coop-coep-process = { $origin } ({ $pid }, traws-darddiad ynysig)
+about-processes-web-isolated-process-private = { $origin } — Preifat ({ $pid })
+about-processes-with-coop-coep-process-private = { $origin } — Preifat ({ $pid }, traws-darddiad ynysig)
+
+## Details within processes
+
+# Single-line summary of threads (non-idle process)
+# Variables:
+#    $number (Number) The number of threads in the process. Typically larger
+#                     than 30. We don't expect to ever have processes with less
+#                     than 5 threads.
+#    $active (Number) The number of active threads in the process.
+#                     The value will be greater than 0 and will never be
+#                     greater than $number.
+#    $list (String) Comma separated list of active threads.
+#                   Can be an empty string if the process is idle.
+about-processes-active-threads =
+    { $active ->
+        [zero] { $active } edafedd gweithredol allan o { $number }:{ $list }
+        [one] { $active } edafedd gweithredol allan o { $number }:{ $list }
+        [two] { $active } edafedd gweithredol allan o { $number }:{ $list }
+        [few] { $active } edafedd gweithredol allan o { $number }:{ $list }
+        [many] { $active } edafedd gweithredol allan o { $number }:{ $list }
+       *[other] { $active } edafedd gweithredol allan o { $number }:{ $list }
+    }
+# Single-line summary of threads (idle process)
+# Variables:
+#    $number (Number) The number of threads in the process. Typically larger
+#                     than 30. We don't expect to ever have processes with less
+#                     than 5 threads.
+#                     The process is idle so all threads are inactive.
+about-processes-inactive-threads =
+    { $number ->
+        [zero] { $number } edafedd anweithredol
+        [one] { $number } edafedd anweithredol
+        [two] { $number } edafedd anweithredol
+        [few] { $number } edafedd anweithredol
+        [many] { $number } edafedd anweithredol
+       *[other] { $number } edafedd anweithredol
+    }
+# Thread details
+# Variables:
+#   $name (String) The name assigned to the thread.
+#   $tid (String) The thread id of this thread, assigned by the OS.
+about-processes-thread-name-and-id = { $name }
+    .title = ID edafedd: { $tid }
+# Tab
+# Variables:
+#   $name (String) The name of the tab (typically the title of the page, might be the url while the page is loading).
+about-processes-tab-name = Tab: { $name }
+about-processes-preloaded-tab = Tab Newydd wedi'i Rhag-lwytho
+# Single subframe
+# Variables:
+#   $url (String) The full url of this subframe.
+about-processes-frame-name-one = Is-ffrâm: { $url }
+# Group of subframes
+# Variables:
+#   $number (Number) The number of subframes in this group. Always ≥ 1.
+#   $shortUrl (String) The shared prefix for the subframes in the group.
+about-processes-frame-name-many = Is-fframiau ({ $number }): { $shortUrl }
+
+## Utility process actor names
+
+about-processes-utility-actor-unknown = Actor anhysbys
+about-processes-utility-actor-audio-decoder-generic = Datgodiwr Sain Generig
+about-processes-utility-actor-audio-decoder-applemedia = Datgodiwr Sain Apple Media
+about-processes-utility-actor-audio-decoder-wmf = Datgodiwr Sain Fframwaith Windows Media
+about-processes-utility-actor-mf-media-engine = CDM Media Engine Windows Media Foundation
+# "Oracle" refers to an internal Firefox process and should be kept in English
+about-processes-utility-actor-js-oracle = JavaScript Oracle
+about-processes-utility-actor-windows-utils = Windows Utils
+about-processes-utility-actor-windows-file-dialog = Deialog Ffeil Windows
+
+## Displaying CPU (percentage and total)
+## Variables:
+##    $percent (Number) The percentage of CPU used by the process or thread.
+##                      Always > 0, generally <= 200.
+##    $total (Number) The amount of time used by the process or thread since
+##                    its start.
+##    $unit (String) The unit in which to display $total. See the definitions
+##                   of `duration-unit-*`.
+
+# Common case.
+about-processes-cpu = { NUMBER($percent, maximumSignificantDigits: 2, style: "percent") }
+    .title = Cyfanswm amser CPU: { NUMBER($total, maximumFractionDigits: 0) }{ $unit }
+# Special case: data is not available yet.
+about-processes-cpu-user-and-kernel-not-ready = (yn mesur)
+# Special case: process or thread is almost idle (using less than 0.1% of a CPU core).
+# This case only occurs on Windows where the precision of the CPU times is low.
+about-processes-cpu-almost-idle = <0.1%
+    .title = Cyfanswm amser CPU: { NUMBER($total, maximumFractionDigits: 0) }{ NUMBER($total, maximumFractionDigits: 0) }{ $unit }
+# Special case: process or thread is currently idle.
+about-processes-cpu-fully-idle = yn segur
+    .title = Cyfanswm amser CPU { NUMBER($total, maximumFractionDigits: 0) }{ NUMBER($total, maximumFractionDigits: 0) }{ $unit }
+
+## Displaying Memory (total and delta)
+## Variables:
+##    $total (Number) The amount of memory currently used by the process.
+##    $totalUnit (String) The unit in which to display $total. See the definitions
+##                        of `memory-unit-*`.
+##    $delta (Number) The absolute value of the amount of memory added recently.
+##    $deltaSign (String) Either "+" if the amount of memory has increased
+##                        or "-" if it has decreased.
+##    $deltaUnit (String) The unit in which to display $delta. See the definitions
+##                        of `memory-unit-*`.
+
+# Common case.
+about-processes-total-memory-size-changed = { NUMBER($total, maximumFractionDigits: 0) }{ $totalUnit }
+    .title = Esblygiad: { $deltaSign }{ NUMBER($delta, maximumFractionDigits: 0) }{ $deltaUnit }
+# Special case: no change.
+about-processes-total-memory-size-no-change = { NUMBER($total, maximumFractionDigits: 0) }{ $totalUnit }
+
+## Duration units
+
+duration-unit-ns = ns
+duration-unit-us = µs
+duration-unit-ms = ms
+duration-unit-s = e
+duration-unit-m = m
+duration-unit-h = a
+duration-unit-d = d
+
+## Memory units
+
+memory-unit-B = B
+memory-unit-KB = KB
+memory-unit-MB = MB
+memory-unit-GB = GB
+memory-unit-TB = TB
+memory-unit-PB = PB
+memory-unit-EB = EB
diff --git a/thunderbird-l10n/cy/localization/cy/toolkit/about/aboutProfiles.ftl b/thunderbird-l10n/cy/localization/cy/toolkit/about/aboutProfiles.ftl
new file mode 100644
index 0000000000..6f53902fcf
--- /dev/null
+++ b/thunderbird-l10n/cy/localization/cy/toolkit/about/aboutProfiles.ftl
@@ -0,0 +1,74 @@
+# This Source Code Form is subject to the terms of the Mozilla Public
+# License, v. 2.0. If a copy of the MPL was not distributed with this
+# file, You can obtain one at http://mozilla.org/MPL/2.0/.
+
+
+profiles-title = Ynghylch Proffiliau
+profiles-subtitle = Mae'r dudalen hon yn eich helpu i reoli eich proffiliau. Mae pob proffil yn fyd ar wahân sy'n cynnwys hanes, nodau tudalen, gosodiadau ac yn ychwanegion gwahanol.
+profiles-create = Creu Proffil Newydd
+profiles-restart-title = Ailgychwyn
+profiles-restart-in-safe-mode = Ailgychwyn gydag Ychwanegion wedi eu Hanablu…
+profiles-restart-normal = Ailgychwyn fel arfer…
+profiles-conflict = Mae copi arall o { -brand-product-name } wedi gwneud newidiadau i broffiliau. Rhaid ailgychwyn { -brand-short-name } cyn gwneud mwy o newidiadau.
+profiles-flush-fail-title = Heb gadw'r newidiadau
+profiles-flush-conflict = { profiles-conflict }
+profiles-flush-failed = Mae gwall annisgwyl wedi atal eich newidiadau rhag cael eu cadw.
+profiles-flush-restart-button = Ailgychwyn { -brand-short-name }
+
+# Variables:
+#   $name (String) - Name of the profile
+profiles-name = Proffil: { $name }
+profiles-is-default = Proffil Ragosodedig
+profiles-rootdir = Cyfarwyddiadur Gwraidd
+
+# localDir is used to show the directory corresponding to
+# the main profile directory that exists for the purpose of storing data on the
+# local filesystem, including cache files or other data files that may not
+# represent critical user data. (e.g., this directory may not be included as
+# part of a backup scheme.)
+# In case localDir and rootDir are equal, localDir is not shown.
+profiles-localdir = Cyfarwyddiadur Lleol
+profiles-current-profile = Dyma'r proffil sy'n cael ei ddefnyddio ac nid oes modd ei ddileu.
+profiles-in-use-profile = Mae'r proffil yn cael ei ddefnyddio o fewn rhaglen arall ac nid oes modd ei ddileu.
+
+profiles-rename = Ailenwi
+profiles-remove = Tynnu
+profiles-set-as-default = Gosod fel y proffil ragosodedig
+profiles-launch-profile = Cychwyn proffil yn y porwr newydd
+
+profiles-cannot-set-as-default-title = Methu gosod y rhagosodedig
+profiles-cannot-set-as-default-message = Nid oes modd newid y proffil rhagosodedig am { -brand-short-name }.
+
+profiles-yes = iawn
+profiles-no = na
+
+profiles-rename-profile-title = Newid Enw Proffil
+# Variables:
+#   $name (String) - Name of the profile
+profiles-rename-profile = Ailenwi proffil { $name }
+
+profiles-invalid-profile-name-title = Enw proffil annilys
+# Variables:
+#   $name (String) - Name of the profile
+profiles-invalid-profile-name = Methu caniatáu enw proffil "{ $name }".
+
+profiles-delete-profile-title = Dileu Proffil
+# Variables:
+#   $dir (String) - Path to be displayed
+profiles-delete-profile-confirm =
+    Bydd dileu proffil yn tynnu'r proffil o'r rhestr o broffiliau sydd ar gael ac nid oes modd ei ddadwneud.
+    Gallwch hefyd ddewis i ddileu ffeiliau data proffil, gan gynnwys eich gosodiadau, tystysgrifau a data arall yn perthyn i ddefnyddwyr. Bydd y dewis hwn yn dileu ffolder "{ $dir }" ac nid oes modd ei ddadwneud.
+    Hoffech chi ddileu'r ffeiliau data proffil?
+profiles-delete-files = Dileu Ffeiliau
+profiles-dont-delete-files = Peidio Dileu Ffeiliau
+
+profiles-delete-profile-failed-title = Gwall
+profiles-delete-profile-failed-message = Bu gwall wrth geisio dileu'r proffil hwn.
+
+
+profiles-opendir =
+    { PLATFORM() ->
+        [macos] Dangos yn Finder
+        [windows] Agor Ffolder
+       *[other] Agor Cyfeiriadur
+    }
diff --git a/thunderbird-l10n/cy/localization/cy/toolkit/about/aboutReader.ftl b/thunderbird-l10n/cy/localization/cy/toolkit/about/aboutReader.ftl
new file mode 100644
index 0000000000..400440656a
--- /dev/null
+++ b/thunderbird-l10n/cy/localization/cy/toolkit/about/aboutReader.ftl
@@ -0,0 +1,56 @@
+# This Source Code Form is subject to the terms of the Mozilla Public
+# License, v. 2.0. If a copy of the MPL was not distributed with this
+# file, You can obtain one at http://mozilla.org/MPL/2.0/.
+
+about-reader-loading = Yn llwytho…
+about-reader-load-error = Methwyd llwytho erthygl o dudalen
+
+about-reader-color-scheme-light = Golau
+    .title = Cynllun Lliw Golau
+about-reader-color-scheme-dark = Tywyll
+    .title = Cynllun Lliw Tywyll
+about-reader-color-scheme-sepia = Sepia
+    .title = Cynllun Lliw Sepia
+about-reader-color-scheme-auto = Awtomatig
+    .title = Cynllun Lliw Awtomatig
+
+# An estimate for how long it takes to read an article,
+# expressed as a range covering both slow and fast readers.
+# Variables:
+#   $rangePlural (String): The plural category of the range, using the same set as for numbers.
+#   $range (String): The range of minutes as a localised string. Examples: "3-7", "~1".
+about-reader-estimated-read-time =
+    { $rangePlural ->
+        [zero] Dim munudau
+        [one] { $range } munud
+        [two] { $range } munud
+        [few] { $range } munud
+        [many] { $range } munud
+       *[other] { $range } munud
+    }
+
+## These are used as tooltips in Type Control
+
+about-reader-toolbar-minus =
+    .title = Lleihau Maint Testun
+about-reader-toolbar-plus =
+    .title = Cynyddu Maint Testun
+about-reader-toolbar-contentwidthminus =
+    .title = Lleihau Lled Cynnwys
+about-reader-toolbar-contentwidthplus =
+    .title = Cynyddu Lled Cynnwys
+about-reader-toolbar-lineheightminus =
+    .title = Lleihau Uchder Llinell
+about-reader-toolbar-lineheightplus =
+    .title = Cynyddu Uchder Llinell
+
+## These are the styles of typeface that are options in the reader view controls.
+
+about-reader-font-type-serif = Serif
+about-reader-font-type-sans-serif = Sans-serif
+
+## Reader View toolbar buttons
+
+about-reader-toolbar-close = Cau'r Golwg Darllen
+about-reader-toolbar-type-controls = Rheoli'r math
+about-reader-toolbar-savetopocket = Cadw i { -pocket-brand-name }
diff --git a/thunderbird-l10n/cy/localization/cy/toolkit/about/aboutRights.ftl b/thunderbird-l10n/cy/localization/cy/toolkit/about/aboutRights.ftl
new file mode 100644
index 0000000000..541a34c7f7
--- /dev/null
+++ b/thunderbird-l10n/cy/localization/cy/toolkit/about/aboutRights.ftl
@@ -0,0 +1,36 @@
+# This Source Code Form is subject to the terms of the Mozilla Public
+# License, v. 2.0. If a copy of the MPL was not distributed with this
+# file, You can obtain one at http://mozilla.org/MPL/2.0/.
+
+rights-title = Ynghylch eich hawliau
+rights-intro = Mae { -brand-full-name } yn feddalwedd cod agored rhydd a rhad, wedi ei adeiladu gan gymuned o filoedd o bobl ar draws y byd i gyd. Mae yna rhai pethau i chi gael gwybod:
+rights-intro-point-1 = Mae { -brand-short-name } ar gael i chi o dan amodau'r <a data-l10n-name="mozilla-public-license-link">Trwydded Gyhoeddus Mozilla</a>. Mae hyn yn golygu y cewch ddefnyddio, gopïo a dosbarthu { -brand-short-name } i eraill.  Mae croeso i chi newid cod ffynhonnell { -brand-short-name } yn ôl eich angen. Mae Trwydded Gyhoeddus Mozilla yn rhoi'r hawl i chi ddosbarthu'r fersiwn rydych wedi ei newid.
+rights-intro-point-2 = Nid ydych yn derbyn unrhyw hawliau nod masnachu na thrwyddedau i nod masnach y Mozilla Foundation neu unrhyw barti, gan gynnwys y Mozzilla Foundation heb gyfyngiadau i enw na logo Firefox. Mae gwybodaeth bellach am nodau masnach i’w cael <a data-l10n-name="mozilla-trademarks-link">yma</a>.
+rights-intro-point-3 = Mae rhai nodweddion yn { -brand-short-name }, megis yr Adroddwr Chwalu, yn rhoi'r dewis i chi gyfrannu adborth i { -vendor-short-name }. Drwy ddewis cyflwyno adborth rydych yn rhoi i { -vendor-short-name } ganiatâd i ddefnyddio'r adborth i wella ei gynnyrch, i gyhoeddi'r adborth ar ei wefannau, ac i ddosbarthu'r adborth.
+rights-intro-point-4 = Mae sut rydym yn defnyddio y data personol ac adborth rydych wedi ei gyflwyno i { -vendor-short-name } drwy { -brand-short-name } yn cael ei ddisgrifio yn <a data-l10n-name="mozilla-privacy-policy-link">Polisi Preifatrwydd { -brand-short-name }</a>.
+rights-intro-point-4-unbranded = Rhaid rhestri unrhyw bolisïau preifatrwydd perthnasol yma.
+rights-intro-point-5 = Mae rhai nodweddion { -brand-short-name } yn gwneud defnydd p wasanaethau gwybodaeth gwe, er hynny nid ydym yn gallu gwarantu eu bod yn 100% yn gywir nac yn rhydd o wallau. Mae rhagor o fanylion, gan gynnwys gwybodaeth ar sut i'w hanalluogi i'w cael yn yr <a data-l10n-name="mozilla-service-terms-link">amodau gwasanaeth</a>.
+rights-intro-point-5-unbranded = Os yw'r cynnyrch yn cynnwys gwasanaethau gwe, rhaid cysylltu unrhyw amodau gwasanaeth perthnasol ar gyfer y gwasanaeth(au) i'r adran <a data-l10n-name="mozilla-website-services-link">Gwasanaethau Gwefan</a> Gwe.
+rights-intro-point-6 = Er mwyn chwarae rhai mathau o gynnwys fideo, mae { -brand-short-name } yn llwytho i lawr rhywfaint o gynnwys modiwlau dadgryptio gan drydydd partïon.
+rights-webservices-header = Gwasanaethau Gwybodaeth Gwe { -brand-full-name }
+rights-webservices = Mae { -brand-full-name } yn defnyddio gwasanaethau gwybodaeth gwe ("Gwasanaethau") i ddarparu rhai o'r nodweddion sy'n cael eu darparu ar eich cyfer yn y fersiwn yma o { -brand-short-name } o fewn yr amodau disgrifir isod. Os nad ydych am ddefnyddio un neu fwy o'r Gwasanaethau neu mae'r amodau yn annerbyniol, mae modd i chi analluogi'r nodwedd neu'r Gwasanaeth(au). Mae gwybodaeth ar sut i analluogi nodwedd neu Wasanaeth penodol i'w cael <a data-l10n-name="mozilla-disable-service-link">yma</a>. Mae modd analluogi nodweddion a Gwasanaethau eraill yn newisiadau'r rhaglen.
+rights-safebrowsing = <strong>Pori Diogel: </strong>Nid yw anablu Pori Diogel yn cael ei gymeradwyo gan y gall arwain i chi fynd i wefannau anniogel.  Os ydych eisiau analluogi'r nodwedd yn llwyr, dilynwch y camau hyn:
+rights-safebrowsing-term-1 = Agor dewisiadau'r rhaglen
+rights-safebrowsing-term-2 = Dewis Diogelwch
+rights-safebrowsing-term-3 = Dad dicio'r dewis i "{ enableSafeBrowsing-label }"
+enableSafeBrowsing-label = Rhwystro cynnwys peryglus a thwyllodrus
+rights-safebrowsing-term-4 = Mae Pori Diogel wedi ei analluogi
+rights-locationawarebrowsing = <strong>Pori Ymwybodol o Leoliad: </strong>yn ddewis i chi bob tro.  Ni fydd gwybodaeth yn cael ei anfon heb eich caniatâd.  Os hoffech chi analluogi'r nodwedd yn llwyr, dilynwch y camau hyn:
+rights-locationawarebrowsing-term-1 = Yn y bar URL, teipiwch <code>about:config</code>
+rights-locationawarebrowsing-term-2 = Teipio geo.enabled
+rights-locationawarebrowsing-term-3 = Clic dwbl i'r dewis geo.enabled
+rights-locationawarebrowsing-term-4 = Mae Pori Ymwybodol o Leoliad wedi ei analluogi
+rights-webservices-unbranded = Rhaid cynnwys yn fan hyn, drosolwg o'r gwasanaeth gwefan gwe mae'r cynnyrch yn ei gynnwys, ynghyd â chyfarwyddiadau ar sut i'w hatal os yn berthnasol.
+rights-webservices-term-unbranded = Rhaid rhestru amodau gwasanaethau gwe yma.
+rights-webservices-term-1 = Mae { -vendor-short-name } a'i gyfranwyr, trwyddedwyr, a phartneriaid yn gweithio i ddarparu'r Gwasanaethau mwyaf cywir a chyfredol.  Er hynny, nid oes modd i ni warantu fod y wybodaeth yn gynhwysfawr a diwall.  Er enghraifft, efallai na fydd y Gwasanaeth Pori Diogel yn adnabod rhai gwefannau anniogel ac efallai adnabod rhai gwefannau diogel ar gam. Mae pob lleoliad sy'n cael ei ddychwelyd gan ein darparwyr gwasanaeth ar gyfer y Gwasanaeth Ymwybodol o Leoliad yn amcanion yn unig. Nid ydym ni na'r darparwyr gwasanaeth yn gallu gwarantu cywirdeb y lleoliadau hyn.
+rights-webservices-term-2 = Gall { -vendor-short-name } atal neu newid y Gwasanaethau yn ôl eu mympwy.
+rights-webservices-term-3 = Mae croeso i chi ddefnyddio'r Gwasanaethau hyn gyda'r fersiwn yma o { -brand-short-name }, ac mae { -vendor-short-name } rhoi ei hawl i chi wneud hynny.  Mae { -vendor-short-name } a'i drwyddedwyr yn diogelu pob hawl arall yn y Gwasanaethau.  Nid yw'r amodau wedi eu hanelu at gyfyngu unrhyw hawliau o dan drwyddedau cod agored sy'n perthyn i { -brand-short-name } ac i'r fersiynau perthnasol o ffynonellau cod { -brand-short-name }.
+rights-webservices-term-4 = <strong>Mae'r gwasanaeth yn cael ei ddarparu "fel ag y mae".  Mae { -vendor-short-name }, ei gyfranwyr, trwyddedwyr, a dosbarthwyr, yn gwadu unrhyw warant, p'un ai yn cael ei fynegi neu ei awgrymu, gan gynnwys heb gyfyngiad, gwarant fod y Gwasanaethau yn farchnadadwy nac yn addas i'ch pwrpas penodol.  Rydych yn derbyn yr holl risg o ddewis y Gwasanaethau ar gyfer eich pwrpas ac i natur ansawdd a pherfformiad y Gwasanaeth. Nid yw rhai awdurdodau'n caniatáu eithrio neu gyfyngu gwarant sy'n cael ei awgrymu felly efallai nad yw'r gwadiad hwn yn berthnasol i chi.</strong>
+rights-webservices-term-5 = <strong>Yn wahanol i'r hyn sy'n angenrheidiol yn ôl y gyfraith, ni fydd { -vendor-short-name }, ei gyfranwyr, trwyddedwyr a dosbarthwyr yn agored i unrhyw iawndal anuniongyrchol, arbenigol, achlysurol, neu enghreifftiol yn codi o neu mewn unrhyw ffordd yn berthnasol i'r defnydd o { -brand-short-name } a'r Gwasanaethau.   Ni fydd yr atebolrwydd cyfunol o dan yr amodau hyn yn fwy na $500 (pum can dollar). Nid yw rhai awdurdodau yn caniatáu cyfyngu ar rhai materion difrod, felly efallai na fydd hyn yn berthnasol i chi.</strong>
+rights-webservices-term-6 = Gall { -vendor-short-name } ddiweddaru'r amodau yn ôl y galw o bryd i'w gilydd. Nid oes modd newid na dileu'r amodau heb ganiatâd ysgrifenedig { -vendor-short-name }.
+rights-webservices-term-7 = Mae'r amodau yn cael eu rheoli gan gyfreithiau talaith California, UDA, gan hepgor ei ddarpariaethau gwrthdaro cyfreithiol. Os yw unrhyw ran o'r amodau i'w cael heb rym cyfreithiol byd y gweddill yn sefyll mewn grym llawn ac effaith. Os digwydd gwrthdaro rhwng fersiwn sydd wedi ei gyfieithu a'r amodau hyn a'r fersiwn Saesneg, y fersiwn Saesneg fydd yn rheoli.
diff --git a/thunderbird-l10n/cy/localization/cy/toolkit/about/aboutServiceWorkers.ftl b/thunderbird-l10n/cy/localization/cy/toolkit/about/aboutServiceWorkers.ftl
new file mode 100644
index 0000000000..9474662afb
--- /dev/null
+++ b/thunderbird-l10n/cy/localization/cy/toolkit/about/aboutServiceWorkers.ftl
@@ -0,0 +1,40 @@
+# This Source Code Form is subject to the terms of the Mozilla Public
+# License, v. 2.0. If a copy of the MPL was not distributed with this
+# file, You can obtain one at http://mozilla.org/MPL/2.0/.
+
+
+### The term "Service Workers" and "Workers" should not be translated
+
+about-service-workers-title = Ynghylch Service Workers
+about-service-workers-main-title = Service Workers Cofrestredig
+about-service-workers-warning-not-enabled = Nid yw Service Workers wedi eu galluogi.
+about-service-workers-warning-no-service-workers = Does dim Service Workers wedi eu cofrestru.
+
+# The original title of service workers' information
+#
+# Variables:
+#   $originTitle: original title
+origin-title = Tarddiad: { $originTitle }
+
+## These strings are for showing the information of workers.
+##
+## Variables:
+##  $name: the name of scope, active cache, waiting cache and the push end point.
+##  $url: the url of script specification and current worker.
+
+scope = <strong>Ystod:</strong> { $name }
+script-spec = <strong>Manyleb Sgript:</strong> <a data-l10n-name="link">{ $url }</a>
+current-worker-url = <strong>URL Worker Cyfredol:</strong> <a data-l10n-name="link">{ $url }</a>
+active-cache-name = <strong>Enw'r Storfa Dros Dro Weithredol:</strong> { $name }
+waiting-cache-name = <strong>Enw'r Storfa Dros Dro sy'n Aros:</strong> { $name }
+push-end-point-waiting = <strong>Push Endpoint:</strong> { waiting }
+push-end-point-result = <strong>Push Endpoint:</strong> { $name }
+
+# This term is used as a button label (verb, not noun).
+update-button = Diweddaru
+
+unregister-button = Dadgofrestru
+
+unregister-error = Methwyd dadgofrestru'r Service Workers.
+
+waiting = Aros…
diff --git a/thunderbird-l10n/cy/localization/cy/toolkit/about/aboutSupport.ftl b/thunderbird-l10n/cy/localization/cy/toolkit/about/aboutSupport.ftl
new file mode 100644
index 0000000000..537d0d4114
--- /dev/null
+++ b/thunderbird-l10n/cy/localization/cy/toolkit/about/aboutSupport.ftl
@@ -0,0 +1,446 @@
+# This Source Code Form is subject to the terms of the Mozilla Public
+# License, v. 2.0. If a copy of the MPL was not distributed with this
+# file, You can obtain one at http://mozilla.org/MPL/2.0/.
+
+page-title = Gwybodaeth am Ddatrys Problemau
+page-subtitle = Mae'r dudalen hon yn cynnwys gwybodaeth dechnegol a allai fod yn ddefnyddiol pan fyddwch yn ceisio datrys problem. Os ydych yn chwilio am atebion i gwestiynau cyffredin am { -brand-short-name }, edrychwch ar ein <a data-l10n-name="support-link">gwefan cefnogaeth</a>.
+crashes-title = Adroddiadau Chwalu
+crashes-id = Enw'r Adroddiad
+crashes-send-date = Cyflwynwyd
+crashes-all-reports = Pob Adroddiad Chwalu
+crashes-no-config = Mae'r rhaglen wedi ei ffurfweddu i ddangos adroddiadau chwalu.
+support-addons-title = Ychwanegion
+support-addons-name = Enw
+support-addons-type = Math
+support-addons-enabled = Galluogwyd
+support-addons-version = Fersiwn
+support-addons-id = ID
+legacy-user-stylesheets-title = Hen Ddalenni Arddull Defnyddiwr
+legacy-user-stylesheets-enabled = Gweithredol
+legacy-user-stylesheets-stylesheet-types = Dalenni arddull
+legacy-user-stylesheets-no-stylesheets-found = Heb ganfod dalenni arddull
+security-software-title = Meddalwedd Diogelwch
+security-software-type = Math
+security-software-name = Enw
+security-software-antivirus = Gwrth Firws
+security-software-antispyware = Gwrthysbiwar
+security-software-firewall = Mur Cadarn
+features-title = Nodweddion { -brand-short-name }
+features-name = Enw
+features-version = Fersiwn
+features-id = ID
+processes-title = Prosesau Pell
+processes-type = Math
+processes-count = Cyfrif
+app-basics-title = Sylfaeni'r Rhaglen
+app-basics-name = Enw
+app-basics-version = Fersiwn
+app-basics-build-id = Cyfeirnod Adeiladu
+app-basics-distribution-id = ID Dosbarthu
+app-basics-update-channel = Sianel Diweddaru
+# This message refers to the folder used to store updates on the device,
+# as in "Folder for updates". "Update" is a noun, not a verb.
+app-basics-update-dir =
+    { PLATFORM() ->
+        [linux] Diweddaru Cyfeiriadur
+       *[other] Diweddaru Ffolder
+    }
+app-basics-update-history = Hanes Diweddaru
+app-basics-show-update-history = Dangos Hanes Diweddaru
+# Represents the path to the binary used to start the application.
+app-basics-binary = Deuaidd y Rhaglen
+app-basics-profile-dir =
+    { PLATFORM() ->
+        [linux] Cyfeiriadur Proffil
+       *[other] Ffolder Proffil
+    }
+app-basics-enabled-plugins = Ategion Galluogwyd
+app-basics-build-config = Ffurfweddiad Adeiladu
+app-basics-user-agent = Asiant Defnyddiwr
+app-basics-os = SW
+app-basics-os-theme = Thema OS
+# Rosetta is Apple's translation process to run apps containing x86_64
+# instructions on Apple Silicon. This should remain in English.
+app-basics-rosetta = Cyfieithu gan Rosetta
+app-basics-memory-use = Defnydd o'r cof
+app-basics-performance = Perfformiad
+app-basics-service-workers = Service Workers Cofrestredig
+app-basics-third-party = Modiwlau Trydydd Parti
+app-basics-profiles = Proffiliau
+app-basics-launcher-process-status = Proses Lansio
+app-basics-multi-process-support = Ffenestri Amlbroses
+app-basics-fission-support = Ffenestri Fission
+app-basics-remote-processes-count = Prosesau Pell
+app-basics-enterprise-policies = Polisïau Mentrau
+app-basics-location-service-key-google = Allwedd Google Location Service
+app-basics-safebrowsing-key-google = Allwedd Google Safebrowsing
+app-basics-key-mozilla = Mozilla Location Service Key
+app-basics-safe-mode = Modd Diogel
+app-basics-memory-size = Maint Cof (RAM)
+app-basics-disk-available = Lle ar Ddisg ar Gael
+app-basics-pointing-devices = Dyfeisiau Pwyntio
+# Variables:
+#   $value (number) - Amount of data being stored
+#   $unit (string) - The unit of data being stored (e.g. MB)
+app-basics-data-size = { $value } { $unit }
+show-dir-label =
+    { PLATFORM() ->
+        [macos] Dangos yn Finder
+        [windows] Agor Ffolder
+       *[other] Agor Cyfeiriadur
+    }
+environment-variables-title = Newidiolion Amgylcheddol
+environment-variables-name = Enw
+environment-variables-value = Gwerth
+experimental-features-title = Nodweddion Arbrofol
+experimental-features-name = Enw
+experimental-features-value = Gwerth
+modified-key-prefs-title = Dewisiadau Pwysig wedi eu Newid
+modified-prefs-name = Enw
+modified-prefs-value = Gwerth
+user-js-title = Dewisiadau user.js
+user-js-description = Mae eich ffolder profil yn cynnwys <a data-l10n-name="user-js-link">ffeil user.js</a>, sy'n cynnwys dewisiadau sydd heb eu creu gan { -brand-short-name }.
+locked-key-prefs-title = Dewisiadau Pwysig Wedi eu Cloi
+locked-prefs-name = Enw
+locked-prefs-value = Gwerth
+graphics-title = Graffigau
+graphics-features-title = Nodweddion
+graphics-diagnostics-title = Diagnosteg
+graphics-failure-log-title = Cofnod Methiant
+graphics-gpu1-title = GPU #1
+graphics-gpu2-title = GPU #2
+graphics-decision-log-title = Cofnod Penderfynnu
+graphics-crash-guards-title = Nodweddion Crash Guard wedi ei Analluogi
+graphics-workarounds-title = Dulliau Datrys
+graphics-device-pixel-ratios = Cymarebau Picsel Dyfais Ffenestr
+# Windowing system in use on Linux (e.g. X11, Wayland).
+graphics-window-protocol = Protocol Ffenestr
+# Desktop environment in use on Linux (e.g. GNOME, KDE, XFCE, etc).
+graphics-desktop-environment = Amgylchedd Bwrdd Gwaith
+place-database-title = Cronfa Ddata Mannau
+place-database-stats = Ystadegau
+place-database-stats-show = Dangos Ystadegau
+place-database-stats-hide = Cuddio Ystadegau
+place-database-stats-entity = Endid
+place-database-stats-count = Cyfrif
+place-database-stats-size-kib = Maint (KiB)
+place-database-stats-size-perc = Maint (%)
+place-database-stats-efficiency-perc = Effeithlonrwydd (%)
+place-database-stats-sequentiality-perc = Dilynianedd (%)
+place-database-integrity = Cyfanrwydd
+place-database-verify-integrity = Gwirio Cyfanrwydd
+a11y-title = Hygyrchedd
+a11y-activated = Gweithredu
+a11y-force-disabled = Atal Hygyrchedd
+a11y-handler-used = Defnyddiwyd Trinydd Mynediadwy
+a11y-instantiator = Enghreifftiad Hygyrchedd
+library-version-title = Fersiynau Llyfrgell
+copy-text-to-clipboard-label = Copïo testun i'r clipfwrdd
+copy-raw-data-to-clipboard-label = Copïo data bras i'r clipfwrdd
+sandbox-title = Blwch tywod
+sandbox-sys-call-log-title = Galwadau System wedi eu Gwrthod
+sandbox-sys-call-index = #
+sandbox-sys-call-age = Eiliad yn Ôl
+sandbox-sys-call-pid = PID
+sandbox-sys-call-tid = TID
+sandbox-sys-call-proc-type = Math o Brosesu
+sandbox-sys-call-number = Syscall
+sandbox-sys-call-args = Ymresymiadau
+troubleshoot-mode-title = Datrys materion
+restart-in-troubleshoot-mode-label = Y Modd Datrys Problemau…
+clear-startup-cache-title = Ceisiwch glirio'r storfa gychwyn
+clear-startup-cache-label = Clirio'r storfa gychwyn…
+startup-cache-dialog-title2 = Ailgychwyn { -brand-short-name } i glirio'r storfa cychwyn?
+startup-cache-dialog-body2 = Ni fydd hyn yn newid eich gosodiadau nac yn dileu estyniadau.
+restart-button-label = Ailgychwyn
+
+## Media titles
+
+audio-backend = Cefn Sain
+max-audio-channels = Mwyaf o Sianeli
+sample-rate = Graddfa Samplo Amgen
+roundtrip-latency = Cylchdro cudd (gwyriad safonol)
+media-title = Cyfrwng
+media-output-devices-title = Dyfeisiau Allbwn
+media-input-devices-title = Dyfeisiau Mewnbwn
+media-device-name = Enw
+media-device-group = Grŵp
+media-device-vendor = Gwerthwr
+media-device-state = Cyflwr
+media-device-preferred = Amgen
+media-device-format = Fformat
+media-device-channels = Sianeli
+media-device-rate = Cyfradd
+media-device-latency = Cuddni
+media-capabilities-title = Gallu Cyfryngol
+media-codec-support-info = Gwybodaeth Gymorth Codec
+# List all the entries of the database.
+media-capabilities-enumerate = Cyfrifo'r gronfa ddata
+
+## Codec support table
+
+media-codec-support-sw-decoding = Datgodio Meddalwedd
+media-codec-support-hw-decoding = Datgodio Caledwedd
+media-codec-support-codec-name = Enw Codec
+media-codec-support-supported = Cefnogaeth
+media-codec-support-unsupported = Heb eu Cynnal
+media-codec-support-error = Nid yw manylion cymorth codec ar gael. Ceisiwch eto ar ôl chwarae ffeil cyfryngau.
+media-codec-support-lack-of-extension = Gosod estyniad
+
+## Media Content Decryption Modules (CDM)
+## See EME Spec for more explanation for following technical terms
+## https://w3c.github.io/encrypted-media/
+
+media-content-decryption-modules-title = Manylion Modiwlau Dadgryptio Cynnwys
+media-key-system-name = Enw System Allwedd
+media-video-robustness = Cadernid Fideo
+media-audio-robustness = Cadernid Sain
+media-cdm-capabilities = Galluoedd
+# Clear Lead isn't defined in the spec, which means the the first few seconds
+# are not encrypted. It allows playback to start without having to wait for
+# license response, improving video start time and user experience.
+media-cdm-clear-lead = Cychwyn Clir (Clear Lead)
+
+##
+
+intl-title = Rhyngwladoli a Lleoleiddio
+intl-app-title = Gosodiadau'r Rhaglen
+intl-locales-requested = Locales Gofynnwyd Amdanynt
+intl-locales-available = Locales ar Gael
+intl-locales-supported = Locales Apiau
+intl-locales-default = Locale Rhagosodedig
+intl-os-title = System Weithredu
+intl-os-prefs-system-locales = Locales y System
+intl-regional-prefs = Dewisiadau Rhanbarthol
+
+## Remote Debugging
+##
+## The Firefox remote protocol provides low-level debugging interfaces
+## used to inspect state and control execution of documents,
+## browser instrumentation, user interaction simulation,
+## and for subscribing to browser-internal events.
+##
+## See also https://firefox-source-docs.mozilla.org/remote/
+
+remote-debugging-title = Dadfygio o Bell (Protocol Cromiwm)
+remote-debugging-accepting-connections = Derbyn Cysylltiadau
+remote-debugging-url = URL
+
+##
+
+# Variables
+# $days (Integer) - Number of days of crashes to log
+report-crash-for-days =
+    { $days ->
+        [zero] Ni fu Adroddiadau Chwalu
+        [one] Adroddiadau Chwalu'r { $days } Diwrnod Diwethaf
+        [two] Adroddiadau Chwalu'r { $days } Ddiwrnod Diwethaf
+        [few] Adroddiadau Chwalu'r { $days } Diwrnod Diwethaf
+        [many] Adroddiadau chwalu'r { $days } Diwrnod Diwethaf
+       *[other] Adroddiadau chwalu'r { $days } Diwrnod Diwethaf
+    }
+# Variables
+# $minutes (integer) - Number of minutes since crash
+crashes-time-minutes =
+    { $minutes ->
+        [zero] Dim munudau yn ôl
+        [one] { $minutes } munud yn ôl
+        [two] { $minutes } funud yn ôl
+        [few] { $minutes } munud yn ôl
+        [many] { $minutes } munud yn ôl
+       *[other] { $minutes } munud yn ôl
+    }
+# Variables
+# $hours (integer) - Number of hours since crash
+crashes-time-hours =
+    { $hours ->
+        [zero] Dim oriau yn ôl
+        [one] { $hours } awr yn ôl
+        [two] { $hours } awr yn ôl
+        [few] { $hours } awr yn ôl
+        [many] { $hours } awr yn ôl
+       *[other] { $hours } awr yn ôl
+    }
+# Variables
+# $days (integer) - Number of days since crash
+crashes-time-days =
+    { $days ->
+        [zero] Dim dyddiau yn ôl
+        [one] { $days } diwrnod yn ôl
+        [two] { $days } ddiwrnod yn ôl
+        [few] { $days } diwrnod yn ôl
+        [many] { $days } diwrnod yn ôl
+       *[other] { $days } diwrnod yn ôl
+    }
+# Variables
+# $reports (integer) - Number of pending reports
+pending-reports =
+    { $reports ->
+        [zero] Dim Adroddiadau Chwalu
+        [one] Pob Adroddiad Chwalu (gan gynnwys { $reports } chwalfa disgwyliedig o fewn ystod penodol o amser)
+        [two] Pob Adroddiad Chwalu (gan gynnwys { $reports } chwalfa disgwyliedig o fewn ystod penodol o amser)
+        [few] Pob Adroddiad Chwalu (gan gynnwys { $reports } chwalfa disgwyliedig o fewn ystod penodol o amser)
+        [many] Pob Adroddiad Chwalu (gan gynnwys { $reports } chwalfa disgwyliedig o fewn ystod penodol o amser)
+       *[other] Pob Adroddiad Chwalu (gan gynnwys { $reports } chwalfa disgwyliedig o fewn ystod penodol o amser)
+    }
+raw-data-copied = Copïwyd data bras i'r clipfwrdd
+text-copied = Copïwyd testun i'r clipfwrdd
+
+## The verb "blocked" here refers to a graphics feature such as "Direct2D" or "OpenGL layers".
+
+blocked-driver = Wedi ei rwystro ar gyfer y fersiwn o'ch gyrrwr graffigol chi.
+blocked-gfx-card = Wedi ei rwystro ar gyfer eich cerdyn graffigol oherwydd pryderon gyrrwr heb eu datrys.
+blocked-os-version = Wedi ei rwystro ar gyfer eich fersiwn chi o'r system weithredu.
+blocked-mismatched-version = Rhwystro ar gyfer gwrthdaro fersiwn gyrrwr graffig y gofrestrfa a'r DLL.
+# Variables
+# $driverVersion - The graphics driver version string
+try-newer-driver = Wedi ei rwystro ar gyfer eich gyrrwr graffigol chi. Ceisiwch ddiweddaru'r gyrrwr i fersiwn { $driverVersion } neu ddiweddarach.
+# "ClearType" is a proper noun and should not be translated. Feel free to leave English strings if
+# there are no good translations, these are only used in about:support
+clear-type-parameters = Paramedrau ClearType
+compositing = Cyfosod
+hardware-h264 = Dadgodio Caledwedd H264
+main-thread-no-omtc = prif drywydd, dim OMTC
+yes = Iawn
+no = Na
+unknown = Anhysbys
+virtual-monitor-disp = Dangosiad Monitor Rhithwir
+
+## The following strings indicate if an API key has been found.
+## In some development versions, it's expected for some API keys that they are
+## not found.
+
+found = Wedi Canfod
+missing = Coll
+gpu-process-pid = GPUProcessPid
+gpu-process = GPUProcess
+gpu-description = Disgrifiad
+gpu-vendor-id = Enw'r Gwerthwr
+gpu-device-id = Enw Dyfais
+gpu-subsys-id = Enw subsys
+gpu-drivers = Gyrwyr
+gpu-ram = RAM
+gpu-driver-vendor = Gwerthwr Gyrwyr
+gpu-driver-version = Fersiwn Gyrrwr
+gpu-driver-date = Dyddiad y Gyrrwr
+gpu-active = Gweithredol
+webgl1-wsiinfo = Gwybodaeth WSI ar yrrwr WebGL 1
+webgl1-renderer = Rendrwr Gyrrwr WebGL 1
+webgl1-version = Fersiwn Gyrrwr WebGL 1
+webgl1-driver-extensions = Estyniadau Gyrrwr WebGL 1
+webgl1-extensions = Estyniadau WebGL 1
+webgl2-wsiinfo = Gwybodaeth WSI Gyrrwr WebGL 2
+webgl2-renderer = Rendrwr Gyrrwr WebGL 2
+webgl2-version = Fersiwn Gyrrwr WebGL 2
+webgl2-driver-extensions = Estyniadau Gyrrwr WebGL 2
+webgl2-extensions = Estyniadau WebGL 2
+webgpu-default-adapter = Addasydd Rhagosodedig WebGPU
+webgpu-fallback-adapter = Addasydd wrth Gefn WebGPU
+# Variables
+#   $bugNumber (string) - Bug number on Bugzilla
+support-blocklisted-bug = Ar y Rhestr Rhwystro oherwydd materion hysbys: <a data-l10n-name="bug-link">bug { $bugNumber }</a>
+# Variables
+# $failureCode (string) - String that can be searched in the source tree.
+unknown-failure = Wedi ei rwystro; gwall cod { $failureCode }
+d3d11layers-crash-guard = Cyfosodwr D3D11
+glcontext-crash-guard = OpenGL
+wmfvpxvideo-crash-guard = Dadgodiwr Fideo WMF VPX
+reset-on-next-restart = Ailosod wrth Ailgychwyn
+gpu-process-kill-button = Gorffen Proses GPU
+gpu-device-reset = Ailosod Dyfais
+gpu-device-reset-button = Ailosod Dyfais Trigro
+uses-tiling = Yn defnyddio Teilsio
+content-uses-tiling = Yn Defnyddio Teilsio (Cynnwys)
+off-main-thread-paint-enabled = Galluogwyd Paentio All Brif Drywydd
+off-main-thread-paint-worker-count = Cyfrif Gweithiwr Paentio Oddi ar y Brif Drywydd
+target-frame-rate = Graddfa Ffrâm Darged
+min-lib-versions = Fersiwn lleiaf disgwyliedig
+loaded-lib-versions = Fersiwn mewn defnydd
+has-seccomp-bpf = Seccomp-BPF (Hidlo Galw System)
+has-seccomp-tsync = Cydweddiad Edafedd Seccomp
+has-user-namespaces = Bylchau Enwau Defnyddiwr
+has-privileged-user-namespaces = Bylchau Enw Defnyddiwr fel prosesau breintiedig
+can-sandbox-content = Blwch Tywod Proses Cynnwys
+can-sandbox-media = Blwch Tywod Ategyn Cyfrwng
+content-sandbox-level = Lefel Blwch Tywod Proses Cynnwys
+effective-content-sandbox-level = Lefel Blwch Tywod Proses Cynnwys Effeithiol
+content-win32k-lockdown-state = Cyflwr Clo Win32k ar gyfer y Broses Cynnwys
+support-sandbox-gpu-level = Lefel Blwch Tywod Proses GPU
+sandbox-proc-type-content = cynnwys
+sandbox-proc-type-file = cynnwys ffeil
+sandbox-proc-type-media-plugin = ategyn cyfrwng
+sandbox-proc-type-data-decoder = datgodydd data
+startup-cache-title = Storfa cychwyn
+startup-cache-disk-cache-path = Llwybr Storfa Disg
+startup-cache-ignore-disk-cache = Anwybyddu Storfa Disg
+startup-cache-found-disk-cache-on-init = Wedi dod o hyd i Storfa Disg ar Init
+startup-cache-wrote-to-disk-cache = Ysgrifennwyd at Storfa Disg
+launcher-process-status-0 = Galluogwyd
+launcher-process-status-1 = Analluogwyd oherwydd methiant
+launcher-process-status-2 = Analluogwyd yn orfodol
+launcher-process-status-unknown = Statws anhysbys
+# Variables
+# $remoteWindows (integer) - Number of remote windows
+# $totalWindows (integer) - Number of total windows
+multi-process-windows = { $remoteWindows }/{ $totalWindows }
+# Variables
+# $fissionWindows (integer) - Number of remote windows
+# $totalWindows (integer) - Number of total windows
+fission-windows = { $fissionWindows }/{ $totalWindows }
+fission-status-experiment-control = Analluogwyd trwy arbrawf
+fission-status-experiment-treatment = Galluogwyd trwy arbrawf
+fission-status-disabled-by-e10s-env = Analluogwyd gan yr amgylchedd
+fission-status-enabled-by-env = Galluogwyd gan yr amgylchedd
+fission-status-disabled-by-env = Analluogwyd gan yr amgylchedd
+fission-status-enabled-by-default = Galluogwyd drwy ragosodiad
+fission-status-disabled-by-default = Analluogwyd drwy ragosodiad
+fission-status-enabled-by-user-pref = Galluogwyd gan y defnyddiwr
+fission-status-disabled-by-user-pref = Analluogwyd gan y defnyddiwr
+fission-status-disabled-by-e10s-other = E10s wedi ei analluogi
+fission-status-enabled-by-rollout = Wedi'i alluogi trwy ei gyflwyno fesul cam
+async-pan-zoom = Chwyddo a Thremio Anghydamseredig
+apz-none = dim
+wheel-enabled = mewnbwn olwyn wedi ei alluogi
+touch-enabled = mewnbwn cyffwrdd wedi ei alluogi
+drag-enabled = wedi galluogu llusgo bar sgrolio
+keyboard-enabled = bysellfwrdd wedi ei anlluogi
+autoscroll-enabled = galluogwyd awtosgrolio
+zooming-enabled = pinsio chwyddo llyfn wedi'i alluogi
+
+## Variables
+## $preferenceKey (string) - String ID of preference
+
+wheel-warning = Mae mewnbwn olwyn async wedi ei analluogi oherwydd diffyg cefnogaeth pref: { $preferenceKey }
+touch-warning = Mae mewnbwn cyffwrdd async wedi ei analluogi oherwydd diffyg cefnogaeth pref: { $preferenceKey }
+
+## Strings representing the status of the Enterprise Policies engine.
+
+policies-inactive = Anweithredol
+policies-active = Gweithredol
+policies-error = Gwall
+
+## Printing section
+
+support-printing-title = Yn argraffu
+support-printing-troubleshoot = Datrys Anawsterau
+support-printing-clear-settings-button = Clirio gosodiadau argraffu wedi'u cadw
+support-printing-modified-settings = Gosodiadau argraffu wedi'u haddasu
+support-printing-prefs-name = Enw
+support-printing-prefs-value = Gwerth
+
+## Normandy sections
+
+support-remote-experiments-title = Arbrofion Pell
+support-remote-experiments-name = Enw
+support-remote-experiments-branch = Cangen Arbrofi
+support-remote-experiments-see-about-studies = Gweler <a data-l10n-name="support-about-studies-link">about:studies</a> i gael mwy o wybodaeth, gan gynnwys sut i analluogi arbrofion unigol neu i analluogi { -brand-short-name } rhag rhedeg y math yma o arbrawf yn y dyfodol.
+support-remote-features-title = Nodweddion Pell
+support-remote-features-name = Enw
+support-remote-features-status = Statws
+
+## Pointing devices
+
+pointing-device-mouse = Llygoden
+pointing-device-touchscreen = Sgrin Cyffwrdd
+pointing-device-pen-digitizer = Digidydd Pen
+pointing-device-none = Dim dyfeisiau pwyntio
diff --git a/thunderbird-l10n/cy/localization/cy/toolkit/about/aboutTelemetry.ftl b/thunderbird-l10n/cy/localization/cy/toolkit/about/aboutTelemetry.ftl
new file mode 100644
index 0000000000..6a529c3261
--- /dev/null
+++ b/thunderbird-l10n/cy/localization/cy/toolkit/about/aboutTelemetry.ftl
@@ -0,0 +1,140 @@
+# This Source Code Form is subject to the terms of the Mozilla Public
+# License, v. 2.0. If a copy of the MPL was not distributed with this
+# file, You can obtain one at http://mozilla.org/MPL/2.0/.
+
+about-telemetry-ping-data-source = Ffynhonnell data ping:
+about-telemetry-show-current-data = Data cyfredol
+about-telemetry-show-archived-ping-data = Data ping wedi ei archifo
+about-telemetry-show-subsession-data = Dangos data is-sesiwn
+about-telemetry-choose-ping = Dewis ping:
+about-telemetry-archive-ping-type = Math Ping
+about-telemetry-archive-ping-header = Ping
+about-telemetry-option-group-today = Heddiw
+about-telemetry-option-group-yesterday = Ddoe
+about-telemetry-option-group-older = Hŷn
+about-telemetry-previous-ping = <<
+about-telemetry-next-ping = >>
+about-telemetry-page-title = Data Telemetreg
+about-telemetry-current-store = Storfa Gyfredol:
+about-telemetry-more-information = Chwilio am ragor o wybodaeth?
+about-telemetry-firefox-data-doc = Mae'r <a data-l10n-name="data-doc-link">Firefox Data Documentation</a> yn cynnwys canllawiau ar sut i weithio gyda'n offer data.
+about-telemetry-telemetry-client-doc = Mae <a data-l10n-name="client-doc-link">dogfennaeth cleient Firefox Telemetry</a> yn cynnwys diffiniadau o gysyniadau, dogfennaeth API a chyfeiriadau data.
+about-telemetry-telemetry-dashboard = Mae <a data-l10n-name="dashboard-link">byrddau gwaith Telemetreg</a> yn caniatáu i chi weld y data mae Mozilla yn ei dderbyn drwy'r Delemetreg.
+about-telemetry-telemetry-probe-dictionary = Mae'r <a data-l10n-name="probe-dictionary-link">Geiriadur Archwilio</a> yn darparu manylion a disgrifiadau ar gyfer y chwilio gasglwyd gan Delemetreg.
+about-telemetry-show-in-Firefox-json-viewer = Agor yn y darllenydd JSON
+about-telemetry-home-section = Cartref
+about-telemetry-general-data-section = Data Cyffredinol
+about-telemetry-environment-data-section = Data'r Amgylchedd
+about-telemetry-session-info-section = Manylion Sesiwn
+about-telemetry-scalar-section = Scalarau
+about-telemetry-keyed-scalar-section = Graddfeydd Allweddedig
+about-telemetry-histograms-section = Histogramau
+about-telemetry-keyed-histogram-section = Histogramau Allweddol
+about-telemetry-events-section = Digwyddiadau
+about-telemetry-simple-measurements-section = Mesuriadau Syml
+about-telemetry-slow-sql-section = Datganiadau SQL Araf
+about-telemetry-addon-details-section = Manylion Ychwanegyn
+about-telemetry-late-writes-section = Ysgrifennu Hwyr
+about-telemetry-raw-payload-section = Llwyth Bras
+about-telemetry-raw = JSON bras
+about-telemetry-full-sql-warning = SYLW: Mae dadfygio SQL araf wedi ei alluogi. Gall llinynnau SQL llawn gael eu dangos isod ond ni fyddant yn cael eu trosglwyddo i'r Telemetreg.
+about-telemetry-fetch-stack-symbols = Estyn enwau swyddogaethau ar gyfer pentyrrau
+about-telemetry-hide-stack-symbols = Dangos data pentwr bras
+# Selects the correct release version
+# Variables:
+#   $channel (string) - Represents the corresponding release data string
+about-telemetry-data-type =
+    { $channel ->
+        [release] ryddhau data
+       *[prerelease] data cyn ryddhau
+    }
+# Selects the correct upload string
+# Variables:
+#   $uploadcase (string) - Represents a corresponding upload string
+about-telemetry-upload-type =
+    { $uploadcase ->
+        [enabled] galluogwyd
+       *[disabled] analluogwyd
+    }
+# Example Output: 1 sample, average = 0, sum = 0
+# Variables:
+#   $sampleCount (number) - Amount of histogram samples
+#   $prettyAverage (number) - Average of histogram samples
+#   $sum (number) - Sum of histogram samples
+about-telemetry-histogram-stats =
+    { $sampleCount ->
+        [zero] { $sampleCount } sampl, cyfartaledd= { $prettyAverage }, swm = { $sum }
+        [one] { $sampleCount } sampl, cyfartaledd= { $prettyAverage }, swm = { $sum }
+        [two] { $sampleCount } sampl, cyfartaledd= { $prettyAverage }, swm = { $sum }
+        [few] { $sampleCount } sampl, cyfartaledd= { $prettyAverage }, swm = { $sum }
+        [many] { $sampleCount } sampl, cyfartaledd= { $prettyAverage }, swm = { $sum }
+       *[other] { $sampleCount } sampl, cyfartaledd= { $prettyAverage }, swm = { $sum }
+    }
+# Variables:
+#   $telemetryServerOwner (string) - the value of the toolkit.telemetry.server_owner preference. Typically "Mozilla"
+about-telemetry-page-subtitle = Mae'r dudalen hon yn dangos gwybodaeth am berfformiad, caledwedd, defnydd a chyfaddasiadau a gasglwyd gan y Delemetreg. Mae'r wybodaeth yn cael ei gyflwyno i { $telemetryServerOwner } er mwyn gwella { -brand-full-name }.
+about-telemetry-settings-explanation = Mae telemetreg yn casglu { about-telemetry-data-type } a'r llwyth yw <a data-l10n-name="upload-link">{ about-telemetry-upload-type }</a>.
+# Variables:
+#   $name (string) - Ping name, e.g. “saved-session”
+#   $timestamp (string) - Ping localized timestamp, e.g. “2017/07/08 10:40:46”
+about-telemetry-ping-details = Mae pob darn o wybodaeth wedi ei anfon wedi ei becynnu i “<a data-l10n-name="ping-link">pingiau</a>”. Rydych yn edrych ar ping { $name }, { $timestamp }.
+about-telemetry-data-details-current = Mae pob darn o wybodaeth yn cael ei anfon wedi'i fwndelu i “<a data-l10n-name="ping-link">bingiadau</a>“. Rydych yn edrych ar y data cyfredol.
+# string used as a placeholder for the search field
+# More info about it can be found here:
+# https://firefox-source-docs.mozilla.org/toolkit/components/telemetry/telemetry/data/main-ping.html
+# Variables:
+#   $selectedTitle (string) - The section name from the structure of the ping.
+about-telemetry-filter-placeholder =
+    .placeholder = Canfod yn y { $selectedTitle }
+about-telemetry-filter-all-placeholder =
+    .placeholder = Canfod ym mhob adran
+# Variables:
+#   $searchTerms (string) - The searched terms
+about-telemetry-results-for-search = Canlyniadau “{ $searchTerms }”
+# More info about it can be found here: https://firefox-source-docs.mozilla.org/toolkit/components/telemetry/telemetry/data/main-ping.html
+# Variables:
+#   $sectionName (string) - The section name from the structure of the ping.
+#   $currentSearchText (string) - The current text in the search input
+about-telemetry-no-search-results = Ymddiheuriadau! Does dim canlyniadau yn { $sectionName } ar gyfer “{ $currentSearchText }”
+# Variables:
+#   $searchTerms (string) - The searched terms
+about-telemetry-no-search-results-all = Ymddiheuriadau! Nid oes canlyniadau i unrhyw adran am “{ $searchTerms }”
+# This message is displayed when a section is empty.
+# Variables:
+#   $sectionName (string) - Is replaced by the section name.
+about-telemetry-no-data-to-display = Ymddiheuriadau! Nid oes data ar gael ar hyn o bryd yn “{ $sectionName }”
+# used as a tooltip for the “current” ping title in the sidebar
+about-telemetry-current-data-sidebar = data cyfredol
+# used in the “Ping Type” select
+about-telemetry-telemetry-ping-type-all = y cyfan
+# button label to copy the histogram
+about-telemetry-histogram-copy = Copïo
+# these strings are used in the “Slow SQL Statements” section
+about-telemetry-slow-sql-main = Datganiadau SQL Araf ar y Prif Drywydd
+about-telemetry-slow-sql-other = Datganiadau SQL Araf ar y Trywyddion Cynorthwyol
+about-telemetry-slow-sql-hits = Trawiadau
+about-telemetry-slow-sql-average = Amser Cyfartalog (ms)
+about-telemetry-slow-sql-statement = Datganiad
+# these strings are used in the “Add-on Details” section
+about-telemetry-addon-table-id = Enw'r Ychwanegyn
+about-telemetry-addon-table-details = Manylion
+# Variables:
+#   $addonProvider (string) - The name of an Add-on Provider (e.g. “XPI”, “Plugin”)
+about-telemetry-addon-provider = Darparwr { $addonProvider }
+about-telemetry-keys-header = Priodwedd
+about-telemetry-names-header = Enw
+about-telemetry-values-header = Gwerth
+# Variables:
+#   $lateWriteCount (number) - The number of the late writes
+about-telemetry-late-writes-title = Ysgrifennu Hwyr #{ $lateWriteCount }
+about-telemetry-stack-title = Stac:
+about-telemetry-memory-map-title = Map cof:
+about-telemetry-error-fetching-symbols = Digwyddodd gwall wrth estyn symbolau. Gwiriwch eich bod wedi eich cysylltu â'r rhyngrwyd a cheisio eto.
+about-telemetry-time-stamp-header = stamp amser
+about-telemetry-category-header = categori
+about-telemetry-method-header = dull
+about-telemetry-object-header = gwrthrych
+about-telemetry-extra-header = ychwanegol
+# Variables:
+#  $process (string) - Type of process in subsection headers ( e.g. "content", "parent" )
+about-telemetry-process = Proses { $process }
diff --git a/thunderbird-l10n/cy/localization/cy/toolkit/about/aboutThirdParty.ftl b/thunderbird-l10n/cy/localization/cy/toolkit/about/aboutThirdParty.ftl
new file mode 100644
index 0000000000..cb36ff8dd8
--- /dev/null
+++ b/thunderbird-l10n/cy/localization/cy/toolkit/about/aboutThirdParty.ftl
@@ -0,0 +1,85 @@
+# This Source Code Form is subject to the terms of the Mozilla Public
+# License, v. 2.0. If a copy of the MPL was not distributed with this
+# file, You can obtain one at http://mozilla.org/MPL/2.0/.
+
+third-party-page-title = Gwybodaeth am Fodiwlau Trydydd Parti
+third-party-section-title = Rhestr o fodiwlau trydydd parti yn { -brand-short-name }
+third-party-intro =
+    Mae'r dudalen hon yn dangos y modiwlau trydydd parti a chwistrellwyd i'ch { -brand-short-name }.
+    Mae unrhyw fodiwl sydd heb ei lofnodi gan Microsoft neu { -vendor-short-name } 
+    yn cael ei ystyried yn fodiwl trydydd parti.
+third-party-message-empty = Heb ganfod unrhyw fodiwlau trydydd parti.
+third-party-message-no-duration = Heb ei recordio
+third-party-detail-version = Fersiwn ffeil
+third-party-detail-vendor = Manylion y gwerthwr
+third-party-detail-occurrences = Amlder
+    .title = Sawl gwaith mae'r modiwl hwn wedi'i lwytho
+third-party-detail-duration = Cyfartaledd amser Rhwystro (ms)
+    .title = Am faint o amser rhwystrodd y modiwl y rhaglen.
+third-party-detail-app = Rhaglen
+third-party-detail-publisher = Cyhoeddwr
+third-party-th-process = Proses
+third-party-th-duration = Cyfnod Llwytho (ms)
+third-party-th-status = Statws
+third-party-tag-ime = IME
+    .title = Mae'r math yma o fodiwl wedi ei lwytho pan fyddwch yn defnyddio IME trydydd parti.
+third-party-tag-shellex = Estyniad Cragen
+    .title = Mae'r math yma o fodiwl wedi ei lwytho pan fyddwch yn agor deialog ffeil y system.
+third-party-tag-background = Cefndir
+    .title =
+        Nid yw'r modiwl yn rhwystro'r rhaglen am ei fod wedi
+        ei lwytho yn y cefndir.
+third-party-icon-unsigned =
+    .title = Nid yw'r modiwl hwn wedi'i lofnodi
+    .alt = Nid yw'r modiwl hwn wedi'i lofnodi
+third-party-icon-warning =
+    .title = Chwalodd { -brand-short-name } yn y cod o'r modiwl hwn
+    .alt = Chwalodd { -brand-short-name } yn y cod o'r modiwl hwn
+third-party-status-loaded = Wedi llwytho
+third-party-status-blocked = Rhwystrwyd
+third-party-status-redirected = Wedi'i ailgyfeirio
+third-party-button-copy-to-clipboard = Copïo data bras i'r clipfwrdd
+third-party-loading-data =
+    .alt = Yn llwytho gwybodaeth system…
+    .title = Yn llwytho gwybodaeth system…
+third-party-button-reload = Ail-lwytho gyda manylion y system
+    .title = Ail-lwytho gyda manylion y system
+third-party-button-open =
+    .title = Agor lleoliad ffeil…
+third-party-button-to-block =
+    .title = Rhwystro'r modiwl hwn
+    .aria-label = Rhwystro'r modiwl hwn
+third-party-button-to-unblock =
+    .title = Wedi'i rwystro ar hyn o bryd. Cliciwch i'w ddadrwystro.
+    .aria-label = Wedi'i rwystro ar hyn o bryd. Cliciwch i'w ddadrwystro.
+third-party-button-to-unblock-disabled =
+    .title =
+        Wedi'i nodi fel wedi'i rwystro ar hyn o bryd, er bod y rhestr rhwystro wedi'i hanalluogi ar gyfer y rhediad hwn
+        o { -brand-short-name }. Cliciwch i'w ddadrwystro.
+    .aria-label =
+        Wedi'i nodi fel wedi'i rwystro ar hyn o bryd, er bod y rhestr rhwystro wedi'i hanalluogi ar gyfer y rhediad hwn
+        o { -brand-short-name }. Cliciwch i'w ddadrwystro.
+third-party-button-to-block-module = Rhwystro'r modiwl hwn
+    .title = Rhwystro'r modiwl hwn
+    .aria-label = Rhwystro'r modiwl hwn
+third-party-button-to-unblock-module = Dadrwystro'r modiwl hwn
+    .title = Wedi'i rwystro. Cliciwch i'w ddadrwystro.
+    .aria-label = Wedi'i rwystro. Cliciwch i'w ddadrwystro.
+third-party-button-to-unblock-module-disabled = Dadrwystro'r modiwl hwn (rhestr rhwystro wedi'i analluogi)
+    .title =
+        Wedi'i nodi fel wedi'i rwystro, er fod y rhestr rhwystro wedi ei analluogi ar gyfer y rhediad yma
+        o { -brand-short-name }. Cliciwch i'w ddadrwystro.
+    .aria-label =
+        Wedi'i nodi fel wedi'i rwystro, er fod y rhestr rhwystro wedi ei analluogi ar gyfer y rhediad yma
+        o { -brand-short-name }. Cliciwch i'w ddadrwystro.
+third-party-button-expand =
+    .title = Dangos gwybodaeth fanwl
+third-party-button-collapse =
+    .title = Cau gwybodaeth fanwl
+third-party-blocking-requires-restart = I rwystro modiwl trydydd parti, rhaid i { -brand-short-name } ailgychwyn.
+third-party-should-restart-title = Ailgychwyn { -brand-short-name }
+third-party-restart-now = Ailgychwyn nawr
+third-party-restart-later = Ailgychwyn yn ddiweddarach
+third-party-blocked-by-builtin =
+    .title = Wedi'i rwystro gan { -brand-short-name }
+    .alt = Wedi'i rwystro gan { -brand-short-name }
diff --git a/thunderbird-l10n/cy/localization/cy/toolkit/about/aboutWebauthn.ftl b/thunderbird-l10n/cy/localization/cy/toolkit/about/aboutWebauthn.ftl
new file mode 100644
index 0000000000..1b94b63275
--- /dev/null
+++ b/thunderbird-l10n/cy/localization/cy/toolkit/about/aboutWebauthn.ftl
@@ -0,0 +1,134 @@
+# This Source Code Form is subject to the terms of the Mozilla Public
+# License, v. 2.0. If a copy of the MPL was not distributed with this
+# file, You can obtain one at http://mozilla.org/MPL/2.0/.
+
+
+### Localization for about:webauthn, a security token management page
+
+# Page title
+# 'WebAuthn' is a protocol name and should not be translated
+about-webauthn-page-title = Ynghylch WebAuthn
+
+## Section titles
+
+about-webauthn-info-section-title = Manylion dyfais
+about-webauthn-info-subsection-title = Manylion dilysydd
+about-webauthn-options-subsection-title = Dewisiadau dilysydd
+about-webauthn-pin-section-title = Rheoli PIN
+about-webauthn-credential-management-section-title = Rheoli manylion
+about-webauthn-pin-required-section-title = Mae angen PIN
+about-webauthn-confirm-deletion-section-title = Cadarnhau dileu
+
+## Info field texts
+
+about-webauthn-text-connect-device = Cysylltwch docyn diogelwch.
+# If multiple devices are plugged in, they will blink and we are asking the user to select one by touching the device they want.
+about-webauthn-text-select-device = Dewiswch eich tocyn diogelwch o'ch dewis trwy gyffwrdd â'r ddyfais.
+# CTAP2 refers to Client to Authenticator Protocol version 2
+about-webauthn-text-non-ctap2-device = Methu â rheoli'r dewisiadau oherwydd nad yw eich tocyn diogelwch yn cefnogi CTAP2.
+about-webauthn-text-not-available = Nid yw ar gael ar y platfform hwn.
+
+## Results label
+
+about-webauthn-results-success = Llwyddiant!
+about-webauthn-results-general-error = Gwall!
+# Variables:
+#  $retriesLeft (Number): number of tries left
+about-webauthn-results-pin-invalid-error =
+    { $retriesLeft ->
+        [0] Gwall: PIN anghywir. Ceisiwch eto.
+        [zero] Gwall: PIN anghywir. Ceisiwch eto. Nid oes gennych unrhyw geisiadau ar ôl.
+        [one] Gwall: PIN anghywir. Ceisiwch eto. Mae gennych un cais ar ôl.
+        [two] Gwall: PIN anghywir. Ceisiwch eto. Mae gennych { $retriesLeft } gais ar ôl.
+        [few] Gwall: PIN anghywir. Ceisiwch eto. Mae gennych { $retriesLeft } chais ar ôl.
+        [many] Gwall: PIN anghywir. Ceisiwch eto. Mae gennych { $retriesLeft } chais ar ôl.
+       *[other] Gwall: PIN anghywir. Ceisiwch eto. Mae gennych { $retriesLeft } cais ar ôl.
+    }
+about-webauthn-results-pin-blocked-error = Gwall: Nid oes unrhyw geisiadau ar ôl ac mae'ch dyfais wedi'i chloi, oherwydd cyflwynwyd y PIN anghywir gormod o weithiau. Mae angen ailosod y ddyfais.
+about-webauthn-results-pin-too-short-error = Gwall: Mae'r PIN hwn yn rhy fyr.
+about-webauthn-results-pin-too-long-error = Gwall: Mae'r PIN hwn yn rhy hir.
+about-webauthn-results-pin-auth-blocked-error = Gwall: Bu gormod o geisiadau wedi methu yn olynol ac mae dilysu PIN wedi'i rwystro dros dro. Mae angen cylchred pŵer ar eich dyfais (dad-blygio ac ail-blygio).
+about-webauthn-results-cancelled-by-user-error = Gwall: Mae'r gweithrediad wedi'i ddiddymu gan y defnyddiwr.
+
+## Labels
+
+about-webauthn-new-pin-label = PIN newydd:
+about-webauthn-repeat-pin-label = Ailadrodd PIN newydd:
+about-webauthn-current-pin-label = Y PIN cyfredol:
+about-webauthn-pin-required-label = Rhowch eich PIN:
+about-webauthn-credential-list-subsection-title = Manylion:
+about-webauthn-credential-list-empty = Dim manylion adnabod ar y ddyfais.
+about-webauthn-confirm-deletion-label = Rydych ar fin dileu:
+
+## Buttons
+
+about-webauthn-current-set-pin-button = Gosod PIN
+about-webauthn-current-change-pin-button = Newid PIN
+# List is a verb, as in "Show list of credentials"
+about-webauthn-list-credentials-button = Rhestru'r manylion personol
+about-webauthn-cancel-button = Diddymu
+about-webauthn-send-pin-button = Iawn
+about-webauthn-delete-button = Dileu
+
+## Authenticator options fields
+## Option fields correspond to the CTAP2 option IDs and definitions found in https://fidoalliance.org/specs/fido-v2.1-ps-20210615/fido-client-to-authenticator-protocol-v2.1-ps-20210615.html#option-id
+
+about-webauthn-auth-option-uv = Dilysiad defnyddiwr
+about-webauthn-auth-option-up = Presenoldeb defnyddiwr
+about-webauthn-auth-option-clientpin = PIN cleient
+about-webauthn-auth-option-rk = Allwedd preswylydd
+about-webauthn-auth-option-plat = Dyfais platfform
+# pinUvAuthToken should not be translated.
+about-webauthn-auth-option-pinuvauthtoken = Caniatâd gorchymyn (pinUvAuthToken)
+# MakeCredential and GetAssertion should not be translated.
+about-webauthn-auth-option-nomcgapermissionswithclientpin = Dim caniatâd MakeCredential / GetAssertion gyda'r PIN cleient
+about-webauthn-auth-option-largeblobs = Blobs mawr
+about-webauthn-auth-option-ep = Ardystiad menter
+about-webauthn-auth-option-bioenroll = Cofrestriad biometrig
+# FIDO_2_1_PRE should not be translated.
+about-webauthn-auth-option-userverificationmgmtpreview = Prototeip o gofrestriad biometrig (FIDO_2_1_PRE)
+about-webauthn-auth-option-uvbioenroll = Caniatâd cofrestriad biometrig
+about-webauthn-auth-option-authnrcfg = Ffurfweddiad y dilysydd
+about-webauthn-auth-option-uvacfg = Caniatâd ffurfweddiad y dilysydd
+about-webauthn-auth-option-credmgmt = Rheoli manylion personol
+about-webauthn-auth-option-credentialmgmtpreview = Rheoli manylion personol prototeip
+about-webauthn-auth-option-setminpinlength = Gosod isafswm hyd PIN
+# MakeCredential should not be translated.
+about-webauthn-auth-option-makecreduvnotrqd = MakeCredential heb ddilysiad defnyddiwr
+about-webauthn-auth-option-alwaysuv = Angen gwirio defnyddiwr bob tro
+# Shows when boolean value for an option is True. True should not be translated.
+about-webauthn-auth-option-true = True
+# Shows when boolean value of an option is False. False should not be translated.
+about-webauthn-auth-option-false = False
+# If the value is missing (null), it means a certain feature is not supported.
+about-webauthn-auth-option-null = Heb ei gefnogi
+
+## Authenticator info fields
+## Info fields correspond to the CTAP2 authenticatorGetInfo field member name and definitions found in https://fidoalliance.org/specs/fido-v2.1-ps-20210615/fido-client-to-authenticator-protocol-v2.1-ps-20210615.html#authenticatorGetInfo
+
+about-webauthn-auth-info-vendor-prototype-config-commands = Gorchmynion ffurfweddu prototeip y gwerthwr
+about-webauthn-auth-info-remaining-discoverable-credentials = Manylion personol darganfyddadwy sy'n weddill
+about-webauthn-auth-info-certifications = Ardystiadau
+about-webauthn-auth-info-uv-modality = Moddion dilysu defnyddwyr
+about-webauthn-auth-info-preferred-platform-uv-attempts = Ymdrechion dilysu dewis platfform y defnyddiwr
+about-webauthn-auth-info-max-rpids-for-set-min-pin-length = IDau partïon mwyaf ar gyfer isafswm hyd PIN penodol
+about-webauthn-auth-info-max-cred-blob-length = Uchafswm hyd blob manylion personol
+about-webauthn-auth-info-firmware-version = Fersiwn cadarnwedd
+about-webauthn-auth-info-min-pin-length = Hyd lleiaf PIN
+about-webauthn-auth-info-force-pin-change = Gorfodi newid PIN
+about-webauthn-auth-info-max-ser-large-blob-array = Maint mwyaf arae blob mawr
+about-webauthn-auth-info-algorithms = Algorithmau
+about-webauthn-auth-info-transports = Cludiant
+about-webauthn-auth-info-max-credential-id-length = Uchafswm hyd ID manylion personol
+about-webauthn-auth-info-max-credential-count-in-list = Uchafswm y cyfrif manylion personol yn y rhestr
+about-webauthn-auth-info-pin-protocols = Protocolau PINiau
+about-webauthn-auth-info-max-msg-size = Uchafswm maint y neges
+# AAGUID should not be translated.
+about-webauthn-auth-info-aaguid = AAGUID
+about-webauthn-auth-info-extensions = Estyniadau
+about-webauthn-auth-info-versions = Fersiynau
+# Shows when boolean value for an info field is True. True should not be translated.
+about-webauthn-auth-info-true = True
+# Shows when boolean value for an info field is False. False should not be translated.
+about-webauthn-auth-info-false = False
+about-webauthn-auth-info-null = Heb ei gefnogi
diff --git a/thunderbird-l10n/cy/localization/cy/toolkit/about/aboutWebrtc.ftl b/thunderbird-l10n/cy/localization/cy/toolkit/about/aboutWebrtc.ftl
new file mode 100644
index 0000000000..24d40a8959
--- /dev/null
+++ b/thunderbird-l10n/cy/localization/cy/toolkit/about/aboutWebrtc.ftl
@@ -0,0 +1,347 @@
+# This Source Code Form is subject to the terms of the Mozilla Public
+# License, v. 2.0. If a copy of the MPL was not distributed with this
+# file, You can obtain one at http://mozilla.org/MPL/2.0/.
+
+
+### Localization for about:webrtc, a troubleshooting and diagnostic page
+### for WebRTC calls. See https://developer.mozilla.org/en-US/docs/Web/API/WebRTC_API.
+
+# The text "WebRTC" is a proper noun and should not be translated.
+about-webrtc-document-title = Materion Mewnol WebRTC
+# "about:webrtc" is a internal browser URL and should not be
+# translated. This string is used as a title for a file save dialog box.
+about-webrtc-save-page-dialog-title = cadw about:webrtc fel
+
+## These labels are for a disclosure which contains the information for closed PeerConnection sections
+
+about-webrtc-closed-peerconnection-disclosure-show-msg = Dangos PeerConnections Caeedig
+about-webrtc-closed-peerconnection-disclosure-hide-msg = Cuddio PeerConnections Caeedig
+
+## AEC is an abbreviation for Acoustic Echo Cancellation.
+
+about-webrtc-aec-logging-msg-label = Cofnodi AEC
+about-webrtc-aec-logging-off-state-label = Cychwyn Cofnodi AEC
+about-webrtc-aec-logging-on-state-label = Atal Cofnodi AEC
+about-webrtc-aec-logging-on-state-msg = Cofnodi AEC yn weithredol (siarad gyda'r galwr am ychydig funudau ac yna atal y cipio)
+about-webrtc-aec-logging-toggled-on-state-msg = Cofnodi AEC yn weithredol (siarad gyda'r galwr am ychydig funudau ac yna atal y cipio)
+about-webrtc-aec-logging-unavailable-sandbox = Mae angen y newidyn amgylchedd MOZ_DISABLE_CONTENT_SANDBOX=1 er mwyn allforio cofnodion AEC. Gosodwch y newidyn hwn dim ond os ydych chi'n deall y risgiau posibl.
+# Variables:
+#  $path (String) - The path to which the aec log file is saved.
+about-webrtc-aec-logging-toggled-off-state-msg = Mae'r ffeiliau cofnod y cipio yn: { $path }
+
+##
+
+# The autorefresh checkbox causes a stats section to autorefresh its content when checked
+about-webrtc-auto-refresh-label = Auto Adnewyddu
+# Determines the default state of the Auto Refresh check boxes
+about-webrtc-auto-refresh-default-label = Awto Adnewyddu Rhagosodedig
+# A button which forces a refresh of displayed statistics
+about-webrtc-force-refresh-button = Adnewyddu
+# "PeerConnection" is a proper noun associated with the WebRTC module. "ID" is
+# an abbreviation for Identifier. This string should not normally be translated
+# and is used as a data label.
+about-webrtc-peerconnection-id-label = Dynodiad PeerConnection:
+# The number of DataChannels that a PeerConnection has opened
+about-webrtc-data-channels-opened-label = Sianeli Data Agorwyd:
+# The number of once open DataChannels that a PeerConnection has closed
+about-webrtc-data-channels-closed-label = Sianeli Data Caewyd:
+
+## "SDP" is an abbreviation for Session Description Protocol, an IETF standard.
+## See http://wikipedia.org/wiki/Session_Description_Protocol
+
+about-webrtc-sdp-heading = SDP
+about-webrtc-local-sdp-heading = SDP lleol
+about-webrtc-local-sdp-heading-offer = SDP lleol (Cynnig)
+about-webrtc-local-sdp-heading-answer = SDP lleol (Ateb)
+about-webrtc-remote-sdp-heading = SDP pell
+about-webrtc-remote-sdp-heading-offer = SDP pell (Cynnig)
+about-webrtc-remote-sdp-heading-answer = SDP pell (Ateb)
+about-webrtc-sdp-history-heading = Hanes SDP
+about-webrtc-sdp-parsing-errors-heading = Gwallau Didoli SDP
+
+##
+
+# "RTP" is an abbreviation for the Real-time Transport Protocol, an IETF
+# specification, and should not normally be translated. "Stats" is an
+# abbreviation for Statistics.
+about-webrtc-rtp-stats-heading = Ystadegau RTP
+
+## "ICE" is an abbreviation for Interactive Connectivity Establishment, which
+## is an IETF protocol, and should not normally be translated.
+
+about-webrtc-ice-state = Cyflwr ICE
+# "Stats" is an abbreviation for Statistics.
+about-webrtc-ice-stats-heading = Ystadegau ICE
+about-webrtc-ice-restart-count-label = Ailgychwyn ICE:
+about-webrtc-ice-rollback-count-label = Hen fersiynau ICE:
+about-webrtc-ice-pair-bytes-sent = Didau wedi'u hanfon:
+about-webrtc-ice-pair-bytes-received = Didau wedi'u derbyn:
+about-webrtc-ice-component-id = Enw'r Cydran
+
+## These adjectives are used to label a line of statistics collected for a peer
+## connection. The data represents either the local or remote end of the
+## connection.
+
+about-webrtc-type-local = Lleol
+about-webrtc-type-remote = Pell
+
+##
+
+# This adjective is used to label a table column. Cells in this column contain
+# the localized javascript string representation of "true" or are left blank.
+about-webrtc-nominated = Enwebwyd
+# This adjective is used to label a table column. Cells in this column contain
+# the localized javascript string representation of "true" or are left blank.
+# This represents an attribute of an ICE candidate.
+about-webrtc-selected = Dewiswyd
+about-webrtc-save-page-label = Cadw Tudalen
+about-webrtc-debug-mode-msg-label = Modd Dadfygio
+about-webrtc-debug-mode-off-state-label = Cychwyn y Modd Dadfygio
+about-webrtc-debug-mode-on-state-label = Atal y Modd Dadfygio
+about-webrtc-enable-logging-label = Galluogi Rhagosodiad Cofnod WebRTC
+about-webrtc-stats-heading = Ystadegau'r Sesiwn
+about-webrtc-peerconnections-section-heading = Ystadegau RTCPeerConnection
+about-webrtc-peerconnections-section-show-msg = Dangos Ystadegau RTCPeerConnection
+about-webrtc-peerconnections-section-hide-msg = Cuddio Ystadegau RTCPeerConnection
+about-webrtc-stats-clear = Clirio Hanes
+about-webrtc-log-heading = Cofnod Cysylltu
+about-webrtc-log-clear = Clirio'r Cofnod
+about-webrtc-log-show-msg = dangos cofnod
+    .title = cliciwch i ehangu'r adran
+about-webrtc-log-hide-msg = cuddio cofnod
+    .title = cliciwch i gau'r adran
+about-webrtc-log-section-show-msg = Dangos cofnod
+    .title = Cliciwch i ehangu'r adran
+about-webrtc-log-section-hide-msg = Cuddio cofnod
+    .title = Cliciwch i gau'r adran
+about-webrtc-copy-report-button = Copïo Adroddiad
+about-webrtc-copy-report-history-button = Copïo Hanes Adroddiad
+
+## These are used to display a header for a PeerConnection.
+## Variables:
+##  $browser-id (Number) - A numeric id identifying the browser tab for the PeerConnection.
+##  $id (String) - A globally unique identifier for the PeerConnection.
+##  $url (String) - The url of the site which opened the PeerConnection.
+##  $now (Date) - The JavaScript timestamp at the time the report was generated.
+
+about-webrtc-connection-open = [ { $browser-id } | { $id } ] { $url } { $now }
+about-webrtc-connection-closed = [ { $browser-id } | { $id } ] { $url } (cau) { $now }
+
+## These are used to indicate what direction media is flowing.
+## Variables:
+##  $codecs - a list of media codecs
+
+about-webrtc-short-send-receive-direction = Anfon / Derbyn: { $codecs }
+about-webrtc-short-send-direction = Anfon: { $codecs }
+about-webrtc-short-receive-direction = Derbyn: { $codecs }
+
+##
+
+about-webrtc-local-candidate = Ymgeisydd Lleol
+about-webrtc-remote-candidate = Ymgeisydd Pell
+about-webrtc-raw-candidates-heading = Pob Ymgeisydd Bras
+about-webrtc-raw-local-candidate = Ymgeisydd Lleol Bras
+about-webrtc-raw-remote-candidate = Ymgeisydd Pell Bras
+about-webrtc-raw-cand-show-msg = dangos ymgeiswyr bras
+    .title = cliciwch i ehangu'r adran
+about-webrtc-raw-cand-hide-msg = cuddio ymgeiswyr bras
+    .title = cliciwch i gau'r adran
+about-webrtc-raw-cand-section-show-msg = Dangos ymgeiswyr bras
+    .title = Cliciwch i ehangu'r adran
+about-webrtc-raw-cand-section-hide-msg = Cuddio ymgeiswyr bras
+    .title = Cliciwch i gau'r adran
+about-webrtc-priority = Blaenoriaeth
+about-webrtc-fold-show-msg = dangos manylion
+    .title = cliciwch i ehangu'r adran
+about-webrtc-fold-hide-msg = cuddio manylion
+    .title = cliciwch i gau'r adran
+about-webrtc-fold-default-show-msg = Dangos manylion
+    .title = Cliciwch i ehangu'r adran
+about-webrtc-fold-default-hide-msg = Cuddio manylion
+    .title = Cliciwch i gau'r adran
+about-webrtc-dropped-frames-label = Fframiau wedi'u gollwng:
+about-webrtc-discarded-packets-label = Pecynnau wedi'u hepgor:
+about-webrtc-decoder-label = Datgodwyr
+about-webrtc-encoder-label = Amgodiwr
+about-webrtc-show-tab-label = Dangos tab
+about-webrtc-current-framerate-label = Cyfradd fframio
+about-webrtc-width-px = Lled (px)
+about-webrtc-height-px = Uchder (px)
+about-webrtc-consecutive-frames = Fframiau Olynol
+about-webrtc-time-elapsed = Amser wedi Pasio
+about-webrtc-estimated-framerate = Amcan o Raddfa Ffrâm
+about-webrtc-rotation-degrees = Cylchdroi (graddau)
+about-webrtc-first-frame-timestamp = Stamp Amser Derbyn y  Ffrâm Gyntaf
+about-webrtc-last-frame-timestamp = Stamp Amser Derbyn y  Ffrâm Olaf
+
+## SSRCs are identifiers that represent endpoints in an RTP stream
+
+# This is an SSRC on the local side of the connection that is receiving RTP
+about-webrtc-local-receive-ssrc = Derbyn SSRC  Lleol
+# This is an SSRC on the remote side of the connection that is sending RTP
+about-webrtc-remote-send-ssrc = Anfon SSRC o Bell
+
+## These are displayed on the button that shows or hides the
+## PeerConnection configuration disclosure
+
+about-webrtc-pc-configuration-show-msg = Dangos Ffurfweddiad
+about-webrtc-pc-configuration-hide-msg = Cuddio Ffurfwedd
+
+##
+
+# An option whose value will not be displayed but instead noted as having been
+# provided
+about-webrtc-configuration-element-provided = Wedi'i Ddarparu
+# An option whose value will not be displayed but instead noted as having not
+# been provided
+about-webrtc-configuration-element-not-provided = Heb ei Ddarparu
+# The options set by the user in about:config that could impact a WebRTC call
+about-webrtc-custom-webrtc-configuration-heading = Dewisiadau WebRTC Gosodedig y Defnyddiwr
+# The options set by the user in about:config that could impact a WebRTC call
+about-webrtc-user-modified-configuration-heading = Ffurfweddiad WebRTC wedi'i Addasu gan Ddefnyddiwr
+
+## These are displayed on the button that shows or hides the
+## user modified configuration disclosure
+
+about-webrtc-user-modified-configuration-show-msg = Dangos Ffurfweddiad Defnyddiwr Wedi'i Addasu
+about-webrtc-user-modified-configuration-hide-msg = Cuddio Ffurfweddiad Defnyddiwr Wedi'i Addasu
+
+##
+
+# Section header for estimated bandwidths of WebRTC media flows
+about-webrtc-bandwidth-stats-heading = Amcangyfrif Lled Band
+# The ID of the MediaStreamTrack
+about-webrtc-track-identifier = Dynodwr tracio
+# The estimated bandwidth available for sending WebRTC media in bytes per second
+about-webrtc-send-bandwidth-bytes-sec = Lled Band Anfon (beit/eiliad)
+# The estimated bandwidth available for receiving WebRTC media in bytes per second
+about-webrtc-receive-bandwidth-bytes-sec = Lled Band Derbyn (beit/eiliad)
+# Maximum number of bytes per second that will be padding zeros at the ends of packets
+about-webrtc-max-padding-bytes-sec = Uchafswm Padio (beit/eiliad)
+# The amount of time inserted between packets to keep them spaced out
+about-webrtc-pacer-delay-ms = Oedi Pacer ms
+# The amount of time it takes for a packet to travel from the local machine to the remote machine,
+# and then have a packet return
+about-webrtc-round-trip-time-ms = RTT ms
+# This is a section heading for video frame statistics for a MediaStreamTrack.
+# see https://developer.mozilla.org/en-US/docs/Web/API/MediaStreamTrack.
+# Variables:
+#   $track-identifier (String) - The unique identifier for the MediaStreamTrack.
+about-webrtc-frame-stats-heading = Ystadegau Ffrâm Fideo - MediaStreamTrack ID: { $track-identifier }
+
+## These are paths used for saving the about:webrtc page or log files so
+## they can be attached to bug reports.
+## Variables:
+##  $path (String) - The path to which the file is saved.
+
+about-webrtc-save-page-msg = cadwyd y dudalen i: { $path }
+about-webrtc-debug-mode-off-state-msg = mae modd canfod y cofnod olrhain yn: { $path }
+about-webrtc-debug-mode-on-state-msg = modd dadfygio'n weithredol, cofnod olrhain yn { $path }
+about-webrtc-aec-logging-off-state-msg = mae'r ffeiliau cofnod y cipio yn: { $path }
+# This path is used for saving the about:webrtc page so it can be attached to
+# bug reports.
+# Variables:
+#  $path (String) - The path to which the file is saved.
+about-webrtc-save-page-complete-msg = Cadwyd y dudalen i: { $path }
+# This is the total number of frames encoded or decoded over an RTP stream.
+# Variables:
+#  $frames (Number) - The number of frames encoded or decoded.
+about-webrtc-frames =
+    { $frames ->
+        [zero] { $frames } fframiau
+        [one] { $frames } ffrâm
+        [two] { $frames } ffrâm
+        [few] { $frames } ffrâm
+        [many] { $frames } ffrâm
+       *[other] { $frames } ffrâm
+    }
+# This is the number of audio channels encoded or decoded over an RTP stream.
+# Variables:
+#  $channels (Number) - The number of channels encoded or decoded.
+about-webrtc-channels =
+    { $channels ->
+        [zero] { $channels } sianeli
+        [one] { $channels } sianel
+        [two] { $channels } sianel
+        [few] { $channels } sianel
+        [many] { $channels } sianel
+       *[other] { $channels } sianel
+    }
+# This is the total number of packets received on the PeerConnection.
+# Variables:
+#  $packets (Number) - The number of packets received.
+about-webrtc-received-label =
+    { $packets ->
+        [zero] Heb dderbyn unrhyw becyn
+        [one] Wedi derbyn { $packets } pecyn
+        [two] Wedi derbyn { $packets } pecyn
+        [few] Wedi derbyn { $packets } pecyn
+        [many] Wedi derbyn { $packets } pecyn
+       *[other] Wedi derbyn { $packets } pecyn
+    }
+# This is the total number of packets lost by the PeerConnection.
+# Variables:
+#  $packets (Number) - The number of packets lost.
+about-webrtc-lost-label =
+    { $packets ->
+        [zero] Heb golli unrhyw becyn
+        [one] Wedi derbyn { $packets } pecyn
+        [two] Wedi derbyn { $packets } pecyn
+        [few] Wedi derbyn { $packets } pecyn
+        [many] Wedi derbyn { $packets } pecyn
+       *[other] Wedi derbyn { $packets } pecyn
+    }
+# This is the total number of packets sent by the PeerConnection.
+# Variables:
+#  $packets (Number) - The number of packets sent.
+about-webrtc-sent-label =
+    { $packets ->
+        [zero] Heb anfon unrhyw becyn
+        [one] Wedi anfon { $packets } pecyn
+        [two] Wedi anfon { $packets } pecyn
+        [few] Wedi anfon { $packets } pecyn
+        [many] Wedi anfon { $packets } pecyn
+       *[other] Wedi anfon { $packets } pecyn
+    }
+# Jitter is the variance in the arrival time of packets.
+# See: https://w3c.github.io/webrtc-stats/#dom-rtcreceivedrtpstreamstats-jitter
+# Variables:
+#   $jitter (Number) - The jitter.
+about-webrtc-jitter-label = Jitter { $jitter }
+# ICE candidates arriving after the remote answer arrives are considered trickled
+# (an attribute of an ICE candidate). These are highlighted in the ICE stats
+# table with light blue background.
+about-webrtc-trickle-caption-msg = Mae ymgeisydd diferu (yn cyrraedd ar ôl yr ateb) yn cael eu hamlygu mewn glas
+
+## "SDP" is an abbreviation for Session Description Protocol, an IETF standard.
+## See http://wikipedia.org/wiki/Session_Description_Protocol
+
+# This is used as a header for local SDP.
+# Variables:
+#  $timestamp (Number) - The Unix Epoch time at which the SDP was set.
+about-webrtc-sdp-set-at-timestamp-local = Gosod SDP lleol ar y stamp amser { NUMBER($timestamp, useGrouping: "false") }.
+# This is used as a header for remote SDP.
+# Variables:
+#  $timestamp (Number) - The Unix Epoch time at which the SDP was set.
+about-webrtc-sdp-set-at-timestamp-remote = Gosod SDP pell ar y stamp amser { NUMBER($timestamp, useGrouping: "false") }.
+# This is used as a header for an SDP section contained in two columns allowing for side-by-side comparisons.
+# Variables:
+#  $timestamp (Number) - The Unix Epoch time at which the SDP was set.
+#  $relative-timestamp (Number) - The timestamp relative to the timestamp of the earliest received SDP.
+about-webrtc-sdp-set-timestamp = Stamp amser { NUMBER($timestamp, useGrouping: "false") } (+ { $relative-timestamp } ms)
+
+## These are displayed on the button that shows or hides the SDP information disclosure
+
+about-webrtc-show-msg-sdp = Dangos SDP
+about-webrtc-hide-msg-sdp = Cuddio SDP
+
+## These are displayed on the button that shows or hides the Media Context information disclosure.
+## The Media Context is the set of preferences and detected capabilities that informs
+## the negotiated CODEC settings.
+
+about-webrtc-media-context-show-msg = Dangos Cyd-destun Cyfryngau
+about-webrtc-media-context-hide-msg = Cuddio Cyd-destun Cyfryngau
+about-webrtc-media-context-heading = Cyd-destun Cyfryngau
+
+##
+
diff --git a/thunderbird-l10n/cy/localization/cy/toolkit/about/aboutWindowsMessages.ftl b/thunderbird-l10n/cy/localization/cy/toolkit/about/aboutWindowsMessages.ftl
new file mode 100644
index 0000000000..772ba35c64
--- /dev/null
+++ b/thunderbird-l10n/cy/localization/cy/toolkit/about/aboutWindowsMessages.ftl
@@ -0,0 +1,21 @@
+# This Source Code Form is subject to the terms of the Mozilla Public
+# License, v. 2.0. If a copy of the MPL was not distributed with this
+# file, You can obtain one at http://mozilla.org/MPL/2.0/.
+
+
+### Localization for the about:windows-messages page, which is only available
+### on the Windows operating system.
+### This page records and shows messages sent from the operating system to
+### individual browser windows. These messages can be useful in debugging
+### hard-to-reproduce issues with window sizing and position.
+
+# Windows refers to the operating system
+windows-messages-page-title = Manylion Negeseuon Windows
+windows-messages-intro =
+    Mae'r dudalen hon yn dangos y negeseuon mwyaf diweddar
+    a anfonwyd gan Windows i ffenestri porwr { -brand-short-name }.
+    Mae'r mae cofnod trwm yn cynrychioli'r ffenestr hon. Sylwch fod
+    y dudalen hon yn dangos y negeseuon mwyaf diweddar ar yr adeg
+    y llwythwyd y dudalen; i weld y rhai cyfredol bydd angen i chi
+    adnewyddu'r dudalen.
+windows-messages-copy-to-clipboard = Copïo i'r clipfwrdd
diff --git a/thunderbird-l10n/cy/localization/cy/toolkit/about/abuseReports.ftl b/thunderbird-l10n/cy/localization/cy/toolkit/about/abuseReports.ftl
new file mode 100644
index 0000000000..e97e394451
--- /dev/null
+++ b/thunderbird-l10n/cy/localization/cy/toolkit/about/abuseReports.ftl
@@ -0,0 +1,116 @@
+# This Source Code Form is subject to the terms of the Mozilla Public
+# License, v. 2.0. If a copy of the MPL was not distributed with this
+# file, You can obtain one at http://mozilla.org/MPL/2.0/.
+
+# Localized string used as the dialog window title.
+# "Report" is a noun in this case, "Report for AddonName".
+#
+# Variables:
+#   $addon-name (string) - Name of the add-on being reported
+abuse-report-dialog-title = Adrodd am { $addon-name }
+abuse-report-title-extension = Adroddwch yr Estyniad hwn i { -vendor-short-name }
+abuse-report-title-sitepermission = Adroddwch ychwanegyn Caniatâd y Wefan hon i { -vendor-short-name }
+abuse-report-title-theme = Adroddwch y Thema hon i { -vendor-short-name }
+abuse-report-subtitle = Beth yw'r broblem?
+# Variables:
+#   $author-name (string) - Name of the add-on author
+abuse-report-addon-authored-by = gan <a data-l10n-name="author-name">{ $author-name }</a>
+abuse-report-learnmore =
+    Ddim yn siŵr pa fater i'w ddewis?
+    <a data-l10n-name="learnmore-link">Dysgwch fwy am adrodd ar estyniadau a themâu</a>
+abuse-report-learnmore-intro = Ddim yn siŵr pa fater i'w ddewis?
+abuse-report-learnmore-link = Dysgwch fwy am adrodd ar estyniadau a themâu
+abuse-report-submit-description = Disgrifiwch y broblem (dewisol)
+abuse-report-textarea =
+    .placeholder = Mae'n haws i ni fynd i'r afael â phroblem os oes gennym fanylion penodol. Disgrifiwch yr hyn rydych chi'n ei brofi. Diolch i chi am ein helpu i gadw'r we'n iach.
+abuse-report-submit-note =
+    Sylwer: Peidiwch â chynnwys gwybodaeth bersonol (fel enw, cyfeiriad e-bost, rhif ffôn, cyfeiriad corfforol).
+    Mae { -vendor-short-name } yn cadw cofnod parhaol o'r adroddiadau hyn.
+
+## Panel buttons.
+
+abuse-report-cancel-button = Diddymu
+abuse-report-next-button = Nesaf
+abuse-report-goback-button = Mynd nôl
+abuse-report-submit-button = Cyflwyno
+
+## Message bars descriptions.
+##
+## Variables:
+##   $addon-name (string) - Name of the add-on
+
+abuse-report-messagebar-aborted = Diddymwyd yr adroddiad ar gyfer <span data-l10n-name="addon-name">{ $addon-name }</span>>.
+abuse-report-messagebar-submitting = Anfon adroddiad ar gyfer <span data-l10n-name="addon-name">{ $addon-name }</span>.
+abuse-report-messagebar-submitted = Diolch i chi am gyflwyno adroddiad. Ydych chi am gael gwared ar <span data-l10n-name="addon-name">{ $addon-name }</span>?
+abuse-report-messagebar-submitted-noremove = Diolch am gyflwyno adroddiad.
+abuse-report-messagebar-removed-extension = Diolch i chi am gyflwyno adroddiad. Rydych wedi tynnu'r estyniad <span data-l10n-name="addon-name">{ $addon-name }</span>.
+abuse-report-messagebar-removed-sitepermission = Diolch am gyflwyno adroddiad. Rydych wedi tynnu'r estyniad <span data-l10n-name="addon-name">{ $addon-name }</span>
+abuse-report-messagebar-removed-theme = Diolch i chi am gyflwyno adroddiad. Rydych chi wedi tynnu'r thema <span data-l10n-name="addon-name">{ $addon-name }</span>
+abuse-report-messagebar-error = Roedd gwall wrth anfon yr adroddiad ar gyfer <span data-l10n-name="addon-name">{ $addon-name }</span>.
+abuse-report-messagebar-error-recent-submit = Nid yw'r adroddiad ar gyfer <span data-l10n-name="addon-name">{ $addon-name }</span> wedi ei anfon oherwydd bod adroddiad arall wedi'i gyflwyno'n ddiweddar.
+abuse-report-messagebar-aborted2 =
+    .message = Diddymwyd yr adroddiad ar gyfer { $addon-name }>.
+abuse-report-messagebar-submitting2 =
+    .message = Anfon adroddiad ar gyfer { $addon-name }.
+abuse-report-messagebar-submitted2 =
+    .message = Diolch i chi am gyflwyno adroddiad. Ydych chi am gael gwared ar { $addon-name }?
+abuse-report-messagebar-submitted-noremove2 =
+    .message = Diolch am gyflwyno adroddiad.
+abuse-report-messagebar-removed-extension2 =
+    .message = Diolch i chi am gyflwyno adroddiad. Rydych wedi tynnu'r estyniad { $addon-name }.
+abuse-report-messagebar-removed-sitepermission2 =
+    .message = Diolch am gyflwyno adroddiad. Rydych wedi tynnu'r estyniad { $addon-name }
+abuse-report-messagebar-removed-theme2 =
+    .message = Diolch i chi am gyflwyno adroddiad. Rydych chi wedi tynnu'r thema { $addon-name }
+abuse-report-messagebar-error2 =
+    .message = Roedd gwall wrth anfon yr adroddiad ar gyfer { $addon-name }.
+abuse-report-messagebar-error-recent-submit2 =
+    .message = Nid yw'r adroddiad ar gyfer { $addon-name } wedi ei anfon oherwydd bod adroddiad arall wedi'i gyflwyno'n ddiweddar.
+
+## Message bars actions.
+
+abuse-report-messagebar-action-remove-extension = Iawn, Dileu
+abuse-report-messagebar-action-keep-extension = Na, rwyf am ei gadw
+abuse-report-messagebar-action-remove-sitepermission = Iawn, Dileu
+abuse-report-messagebar-action-keep-sitepermission = Na, rwyf am ei gadw
+abuse-report-messagebar-action-remove-theme = Iawn, Dileu
+abuse-report-messagebar-action-keep-theme = Na, rwyf am ei gadw
+abuse-report-messagebar-action-retry = Ceisio eto
+abuse-report-messagebar-action-cancel = Diddymu
+
+## Abuse report reasons (optionally paired with related examples and/or suggestions)
+
+abuse-report-damage-reason-v2 = Fe wnaeth niweidio fy nghyfrifiadur neu gyfaddawdu ar fy nata
+abuse-report-damage-example = Enghraifft: Chwistrellu data maleisus neu ddata wedi'i ddwyn
+abuse-report-spam-reason-v2 = Mae'n cynnwys sbam neu'n mewnosod hysbysebu dieisiau
+abuse-report-spam-example = Enghraifft: Mewnosod hysbysebion ar dudalennau gwe
+abuse-report-settings-reason-v2 = Newidiodd fy mheiriant chwilio, hafan, neu dab newydd heb roi gwybod na gofyn imi
+abuse-report-settings-suggestions = Cyn adrodd ar yr estyniad, gallwch roi cynnig ar newid eich gosodiadau:
+abuse-report-settings-suggestions-search = Newid eich gosodiadau chwilio rhagosodedig
+abuse-report-settings-suggestions-homepage = Newidiwch eich tudalen cartref a'ch tab newydd
+abuse-report-deceptive-reason-v2 = Mae'n honni ei fod yn rhywbeth nad ydyw
+abuse-report-deceptive-example = Enghraifft: Disgrifiad neu ddelweddau camarweiniol
+abuse-report-broken-reason-extension-v2 = Nid yw'n gweithio, mae'n torri gwefannau, neu'n arafu { -brand-product-name }
+abuse-report-broken-reason-sitepermission-v2 = Nid yw'n gweithio, mae'n torri gwefannau, neu'n arafu { -brand-product-name }
+abuse-report-broken-reason-theme-v2 = Nid yw'n gweithio nac yn torri dangosydd y porwr
+abuse-report-broken-example = Enghraifft: Mae nodwedd yn araf, yn anodd ei defnyddio, neu ddim yn gweithio; ni fydd rhannau o wefannau yn llwytho neu'n edrych yn rhyfedd
+abuse-report-broken-suggestions-extension =
+    Mae'n edrych fel eich bod wedi adnabod gwall. Yn ogystal â chyflwyno adroddiad yma, y ffordd orau
+    orau i ddatrys mater ymarferoldeb wedi'i ddatrys yw cysylltu â datblygwr yr estyniad.
+    <a data-l10n-name="support-link">Ewch i wefan yr estyniad</a> i gael gwybodaeth gan y datblygwr.
+abuse-report-broken-suggestions-sitepermission =
+    Mae'n edrych fel eich bod wedi adnabod gwall. Yn ogystal â chyflwyno adroddiad yma, y ffordd orau
+    orau i ddatrys mater ymarferoldeb wedi'i ddatrys yw cysylltu â datblygwr y wefan.
+    <a data-l10n-name="support-link">Ewch i'r wefan</a> i gael manylion y datblygwr.
+abuse-report-broken-suggestions-theme =
+    Mae'n edrych fel eich bod wedi adnabod gwall. Yn ogystal â chyflwyno adroddiad yma, y ffordd orau
+    orau i ddatrys mater ymarferoldeb wedi'i ddatrys yw cysylltu â datblygwr y thema.
+    <a data-l10n-name="support-link"> Ewch i wefan y thema </a> i gael gwybodaeth y datblygwr.
+abuse-report-policy-reason-v2 = Mae'n cynnwys cynnwys atgas, treisgar neu anghyfreithlon
+abuse-report-policy-suggestions =
+    Sylw: Rhaid rhoi gwybod am faterion hawlfraint a nod masnach mewn proses ar wahân.
+    <a data-l10n-name="report-infringement-link"> Defnyddiwch y cyfarwyddiadau hyn</a> i
+    adrodd am y broblem.
+abuse-report-unwanted-reason-v2 = Doeddwn i erioed ei eisiau ac nid wyf yn gwybod sut i gael gwared arno
+abuse-report-unwanted-example = Enghraifft: Gosodwyd y rhaglen heb fy nghaniatâd
+abuse-report-other-reason = Rhywbeth arall
diff --git a/thunderbird-l10n/cy/localization/cy/toolkit/about/certviewer.ftl b/thunderbird-l10n/cy/localization/cy/toolkit/about/certviewer.ftl
new file mode 100644
index 0000000000..5185734a82
--- /dev/null
+++ b/thunderbird-l10n/cy/localization/cy/toolkit/about/certviewer.ftl
@@ -0,0 +1,122 @@
+# This Source Code Form is subject to the terms of the Mozilla Public
+# License, v. 2.0. If a copy of the MPL was not distributed with this
+# file, You can obtain one at http://mozilla.org/MPL/2.0/.
+
+certificate-viewer-certificate-section-title = Tystysgrif
+
+## Error messages
+
+certificate-viewer-error-message = Nid oeddem yn gallu dod o hyd i fanylion y dystysgrif, neu mae'r dystysgrif yn llygredig. Ceisiwch eto.
+certificate-viewer-error-title = Aeth rhywbeth o'i le.
+
+## Certificate information labels
+
+certificate-viewer-algorithm = Algorithm
+certificate-viewer-certificate-authority = Awdurdod Tystysgrif
+certificate-viewer-cipher-suite = Casgliad Seiffr
+certificate-viewer-common-name = Enw Cyffredin
+certificate-viewer-email-address = Cyfeiriad E-bost
+# Variables:
+#   $firstCertName (String) - Common Name for the displayed certificate
+certificate-viewer-tab-title = Tystysgrif ar gyfer { $firstCertName }
+# Inc. means Incorporated, e.g GitHub is incorporated in Delaware
+certificate-viewer-inc-country = Gwlad Corfforedig
+certificate-viewer-country = Gwlad
+certificate-viewer-curve = Cromlin
+certificate-viewer-distribution-point = Pwynt Dosbarthu
+certificate-viewer-dns-name = Enw DNS
+certificate-viewer-ip-address = Cyfeiriad IP
+certificate-viewer-other-name = Enw Arall
+certificate-viewer-exponent = Esbonydd
+certificate-viewer-id = ID
+certificate-viewer-key-exchange-group = Grŵp Cyfnewid Allwedd
+certificate-viewer-key-id = ID Allwedd
+certificate-viewer-key-size = Maint Allwedd
+# Inc. means Incorporated, e.g GitHub is incorporated in Delaware
+certificate-viewer-inc-locality = Ardal Corffori
+certificate-viewer-locality = Lleoliad
+certificate-viewer-location = Lleoliad
+certificate-viewer-logid = ID Cofnod
+certificate-viewer-method = Dull
+certificate-viewer-modulus = Modwlws
+certificate-viewer-name = Enw
+certificate-viewer-not-after = Nid ar Ôl
+certificate-viewer-not-before = Nid Cyn
+certificate-viewer-organization = Corff
+certificate-viewer-organizational-unit = Uned Corff
+certificate-viewer-policy = Polisi
+certificate-viewer-protocol = Protocol
+certificate-viewer-public-value = Gwerth Cyhoeddus
+certificate-viewer-purposes = Pwrpasau
+certificate-viewer-qualifier = Cymhwyster
+certificate-viewer-qualifiers = Cymhwysterau
+certificate-viewer-required = Gofynnol
+certificate-viewer-unsupported = &lt;heb ei gynnal&gt;
+# Inc. means Incorporated, e.g GitHub is incorporated in Delaware
+certificate-viewer-inc-state-province = Corfforedig Talaith/Ardal
+certificate-viewer-state-province = Talaith/Ardal
+certificate-viewer-sha-1 = SHA-1
+certificate-viewer-sha-256 = SHA-256
+certificate-viewer-serial-number = Rhif Cyfresol
+certificate-viewer-signature-algorithm = Algorithm Llofnod
+certificate-viewer-signature-scheme = Cynllun Llofnod
+certificate-viewer-timestamp = Stamp Amser
+certificate-viewer-value = Gwerth
+certificate-viewer-version = Fersiwn
+certificate-viewer-business-category = Categori Busnes
+certificate-viewer-subject-name = Enw'r Pwnc
+certificate-viewer-issuer-name = Enw Cyhoeddwr
+certificate-viewer-validity = Dilysrwydd
+certificate-viewer-subject-alt-names = Enwau Alt Pwnc
+certificate-viewer-public-key-info = Manylion Allweddol Cyhoeddus
+certificate-viewer-miscellaneous = Amrywiol
+certificate-viewer-fingerprints = Bysbrintiau
+certificate-viewer-basic-constraints = Cyfyngiadau Sylfaenol
+certificate-viewer-key-usages = Defnyddiau Allweddol
+certificate-viewer-extended-key-usages = Defnydd Allwedd Estynedig
+certificate-viewer-ocsp-stapling = Strapio OCSP
+certificate-viewer-subject-key-id = ID Allwedd Pwnc
+certificate-viewer-authority-key-id = ID Allwedd yr Awdurdod
+certificate-viewer-authority-info-aia = Manylion yr Awdurdod (AIA)
+certificate-viewer-certificate-policies = Polisïau Tystysgrif
+certificate-viewer-embedded-scts = SCTs mewnblanedig
+certificate-viewer-crl-endpoints = Diweddbwynt CRL
+
+# This message is used as a row header in the Miscellaneous section.
+# The associated data cell contains links to download the certificate.
+certificate-viewer-download = Llwytho i lawr
+# This message is used to replace boolean values (true/false) in several certificate fields, e.g. Certificate Authority
+# Variables:
+#   $boolean (String) - true/false value for the specific field
+certificate-viewer-boolean =
+    { $boolean ->
+        [true] Iawn
+       *[false] na
+    }
+
+## Variables:
+##   $fileName (String) - The file name to save the PEM data in, derived from the common name from the certificate being displayed.
+
+certificate-viewer-download-pem = PEM (tystysgrif)
+    .download = { $fileName }.pem
+certificate-viewer-download-pem-chain = PEM (cadwyn)
+    .download = { $fileName }-chain.pem
+
+# The title attribute for Critical Extension icon
+certificate-viewer-critical-extension =
+    .title = Mae'r estyniad hwn wedi'i nodi fel un hanfodol, sy'n golygu bod yn rhaid i gleientiaid wrthod y dystysgrif os nad ydyn nhw'n ei deall.
+certificate-viewer-export = Allforio
+    .download = { $fileName }.pem
+
+##
+
+# Label for a tab where we haven't found a better label:
+certificate-viewer-unknown-group-label = (anhysbys)
+
+## Labels for tabs displayed in stand-alone about:certificate page
+
+certificate-viewer-tab-mine = Eich Tystysgrifau
+certificate-viewer-tab-people = Pobl
+certificate-viewer-tab-servers = Gweinyddion
+certificate-viewer-tab-ca = Awdurdodau
+certificate-viewer-tab-unkonwn = Anhysbys
diff --git a/thunderbird-l10n/cy/localization/cy/toolkit/about/config.ftl b/thunderbird-l10n/cy/localization/cy/toolkit/about/config.ftl
new file mode 100644
index 0000000000..7c040f4cd4
--- /dev/null
+++ b/thunderbird-l10n/cy/localization/cy/toolkit/about/config.ftl
@@ -0,0 +1,55 @@
+# This Source Code Form is subject to the terms of the Mozilla Public
+# License, v. 2.0. If a copy of the MPL was not distributed with this
+# file, You can obtain one at http://mozilla.org/MPL/2.0/.
+
+
+## These strings appear on the warning you see when first visiting about:config.
+
+about-config-intro-warning-title = Byddwch Ofalus
+about-config-intro-warning-text = Gall newid dewisiadau ffurfweddiad uwch effeithio ar berfformiad neu ddiogelwch { -brand-short-name }.
+about-config-intro-warning-checkbox = Rhybuddiwch fi pan fyddaf yn ceisio mynd at y dewisiadau hyn
+about-config-intro-warning-button = Derbyn y Perygl a Pharhau
+
+##
+
+# This is shown on the page before searching but after the warning is accepted.
+about-config-caution-text = Gall newid dewisiadau ffurfweddiad uwch effeithio ar berfformiad neu ddiogelwch { -brand-short-name }.
+
+about-config-page-title = Dewisiadau Uwch
+
+about-config-search-input1 =
+    .placeholder = Enw dewis chwilio
+about-config-show-all = Dangos Popeth
+
+about-config-show-only-modified = Dangos dewisiadau wedi'u haddasu yn unig
+
+about-config-pref-add-button =
+    .title = Ychwanegu
+about-config-pref-toggle-button =
+    .title = Toglo
+about-config-pref-edit-button =
+    .title = Golygu
+about-config-pref-save-button =
+    .title = Cadw
+about-config-pref-reset-button =
+    .title = Ailosod
+about-config-pref-delete-button =
+    .title = Dileu
+
+## Labels for the type selection radio buttons shown when adding preferences.
+
+about-config-pref-add-type-boolean = Boole
+about-config-pref-add-type-number = Rhif
+about-config-pref-add-type-string = Llinyn
+
+## Preferences with a non-default value are differentiated visually, and at the
+## same time the state is made accessible to screen readers using an aria-label
+## that won't be visible or copied to the clipboard.
+##
+## Variables:
+##   $value (String): The full value of the preference.
+
+about-config-pref-accessible-value-default =
+    .aria-label = { $value } (default)
+about-config-pref-accessible-value-custom =
+    .aria-label = { $value } (custom)
diff --git a/thunderbird-l10n/cy/localization/cy/toolkit/about/url-classifier.ftl b/thunderbird-l10n/cy/localization/cy/toolkit/about/url-classifier.ftl
new file mode 100644
index 0000000000..e48a4e996f
--- /dev/null
+++ b/thunderbird-l10n/cy/localization/cy/toolkit/about/url-classifier.ftl
@@ -0,0 +1,58 @@
+# This Source Code Form is subject to the terms of the Mozilla Public
+# License, v. 2.0. If a copy of the MPL was not distributed with this
+# file, You can obtain one at http://mozilla.org/MPL/2.0/.
+
+url-classifier-title = Manylion Dosbarthu URL
+url-classifier-search-title = Chwilio
+url-classifier-search-result-title = Canlyniadau
+url-classifier-search-result-uri = URI: { $uri }
+url-classifier-search-result-list = Rhestr tablau: { $list }
+url-classifier-search-input = URL
+url-classifier-search-error-invalid-url = URL annilys
+url-classifier-search-error-no-features = Heb ddewis nodwedd
+url-classifier-search-btn = Cychwyn chwilio
+url-classifier-search-features = Nodweddion
+url-classifier-search-listType = Math o restr
+url-classifier-provider-title = Darparwr
+url-classifier-provider = Darparwr
+url-classifier-provider-last-update-time = Amser y diweddariad diwethaf
+url-classifier-provider-next-update-time = Amser y diweddariad nesaf
+url-classifier-provider-back-off-time = Amser atal
+url-classifier-provider-last-update-status = Statws y diweddariad diwethaf
+url-classifier-provider-update-btn = Diweddaru
+url-classifier-cache-title = Storfa Dros Dro
+url-classifier-cache-refresh-btn = Adnewyddu
+url-classifier-cache-clear-btn = Clirio
+url-classifier-cache-table-name = Enw tabl
+url-classifier-cache-ncache-entries = Nifer o gofnodion storfa dros dro negyddol
+url-classifier-cache-pcache-entries = Nifer o gofnodion storfa dros dro negyddol
+url-classifier-cache-show-entries = Dangos y cofnodion
+url-classifier-cache-entries = Cofnodion Storfa Dros Dro
+url-classifier-cache-prefix = Rhagddodiad
+url-classifier-cache-ncache-expiry = Storfa dros dro negyddol yn dod i ben
+url-classifier-cache-fullhash = Hash llawn
+url-classifier-cache-pcache-expiry = Storfa dros dro positif yn dod i ben
+url-classifier-debug-title = Dadfygio
+url-classifier-debug-module-btn = Gosod Modiwlau Cofnodi
+url-classifier-debug-file-btn = Gosod Ffeil Cofnodi
+url-classifier-debug-js-log-chk = Gosod Cofnod JS
+url-classifier-debug-sb-modules = Modiwlau cofnodi Pori Diogel
+url-classifier-debug-modules = Y modiwlau cofnodi cyfredol
+url-classifier-debug-sbjs-modules = Cofnod Pori Diogel JS
+url-classifier-debug-file = Ffeil cofnod cyfredol
+
+url-classifier-trigger-update = Diweddariad Triger
+url-classifier-not-available = Dim Ar Gael
+url-classifier-disable-sbjs-log = Analluogi Cofnod JS Pori Diogel
+url-classifier-enable-sbjs-log = Galluogi Cofnod JS Pori Diogel
+url-classifier-enabled = Galluogwyd
+url-classifier-disabled = Analluogwyd
+url-classifier-updating = diweddaru
+url-classifier-cannot-update = methu diweddaru
+url-classifier-success = llwyddiant
+
+## Variables
+##   $error (string) - Error message
+
+url-classifier-update-error = gwall diweddaru ({ $error })
+url-classifier-download-error = gwall llwytho i lawr ({ $error })
diff --git a/thunderbird-l10n/cy/localization/cy/toolkit/branding/accounts.ftl b/thunderbird-l10n/cy/localization/cy/toolkit/branding/accounts.ftl
new file mode 100644
index 0000000000..1dc6d58608
--- /dev/null
+++ b/thunderbird-l10n/cy/localization/cy/toolkit/branding/accounts.ftl
@@ -0,0 +1,7 @@
+# This Source Code Form is subject to the terms of the Mozilla Public
+# License, v. 2.0. If a copy of the MPL was not distributed with this
+# file, You can obtain one at http://mozilla.org/MPL/2.0/.
+
+# “Account” can be localized, “Firefox” must be treated as a brand,
+# and kept in English.
+-fxaccount-brand-name = Cyfrif Firefox
diff --git a/thunderbird-l10n/cy/localization/cy/toolkit/branding/brandings.ftl b/thunderbird-l10n/cy/localization/cy/toolkit/branding/brandings.ftl
new file mode 100644
index 0000000000..af0f8b32fd
--- /dev/null
+++ b/thunderbird-l10n/cy/localization/cy/toolkit/branding/brandings.ftl
@@ -0,0 +1,45 @@
+# This Source Code Form is subject to the terms of the Mozilla Public
+# License, v. 2.0. If a copy of the MPL was not distributed with this
+# file, You can obtain one at http://mozilla.org/MPL/2.0/.
+
+
+## The following feature names must be treated as a brand.
+##
+## They cannot be:
+## - Transliterated.
+## - Translated.
+##
+## Declension should be avoided where possible, leaving the original
+## brand unaltered in prominent UI positions.
+##
+## For further details, consult:
+## https://mozilla-l10n.github.io/styleguides/mozilla_general/#brands-copyright-and-trademark
+
+-facebook-container-brand-name = Facebook Container
+-lockwise-brand-name = Firefox Lockwise
+-lockwise-brand-short-name = Lockwise
+-monitor-brand-name = Firefox Monitor
+-monitor-brand-short-name = Monitor
+-pocket-brand-name = Pocket
+-send-brand-name = Firefox Send
+-screenshots-brand-name = Firefox Screenshots
+-mozilla-vpn-brand-name = Mozilla VPN
+-profiler-brand-name = Firefox Profiler
+-translations-brand-name = Firefox Translations
+-focus-brand-name = Firefox Focus
+-relay-brand-name = Firefox Relay
+-relay-brand-short-name = Relay
+-fakespot-brand-name = Fakespot
+# Note the name of the website is capitalized.
+-fakespot-website-name = Fakespot.com
+# The particle "by" can be localized, "Fakespot" and "Mozilla" should not be localized or transliterated.
+-fakespot-brand-full-name = Fakespot gan Mozilla
+# “Suggest” can be localized, “Firefox” must be treated as a brand
+# and kept in English.
+-firefox-suggest-brand-name = Awgrymadau Firefox
+# ”Home" can be localized, “Firefox” must be treated as a brand
+# and kept in English.
+-firefox-home-brand-name = Cartref Firefox
+# View" can be localized, “Firefox” must be treated as a brand
+# and kept in English.
+-firefoxview-brand-name = Cipolwg Firefox
diff --git a/thunderbird-l10n/cy/localization/cy/toolkit/contentanalysis/contentanalysis.ftl b/thunderbird-l10n/cy/localization/cy/toolkit/contentanalysis/contentanalysis.ftl
new file mode 100644
index 0000000000..3a048e17d4
--- /dev/null
+++ b/thunderbird-l10n/cy/localization/cy/toolkit/contentanalysis/contentanalysis.ftl
@@ -0,0 +1,31 @@
+# This Source Code Form is subject to the terms of the Mozilla Public
+# License, v. 2.0. If a copy of the MPL was not distributed with this
+# file, You can obtain one at http://mozilla.org/MPL/2.0/.
+
+contentanalysis-alert-title = Dadansoddi Cynnwys
+# Variables:
+#   $content - Description of the content being warned about, such as "clipboard" or "aFile.txt"
+contentanalysis-slow-agent-notification = Mae'r teclyn Dadansoddi Cynnwys yn cymryd amser hir i ymateb ynghylch adnodd “{ $content }”
+contentanalysis-slow-agent-dialog-title = Wrthi'n dadansoddi cynnwys
+# Variables:
+#   $content - Description of the content being warned about, such as "clipboard" or "aFile.txt"
+contentanalysis-slow-agent-dialog-body = Mae Dadansoddi Cynnwys yn dadansoddi adnodd “{ $content }”
+contentanalysis-operationtype-clipboard = clipfwrdd
+contentanalysis-operationtype-dropped-text = testun wedi'i ostwng
+contentanalysis-warndialogtitle = Gall y cynnwys hwn fod yn anniogel
+# Variables:
+#   $content - Description of the content being warned about, such as "clipboard" or "aFile.txt"
+contentanalysis-warndialogtext = Mae eich sefydliad yn defnyddio meddalwedd atal colli data sydd wedi nodi bod y cynnwys hwn yn anniogel: { $content }. Ei ddefnyddio beth bynnag?
+contentanalysis-warndialog-response-allow = Defnyddio'r cynnwys
+contentanalysis-warndialog-response-deny = Diddymu
+contentanalysis-notification-title = Dadansoddi Cynnwys
+# Variables:
+#   $content - Description of the content being reported, such as "clipboard" or "aFile.txt"
+#   $response - The response received from the content analysis agent, such as "REPORT_ONLY"
+contentanalysis-genericresponse-message = Ymatebodd Dadansoddi Cynnwys gyda { $response } am adnodd: { $content }
+# Variables:
+#   $content - Description of the content being blocked, such as "clipboard" or "aFile.txt"
+contentanalysis-block-message = Mae eich sefydliad yn defnyddio meddalwedd atal colli data sydd wedi rhwystro'r cynnwys hwn: { $content }.
+# Variables:
+#   $content - Description of the content being blocked, such as "clipboard" or "aFile.txt"
+contentanalysis-error-message = Digwyddodd gwall wrth gyfathrebu â'r feddalwedd atal colli data. Gwrthodwyd trosglwyddo adnodd: { $content }.
diff --git a/thunderbird-l10n/cy/localization/cy/toolkit/downloads/downloadUI.ftl b/thunderbird-l10n/cy/localization/cy/toolkit/downloads/downloadUI.ftl
new file mode 100644
index 0000000000..e70c09fe3a
--- /dev/null
+++ b/thunderbird-l10n/cy/localization/cy/toolkit/downloads/downloadUI.ftl
@@ -0,0 +1,51 @@
+# This Source Code Form is subject to the terms of the Mozilla Public
+# License, v. 2.0. If a copy of the MPL was not distributed with this
+# file, You can obtain one at http://mozilla.org/MPL/2.0/.
+
+download-ui-confirm-title = Diddymu Pob Llwyth?
+
+## Variables:
+##   $downloadsCount (Number): The current downloads count.
+
+download-ui-confirm-quit-cancel-downloads =
+    { $downloadsCount ->
+        [1] Os fyddwch yn gadael, bydd 1 llwyth yn cael ei ddiddymu. Ydych chi'n siŵr eich bod am adael?
+       *[other] Os fyddwch yn gadael, bydd { $downloadsCount } llwyth yn cael eu diddymu. Ydych chi'n siŵr eich bod am adael?
+    }
+download-ui-confirm-quit-cancel-downloads-mac =
+    { $downloadsCount ->
+        [1] Os fyddwch yn gadael, bydd 1 llwyth yn cael ei ddiddymu. Ydych chi'n siŵr eich bod am adael?
+       *[other] Os fyddwch yn gadael, bydd { $downloadsCount } llwyth yn cael eu diddymu. Ydych chi'n siŵr eich bod am adael?
+    }
+download-ui-dont-quit-button =
+    { PLATFORM() ->
+        [mac] Peidio Gorffen
+       *[other] Peidio Gadael
+    }
+
+download-ui-confirm-offline-cancel-downloads =
+    { $downloadsCount ->
+        [1] Os fyddwch yn mynd all-lein, bydd 1 llwyth yn cael ei ddiddymu. Ydych chi'n siŵr eich bod am fynd all-lein?
+       *[other] Os fyddwch yn mynd all-lein, bydd { $downloadsCount } llwyth yn cael eu diddymu. Ydych chi'n siŵr eich bod am fynd all-lein?
+    }
+download-ui-dont-go-offline-button = Aros Ar-lein
+
+download-ui-confirm-leave-private-browsing-windows-cancel-downloads =
+    { $downloadsCount ->
+        [1] Os ydych yn cau pob ffenestr Pori Preifat nawr, bydd 1 llwyth yn cael ei ddiddymu. Ydych chi'n siŵr eich bod am adael y modd Pori Preifat?
+       *[other] Os ydych yn cau pob ffenestr Pori Preifat nawr, bydd { $downloadsCount } llwyth yn cael eu diddymu. Ydych chi'n siŵr eich bod am adael y modd Pori Preifat?
+    }
+download-ui-dont-leave-private-browsing-button = Aros yn y Modd Pori Preifat
+
+download-ui-cancel-downloads-ok =
+    { $downloadsCount ->
+        [1] Diddymu 1 Llwyth
+       *[other] Diddymu { $downloadsCount } Llwyth
+    }
+
+##
+
+download-ui-file-executable-security-warning-title = Agor Ffeil Gweithredadwy?
+# Variables:
+#   $executable (String): The executable file to be opened.
+download-ui-file-executable-security-warning = Mae "{ $executable }" yn ffeil weithredadwy. Gall ffeiliau gweithredadwy gynnwys firysau neu god maleisus arall gall ddifrodi eich cyfrifiadur. Byddwch ofalus wrth agor y ffeil. Ydych chi'n siŵr eich bod am agor "{ $executable }"?
diff --git a/thunderbird-l10n/cy/localization/cy/toolkit/downloads/downloadUtils.ftl b/thunderbird-l10n/cy/localization/cy/toolkit/downloads/downloadUtils.ftl
new file mode 100644
index 0000000000..9c1e651d18
--- /dev/null
+++ b/thunderbird-l10n/cy/localization/cy/toolkit/downloads/downloadUtils.ftl
@@ -0,0 +1,122 @@
+# This Source Code Form is subject to the terms of the Mozilla Public
+# License, v. 2.0. If a copy of the MPL was not distributed with this
+# file, You can obtain one at http://mozilla.org/MPL/2.0/.
+
+## Variables:
+## $timeValue (number) - Number of units of time
+
+# Short form for seconds
+download-utils-short-seconds =
+    { $timeValue ->
+        [zero] e
+        [one] e
+        [two] e
+        [few] e
+        [many] e
+       *[other] e
+    }
+# Short form for minutes
+download-utils-short-minutes =
+    { $timeValue ->
+        [zero] m
+        [one] m
+        [two] m
+        [few] m
+        [many] m
+       *[other] m
+    }
+# Short form for hours
+download-utils-short-hours =
+    { $timeValue ->
+        [zero] a
+        [one] a
+        [two] a
+        [few] a
+        [many] a
+       *[other] a
+    }
+# Short form for days
+download-utils-short-days =
+    { $timeValue ->
+        [zero] d
+        [one] d
+        [two] d
+        [few] d
+        [many] d
+       *[other] d
+    }
+
+##
+
+# — is the "em dash" (long dash)
+# example: 4 minutes left — 1.1 of 11.1 GB (2.2 MB/sec)
+# Variables:
+#   $timeLeft (String): time left.
+#   $transfer (String): transfer progress.
+#   $rate (String): rate number.
+#   $unit (String): rate unit.
+download-utils-status = { $timeLeft } — { $transfer } ({ $rate } { $unit }/sec)
+# If download speed is a JavaScript Infinity value, this phrase is used
+# — is the "em dash" (long dash)
+# example: 4 minutes left — 1.1 of 11.1 GB (Really fast)
+# Variables:
+#   $timeLeft (String): time left.
+#   $transfer (String): transfer progress.
+download-utils-status-infinite-rate = { $timeLeft } — { $transfer } (Cyflym iawn)
+# — is the "em dash" (long dash)
+# example: 4 minutes left — 1.1 of 11.1 GB
+# Variables:
+#   $timeLeft (String): time left.
+#   $transfer (String): transfer progress.
+download-utils-status-no-rate = { $timeLeft } — { $transfer }
+
+download-utils-bytes = beit
+download-utils-kilobyte = KB
+download-utils-megabyte = MB
+download-utils-gigabyte = GB
+
+# example: 1.1 of 333 MB
+# Variables:
+#   $progress (String): progress number.
+#   $total (String): total number.
+#   $totalUnits (String): total unit.
+download-utils-transfer-same-units = { $progress } o { $total } { $totalUnits }
+# example: 11.1 MB of 3.3 GB
+# Variables:
+#   $progress (String): progress number.
+#   $progressUnits (String): progress unit.
+#   $total (String): total number.
+#   $totalUnits (String): total unit.
+download-utils-transfer-diff-units = { $progress } { $progressUnits } o { $total } { $totalUnits }
+# example: 111 KB
+# Variables:
+#   $progress (String): progress number.
+#   $progressUnits (String): unit.
+download-utils-transfer-no-total = { $progress } { $progressUnits }
+
+# examples: 1m; 11h
+# Variables:
+#   $time (String): time number.
+#   $unit (String): time unit.
+download-utils-time-pair = { $time } { $unit }
+# examples: 1m left; 11h left
+# Variables:
+#   $time (String): time left, including a unit
+download-utils-time-left-single = { $time } ar ôl
+# examples: 11h 2m left; 1d 22h left
+# Variables:
+#   $time1 (String): time left, including a unit
+#   $time2 (String): smaller measure of time left, including a unit
+download-utils-time-left-double = { $time1 } { $time2 } ar ôl
+download-utils-time-few-seconds = Ychydig eiliadau ar ôl
+download-utils-time-unknown = Amser anhysbys ar ôl
+
+# Variables:
+#   $scheme (String): URI scheme like data: jar: about:
+download-utils-done-scheme = Adnodd { $scheme }
+# Special case of done-scheme for file:
+# This is used as an eTLD replacement for local files, so make it lower case
+download-utils-done-file-scheme = ffeil leol
+
+# Displayed time for files finished yesterday
+download-utils-yesterday = Ddoe
diff --git a/thunderbird-l10n/cy/localization/cy/toolkit/featuregates/features.ftl b/thunderbird-l10n/cy/localization/cy/toolkit/featuregates/features.ftl
new file mode 100644
index 0000000000..b77c04ce66
--- /dev/null
+++ b/thunderbird-l10n/cy/localization/cy/toolkit/featuregates/features.ftl
@@ -0,0 +1,58 @@
+# This Source Code Form is subject to the terms of the Mozilla Public
+# License, v. 2.0. If a copy of the MPL was not distributed with this
+# file, You can obtain one at http://mozilla.org/MPL/2.0/.
+
+# The title of the experiment should be kept in English as it may be referenced
+# by various online articles and is technical in nature.
+experimental-features-css-masonry2 =
+    .label = CSS: Masonry Layout
+experimental-features-css-masonry-description = Yn galluogi cefnogaeth i nodwedd arbrofol Cynllun Masonry CSS. Gw. yr <a data-l10n-name="explainer">esboniwr</a> i gael disgrifiad lefel uchel o'r nodwedd. I ddarparu adborth, rhowch sylwadau yn <a data-l10n-name="w3c-issue">y mater GitHub hwn</a> neu <a data-l10n-name="bug">y byg hwn</a>.
+
+# The title of the experiment should be kept in English as it may be referenced
+# by various online articles and is technical in nature.
+experimental-features-web-gpu2 =
+    .label = Web API: WebGPU
+experimental-features-web-gpu-description3 = Mae <a data-l10n-name="wikipedia-webgpu">WebGPU API</a> yn darparu cymorth lefel isel ar gyfer cyflawni rendrad cyfrifiant a graffeg gan ddefnyddio'r <a data-l10n-name="wikipedia-gpu">Prosesu Graffeg Uned (GPU)</a> o ddyfais neu gyfrifiadur y defnyddiwr. Mae fersiwn cyntaf y <a data-l10n-name="spec">fanyleb</a> bron â chael ei gwblhau. Gweler <a data-l10n-name="bugzilla">bug 1616739</a> am ragor o fanylion.
+
+# The title of the experiment should be kept in English as it may be referenced
+# by various online articles and is technical in nature.
+experimental-features-media-jxl =
+    .label = Cyfryngau: JPEG XL
+experimental-features-media-jxl-description = Gyda'r nodwedd hon wedi'i galluogi, mae { -brand-short-name } yn cefnogi fformat JPEG XL (JXL). Mae hwn yn fformat ffeil delwedd amgen sy'n cefnogi trosglwyddo  heb golled o ffeiliau JPEG traddodiadol. Darllenwch <a data-l10n-name="bugzilla">bug 1539075</a> am ragor o fanylion.
+
+experimental-features-devtools-compatibility-panel =
+    .label = Developer Tools: Compatibility Panel
+experimental-features-devtools-compatibility-panel-description = Panel ochr ar gyfer yr Arolygydd Tudalen sy'n dangos gwybodaeth i chi sy'n manylu ar statws cydnawsedd traws-borwr eich ap. Gweler <a data-l10n-name="bugzilla">bug 1584464</a> am fwy o fanylion.
+
+
+# Do not translate 'SameSite', 'Lax' and 'None'.
+experimental-features-cookie-samesite-none-requires-secure2 =
+    .label = Cwcis: mae SameSite=none angen priodoledd ddiogel
+experimental-features-cookie-samesite-none-requires-secure2-description = Mae cwcis â phriodoledd “SameSite=None” angen y briodoledd ddiogel. Mae'r nodwedd hon yn gofyn am “Cookies: SameSite=Lax by default”.
+
+# about:home should be kept in English, as it refers to the the URI for
+# the internal default home page.
+experimental-features-abouthome-startup-cache =
+    .label = about:home startup cache
+experimental-features-abouthome-startup-cache-description = Storfa ar gyfer y ddogfen gychwynnol about:home sy'n cael ei llwytho yn ragosodedig wrth gychwyn. Pwrpas y storfa yw gwella perfformiad cychwyn.
+
+# "Service Worker" is an API name and is usually not translated.
+experimental-features-devtools-serviceworker-debugger-support =
+    .label = Developer Tools: Service Worker debugging
+# "Service Worker" is an API name and is usually not translated.
+experimental-features-devtools-serviceworker-debugger-support-description = Yn galluogi cefnogaeth arbrofol i Weithwyr Gwasanaeth yn y panel Dadfygiwr. Efallai y bydd y nodwedd hon yn arafu'r Offer Datblygwr ac yn cynyddu'r defnydd o gof.
+
+# WebRTC global mute toggle controls
+experimental-features-webrtc-global-mute-toggles =
+    .label = Toglau Tewi WebRTC Cyffredinol
+experimental-features-webrtc-global-mute-toggles-description = Ychwanegwch ffyrdd o reoli dangosydd rhannu WebRTC i gyd sy'n caniatáu i ddefnyddwyr dewi eu llif meicroffon a chamera.
+
+# JS JIT Warp project
+experimental-features-js-warp =
+    .label = JavaScript JIT: Warp
+experimental-features-js-warp-description = Galluogi Warp, project i wella perfformiad JavaScript a defnydd o'r cof.
+
+# Search during IME
+experimental-features-ime-search =
+    .label = Bar Cyfeiriadau: dangos canlyniadau wrth ddefnyddio'r IME
+experimental-features-ime-search-description = Offeryn yw IME (Golygydd Dull Mewnbwn) sy'n eich galluogi i nodi symbolau cymhleth, fel y rhai sy'n cael eu ddefnyddio mewn ieithoedd ysgrifenedig yn Nwyrain Asia neu India, gan ddefnyddio bysellfwrdd safonol. Bydd galluogi'r arbrawf hwn yn cadw'r panel bar cyfeiriadau ar agor, dangos canlyniadau chwilio ac awgrymiadau, tra'n defnyddio IME i fewnbynnu testun. Sylwch y gallai'r IME ddangos panel sy'n ymdrin â chanlyniadau'r bar cyfeiriad, felly mae'r dewis hwn yn cael ei awgrymu ar gyfer IME sydd ddim yn defnyddio'r math hwn o banel.
diff --git a/thunderbird-l10n/cy/localization/cy/toolkit/formautofill/formAutofill.ftl b/thunderbird-l10n/cy/localization/cy/toolkit/formautofill/formAutofill.ftl
new file mode 100644
index 0000000000..e197d04005
--- /dev/null
+++ b/thunderbird-l10n/cy/localization/cy/toolkit/formautofill/formAutofill.ftl
@@ -0,0 +1,49 @@
+# This Source Code Form is subject to the terms of the Mozilla Public
+# License, v. 2.0. If a copy of the MPL was not distributed with this
+# file, You can obtain one at http://mozilla.org/MPL/2.0/.
+
+
+## OS Prompt Dialog
+
+# The macos string is preceded by the operating system (macOS) with "Firefox is trying to ",
+# and has a period added to its end. Make sure to test in your locale.
+autofill-use-payment-method-os-prompt-macos = defnyddio manylion cerdyn credyd wedi'i storio
+autofill-use-payment-method-os-prompt-windows = Mae { -brand-short-name } yn ceisio defnyddio manylion dull talu sydd wedi'i storio. Cadarnhewch fynediad i'r cyfrif Windows hwn isod.
+autofill-use-payment-method-os-prompt-other = Mae { -brand-short-name } yn ceisio defnyddio manylion dull talu sydd wedi'i storio.
+# In macOS, this string is preceded by the operating system with "Firefox is trying to ",
+# and has a period added to its end. Make sure to test in your locale.
+autofill-edit-payment-method-os-prompt-macos = dangos manylion dull talu wedi'i storio
+autofill-edit-payment-method-os-prompt-windows = Mae { -brand-short-name } yn ceisio dangos manylion dull talu sydd wedi'i storio. Cadarnhewch fynediad i'r cyfrif Windows hwn isod.
+autofill-edit-payment-method-os-prompt-other = Mae { -brand-short-name } yn ceisio dangos manylion dull talu sydd wedi'i storio.
+# The links lead users to Form Autofill browser preferences.
+autofill-options-link = Dewisiadau Awtolanw Ffurflenni
+autofill-options-link-osx = Dewisiadau Awtolanw Ffurflenni
+
+## The credit card capture doorhanger
+
+# If Sync is enabled and credit card sync is available,
+# this checkbox is displayed on the doorhanger shown when saving credit card.
+credit-card-doorhanger-credit-cards-sync-checkbox = Cydweddu'r holl gardiau sydd wedi'u cadw ar draws fy nyfeisiau
+# Used on the doorhanger when users submit payment with credit card.
+credit-card-save-doorhanger-header = Cadw’r cerdyn hwn yn ddiogel?
+credit-card-save-doorhanger-description = Mae { -brand-short-name } yn amgryptio rhif eich cerdyn. Ni fydd eich cod diogelwch yn cael ei gadw.
+credit-card-capture-save-button =
+    .label = Cadw
+    .accessKey = C
+credit-card-capture-cancel-button =
+    .label = Nid nawr
+    .accessKey = N
+credit-card-capture-never-save-button =
+    .label = Peidio byth a chadw cardiau
+    .accessKey = P
+
+# Used on the doorhanger when an credit card change is detected.
+
+credit-card-update-doorhanger-header = Diweddaru'r cerdyn?
+credit-card-update-doorhanger-description = Cerdyn i'w ddiweddaru:
+credit-card-capture-save-new-button =
+    .label = Cadw fel cerdyn newydd
+    .accessKey = C
+credit-card-capture-update-button =
+    .label = Diweddaru'r cerdyn cyfredol
+    .accessKey = D
diff --git a/thunderbird-l10n/cy/localization/cy/toolkit/global/alert.ftl b/thunderbird-l10n/cy/localization/cy/toolkit/global/alert.ftl
new file mode 100644
index 0000000000..017692ecb6
--- /dev/null
+++ b/thunderbird-l10n/cy/localization/cy/toolkit/global/alert.ftl
@@ -0,0 +1,12 @@
+# This Source Code Form is subject to the terms of the Mozilla Public
+# License, v. 2.0. If a copy of the MPL was not distributed with this
+# file, You can obtain one at http://mozilla.org/MPL/2.0/.
+
+alert-close =
+    .tooltiptext = Cau'r hysbysiad
+alert-settings-title =
+    .tooltiptext = Gosodiadau
+
+## Reminder Notifications
+
+notification-default-dismiss = Cau
diff --git a/thunderbird-l10n/cy/localization/cy/toolkit/global/appPicker.ftl b/thunderbird-l10n/cy/localization/cy/toolkit/global/appPicker.ftl
new file mode 100644
index 0000000000..934d246e63
--- /dev/null
+++ b/thunderbird-l10n/cy/localization/cy/toolkit/global/appPicker.ftl
@@ -0,0 +1,10 @@
+# This Source Code Form is subject to the terms of the Mozilla Public
+# License, v. 2.0. If a copy of the MPL was not distributed with this
+# file, You can obtain one at http://mozilla.org/MPL/2.0/.
+
+app-picker-browse-button =
+    .buttonlabelextra2 = Pori…
+app-picker-send-msg =
+    .value = Anfon yr eitem at:
+app-picker-no-app-found =
+    .value = Heb ganfod rhaglen ar gyfer y math yma o ffeil.
diff --git a/thunderbird-l10n/cy/localization/cy/toolkit/global/browser-utils.ftl b/thunderbird-l10n/cy/localization/cy/toolkit/global/browser-utils.ftl
new file mode 100644
index 0000000000..285aa17ebd
--- /dev/null
+++ b/thunderbird-l10n/cy/localization/cy/toolkit/global/browser-utils.ftl
@@ -0,0 +1,11 @@
+# This Source Code Form is subject to the terms of the Mozilla Public
+# License, v. 2.0. If a copy of the MPL was not distributed with this
+# file, You can obtain one at http://mozilla.org/MPL/2.0/.
+
+# Used for data: URLs where we don't have any useful origin information
+browser-utils-url-data = (data)
+
+# Used for extension URLs
+# Variables:
+#   $extension (string) - Name of the extension that generated the URL
+browser-utils-url-extension = Estyniad ( { $extension } )
diff --git a/thunderbird-l10n/cy/localization/cy/toolkit/global/commonDialog.ftl b/thunderbird-l10n/cy/localization/cy/toolkit/global/commonDialog.ftl
new file mode 100644
index 0000000000..c9fc030fa0
--- /dev/null
+++ b/thunderbird-l10n/cy/localization/cy/toolkit/global/commonDialog.ftl
@@ -0,0 +1,21 @@
+# This Source Code Form is subject to the terms of the Mozilla Public
+# License, v. 2.0. If a copy of the MPL was not distributed with this
+# file, You can obtain one at http://mozilla.org/MPL/2.0/.
+
+common-dialog-title-null = Mae'r dudalen hon yn dweud
+common-dialog-title-system = { -brand-short-name }
+# Title displayed when the origin of a web dialog is unknown.
+common-dialog-title-unknown = Anhysbys
+# An indicator showing that Firefox is waiting for an operation to finish
+common-dialog-spinner =
+    .alt = Prysur
+common-dialog-username =
+    .value = Enw Defnyddiwr
+common-dialog-password =
+    .value = Cyfrinair
+common-dialog-copy-cmd =
+    .label = Copïo
+    .accesskey = C
+common-dialog-select-all-cmd =
+    .label = Dewis Popeth
+    .accesskey = P
diff --git a/thunderbird-l10n/cy/localization/cy/toolkit/global/contextual-identity.ftl b/thunderbird-l10n/cy/localization/cy/toolkit/global/contextual-identity.ftl
new file mode 100644
index 0000000000..9d9e1acbd2
--- /dev/null
+++ b/thunderbird-l10n/cy/localization/cy/toolkit/global/contextual-identity.ftl
@@ -0,0 +1,29 @@
+# This Source Code Form is subject to the terms of the Mozilla Public
+# License, v. 2.0. If a copy of the MPL was not distributed with this
+# file, You can obtain one at http://mozilla.org/MPL/2.0/.
+
+
+## Names of the default containers in Firefox.
+## See https://support.mozilla.org/kb/how-use-firefox-containers
+
+user-context-personal =
+    .label = Personol
+    .accesskey = P
+user-context-work =
+    .label = Gwaith
+    .accesskey = G
+user-context-banking =
+    .label = Bancio
+    .accesskey = B
+user-context-shopping =
+    .label = Siopa
+    .accesskey = S
+
+##
+
+user-context-none =
+    .label = Dim Cynhwysydd
+    .accesskey = D
+user-context-manage-containers =
+    .label = Rheoli Cynwysyddion
+    .accesskey = R
diff --git a/thunderbird-l10n/cy/localization/cy/toolkit/global/cookieBannerHandling.ftl b/thunderbird-l10n/cy/localization/cy/toolkit/global/cookieBannerHandling.ftl
new file mode 100644
index 0000000000..f1860761e3
--- /dev/null
+++ b/thunderbird-l10n/cy/localization/cy/toolkit/global/cookieBannerHandling.ftl
@@ -0,0 +1,5 @@
+# This Source Code Form is subject to the terms of the Mozilla Public
+# License, v. 2.0. If a copy of the MPL was not distributed with this
+# file, You can obtain one at http://mozilla.org/MPL/2.0/.
+
+cookie-banner-handled-webconsole = Mae { -brand-shorter-name } wedi trin baner cwci ar ran y defnyddiwr.
diff --git a/thunderbird-l10n/cy/localization/cy/toolkit/global/createProfileWizard.ftl b/thunderbird-l10n/cy/localization/cy/toolkit/global/createProfileWizard.ftl
new file mode 100644
index 0000000000..01272d092c
--- /dev/null
+++ b/thunderbird-l10n/cy/localization/cy/toolkit/global/createProfileWizard.ftl
@@ -0,0 +1,53 @@
+# This Source Code Form is subject to the terms of the Mozilla Public
+# License, v. 2.0. If a copy of the MPL was not distributed with this
+# file, You can obtain one at http://mozilla.org/MPL/2.0/.
+
+create-profile-window2 =
+    .title = Creu Proffil Dewin
+    .style = min-width: 45em; min-height: 32em;
+
+## First wizard page
+
+create-profile-first-page-header2 =
+    { PLATFORM() ->
+        [macos] Cyflwyniad
+       *[other] Croeso i { create-profile-window2.title }
+    }
+
+profile-creation-explanation-1 = Mae { -brand-short-name } yn storio gwybodaeth am eich gosodiadau a'ch dewisiadau yn eich proffil personol.
+
+profile-creation-explanation-2 = Os ydych yn rhannu'r copi o { -brand-short-name } gyda defnyddwyr eraill, mae modd defnyddio proffiliau i gadw gwybodaeth eich gilydd ar wahân. I wneud hyn, dylai pob defnyddiwr greu ei broffil ei hun.
+
+profile-creation-explanation-3 = Os mai chi yw'r unig berson sy'n defnyddio'r copi o { -brand-short-name }, rhaid i chi gael o leiaf un proffil. Os hoffech chi mae modd creu proffiliau niferus er mwyn cadw gosodiadau a dewisiadau i chi eich hun. Er enghraifft, efallai yr hoffech chi gael proffil gwahanol ar gyfer defnydd busnes neu bersonol.
+
+profile-creation-explanation-4 =
+    { PLATFORM() ->
+        [macos] I gychwyn creu eich proffil, cliciwch Ymlaen.
+       *[other] I gychwyn creu eich proffil, cliciwch Nesaf.
+    }
+
+## Second wizard page
+
+create-profile-last-page-header2 =
+    { PLATFORM() ->
+        [macos] Diweddglo
+       *[other] Cwblhau { create-profile-window2.title }
+    }
+
+profile-creation-intro = Os ydych yn creu nifer o broffiliau mae modd eu gwahaniaethu wrth enw'r proffil. Mae modd defnyddio'r enw sy'n cael ei ddarparu yma neu enw eich hun.
+
+profile-prompt = Rhowch enw proffil newydd:
+    .accesskey = e
+
+profile-default-name =
+    .value = Defnyddiwr Rhagosodedig
+
+profile-directory-explanation = Bydd eich gosodiadau defnyddiwr, dewisiadau a data arall sy'n perthyn i ddefnyddiwr yn cael ei gadw yn:
+
+create-profile-choose-folder =
+    .label = Dewis Ffolder…
+    .accesskey = D
+
+create-profile-use-default =
+    .label = Defnyddio'r Ffolder Rhagosodedig
+    .accesskey = R
diff --git a/thunderbird-l10n/cy/localization/cy/toolkit/global/cspErrors.ftl b/thunderbird-l10n/cy/localization/cy/toolkit/global/cspErrors.ftl
new file mode 100644
index 0000000000..a35dfe828b
--- /dev/null
+++ b/thunderbird-l10n/cy/localization/cy/toolkit/global/cspErrors.ftl
@@ -0,0 +1,32 @@
+# This Source Code Form is subject to the terms of the Mozilla Public
+# License, v. 2.0. If a copy of the MPL was not distributed with this
+# file, You can obtain one at http://mozilla.org/MPL/2.0/.
+
+# Variables:
+#   $directive (String): the name of a CSP directive, such as "script-src".
+csp-error-missing-directive = Nid yw'r polisi'n cynnwys cyfarwyddeb '{ $directive }' angenrheidiol
+
+# Variables:
+#   $directive (String): the name of a CSP directive, such as "script-src".
+#   $keyword (String): the name of a CSP keyword, usually 'unsafe-inline'.
+csp-error-illegal-keyword = Mae '{ $directive }' yn cynnwys cyfarwyddeb gwaharddedig allweddair { $keyword }
+
+# Variables:
+#   $directive (String): the name of a CSP directive, such as "script-src".
+#   $scheme (String): a protocol name, such as "http", which appears as "http:", as it would in a URL.
+csp-error-illegal-protocol = Mae '{ $directive }' yn cynnwys cyfarwyddeb gwaharddedig { $scheme }: protocol ffynhonnell
+
+# Variables:
+#   $directive (String): the name of a CSP directive, such as "script-src".
+#   $scheme (String): a protocol name, such as "http", which appears as "http:", as it would in a URL.
+csp-error-missing-host = { $scheme }: mae'r protocol angen gwestai mewn cyfarwyddeb '{ $directive }'
+
+# Variables:
+#   $directive (String): the name of a CSP directive, such as "script-src".
+#   $source (String): the name of a CSP source, usually 'self'.
+csp-error-missing-source = Rhaid i '{ $directive }' gynnwys y ffynhonnell { $source }
+
+# Variables:
+#   $directive (String): the name of a CSP directive, such as "script-src".
+#   $scheme (String): a protocol name, such as "http", which appears as "http:", as it would in a URL.
+csp-error-illegal-host-wildcard = { $scheme }: rhaid i ffynonellau cerdyn gwyllt o fewn cyfarwyddeb '{ $directive }' gynnwys o leiaf un isbarth generig (e.e., *.example.com yn lle *.com)
diff --git a/thunderbird-l10n/cy/localization/cy/toolkit/global/datepicker.ftl b/thunderbird-l10n/cy/localization/cy/toolkit/global/datepicker.ftl
new file mode 100644
index 0000000000..de426ab708
--- /dev/null
+++ b/thunderbird-l10n/cy/localization/cy/toolkit/global/datepicker.ftl
@@ -0,0 +1,50 @@
+# This Source Code Form is subject to the terms of the Mozilla Public
+# License, v. 2.0. If a copy of the MPL was not distributed with this
+# file, You can obtain one at http://mozilla.org/MPL/2.0/.
+
+
+### Datepicker - Dialog for default HTML's <input type="date">
+
+
+## These labels are used by screenreaders and other assistive technology
+## to indicate the purpose of a date picker calendar and a month-year selection
+## spinner dialogs for HTML's <input type="date">
+
+date-picker-label =
+    .aria-label = Dewiswch ddyddiad
+date-spinner-label =
+    .aria-label = Dewiswch fis a blwyddyn
+
+## Text of the clear button
+
+date-picker-clear-button = Clirio
+
+## These labels are used by screenreaders and other assistive technology
+## to indicate the purpose of buttons that leaf through months of a calendar
+
+date-picker-previous =
+    .aria-label = Mis blaenorol
+date-picker-next =
+    .aria-label = Mis nesaf
+
+## These labels are used by screenreaders and other assistive technology
+## to indicate the type of a value/unit that is being selected within a
+## Month/Year date spinner dialogs on a datepicker calendar dialog
+
+date-spinner-month =
+    .aria-label = Mis
+date-spinner-year =
+    .aria-label = Blwyddyn
+
+## These labels are used by screenreaders and other assistive technology
+## to indicate the purpose of buttons that leaf through either months
+## or years of a Month/Year date spinner on a datepicker calendar dialog
+
+date-spinner-month-previous =
+    .aria-label = Mis blaenorol
+date-spinner-month-next =
+    .aria-label = Mis nesaf
+date-spinner-year-previous =
+    .aria-label = Llynedd
+date-spinner-year-next =
+    .aria-label = Blwyddyn nesaf
diff --git a/thunderbird-l10n/cy/localization/cy/toolkit/global/datetimebox.ftl b/thunderbird-l10n/cy/localization/cy/toolkit/global/datetimebox.ftl
new file mode 100644
index 0000000000..1896c4f656
--- /dev/null
+++ b/thunderbird-l10n/cy/localization/cy/toolkit/global/datetimebox.ftl
@@ -0,0 +1,42 @@
+# This Source Code Form is subject to the terms of the Mozilla Public
+# License, v. 2.0. If a copy of the MPL was not distributed with this
+# file, You can obtain one at http://mozilla.org/MPL/2.0/.
+
+## Placeholders for date and time inputs
+
+datetime-year-placeholder = bbbb
+datetime-month-placeholder = mm
+datetime-day-placeholder = dd
+datetime-time-placeholder = --
+
+## Field labels for input type=date
+
+datetime-year =
+    .aria-label = Blwyddyn
+datetime-month =
+    .aria-label = Mis
+datetime-day =
+    .aria-label = Diwrnod
+
+## Field labels for input type=time
+
+datetime-hour =
+    .aria-label = Awr
+datetime-minute =
+    .aria-label = Munud
+datetime-second =
+    .aria-label = Eiliad
+datetime-millisecond =
+    .aria-label = Milieiliad
+datetime-dayperiod =
+    .aria-label = AM/PM
+
+## Calendar button for input type=date
+
+
+# This label is used by screenreaders and other assistive technology
+# to indicate the purpose of a toggle button inside of the <input type="date">
+# field that opens/closes a date picker calendar dialog
+
+datetime-calendar =
+    .aria-label = Calendr
diff --git a/thunderbird-l10n/cy/localization/cy/toolkit/global/extensionPermissions.ftl b/thunderbird-l10n/cy/localization/cy/toolkit/global/extensionPermissions.ftl
new file mode 100644
index 0000000000..623f86438a
--- /dev/null
+++ b/thunderbird-l10n/cy/localization/cy/toolkit/global/extensionPermissions.ftl
@@ -0,0 +1,33 @@
+# This Source Code Form is subject to the terms of the Mozilla Public
+# License, v. 2.0. If a copy of the MPL was not distributed with this
+# file, You can obtain one at http://mozilla.org/MPL/2.0/.
+
+
+## Extension permission description keys are derived from permission names.
+## Permissions for which the message has been changed and the key updated
+## must have a corresponding entry in the `PERMISSION_L10N_ID_OVERRIDES` map.
+
+webext-perms-description-bookmarks = Darllen a newid nodau tudalen
+webext-perms-description-browserSettings = Darllen a newid gosodiadau'r porwr
+webext-perms-description-browsingData = Clirio'r hanes pori diweddar, cwcis a data cysylltiedig
+webext-perms-description-clipboardRead = Estyn data o'r clipfwrdd
+webext-perms-description-clipboardWrite = Mewnbynnu data i'r clipfwrdd
+webext-perms-description-declarativeNetRequest = Rhwystro cynnwys ar unrhyw dudalen
+webext-perms-description-declarativeNetRequestFeedback = Darllen eich hanes pori
+webext-perms-description-devtools = Estyn offer datblygwyr i gael mynediad at eich data mewn tabiau agored
+webext-perms-description-downloads = Llwytho i lawr, darllen ffeiliau a newid hanes llwytho i lawr y porwr
+webext-perms-description-downloads-open = Agor ffeiliau a llwythwyd i lawr i'ch cyfrifiadur
+webext-perms-description-find = Darllen testun yr holl dabiau sydd ar agor
+webext-perms-description-geolocation = Mynediad i'ch lleoliad
+webext-perms-description-history = Mynediad at eich hanes pori
+webext-perms-description-management = Monitro'r defnydd o estyniadau a rheoli themâu
+webext-perms-description-nativeMessaging = Cyfnewid negeseuon gyda rhaglenni ar wahân i { -brand-short-name }
+webext-perms-description-notifications = Dangos hysbysiadau i chi
+webext-perms-description-pkcs11 = Darparu gwasanaethau dilysiad cryptograffig
+webext-perms-description-privacy = Darllen a newid gosodiadau preifatrwydd
+webext-perms-description-proxy = Rheoli gosodiadau dirprwy'r porwr
+webext-perms-description-sessions = Mynediad at y tabiau caewyd yn ddiweddar
+webext-perms-description-tabs = Mynediad at dabiau'r porwyr
+webext-perms-description-tabHide = Cuddio a dangos tabiau'r porwr
+webext-perms-description-topSites = Mynediad at eich hanes pori
+webext-perms-description-webNavigation = Cael mynediad at weithgaredd wrth lywio
diff --git a/thunderbird-l10n/cy/localization/cy/toolkit/global/extensions.ftl b/thunderbird-l10n/cy/localization/cy/toolkit/global/extensions.ftl
new file mode 100644
index 0000000000..febb321f41
--- /dev/null
+++ b/thunderbird-l10n/cy/localization/cy/toolkit/global/extensions.ftl
@@ -0,0 +1,120 @@
+# This Source Code Form is subject to the terms of the Mozilla Public
+# License, v. 2.0. If a copy of the MPL was not distributed with this
+# file, You can obtain one at http://mozilla.org/MPL/2.0/.
+
+
+## Headers used in the webextension permissions dialog,
+## See https://bug1308309.bmoattachments.org/attachment.cgi?id=8814612
+## for an example of the full dialog.
+## Note: This string will be used as raw markup. Avoid characters like <, >, &
+## Variables:
+##   $extension (String): replaced with the localized name of the extension.
+
+webext-perms-header = Ychwanegu { $extension }?
+webext-perms-header-with-perms = Ychwanegu { $extension }? Bydd gan yr estyniad hwn ganiatâd i:
+webext-perms-header-unsigned = Ychwanegu { $extension }? Nid yw'r estyniad hwn wedi'i wirio. Gall estyniadau maleisus ddwyn eich manylion preifat neu gyfaddawdu eich cyfrifiadur. Ychwanegwch ef dim ond os ydych chi'n ymddiried yn y ffynhonnell.
+webext-perms-header-unsigned-with-perms = Ychwanegu { $extension }? Nid yw'r estyniad hwn wedi'i wirio. Gall estyniadau maleisus ddwyn eich manylion preifat neu gyfaddawdu eich cyfrifiadur. Ychwanegwch ef dim ond os ydych chi'n ymddiried yn y ffynhonnell. Bydd gan yr estyniad hwn ganiatâd i:
+webext-perms-sideload-header = Mae { $extension } wedi ei ychwanegu
+webext-perms-optional-perms-header = Mae { $extension } yn gofyn am ganiatâd ychwanegol.
+
+##
+
+webext-perms-add =
+    .label = Ychwanegu
+    .accesskey = Y
+webext-perms-cancel =
+    .label = Diddymu
+    .accesskey = D
+
+webext-perms-sideload-text = Mae rhaglen arall ar eich cyfrifiadur wedi gosod ychwanegyn y gall effeithio ar eich porwr. Darllenwch geisiadau caniatâd yr ychwanegyn a dewis i Alluogi neu Ddiddymu (ei adael wedi ei analluogi).
+webext-perms-sideload-text-no-perms = Mae rhaglen arall ar eich cyfrifiadur wedi gosod ychwanegyn y gall effeithio ar eich porwr. Darllenwch geisiadau caniatâd yr ychwanegyn a dewis i Alluogi neu Ddiddymu (i'w adael wedi ei analluogi).
+webext-perms-sideload-enable =
+    .label = Galluogi
+    .accesskey = G
+webext-perms-sideload-cancel =
+    .label = Diddymu
+    .accesskey = D
+
+# Variables:
+#   $extension (String): replaced with the localized name of the extension.
+webext-perms-update-text = Mae { $extension } wedi'i ddiweddaru. Rhaid i chi gymeradwyo caniatâd newydd cyn y bydd y fersiwn wedi'i ddiweddaru'n cael ei osod. Bydd dewis “Diddymu” yn cynnal eich fersiwn estyniad cyfredol. Bydd gan yr estyniad hwn ganiatâd i:
+webext-perms-update-accept =
+    .label = Diweddaru
+    .accesskey = D
+
+webext-perms-optional-perms-list-intro = Mae eisiau:
+webext-perms-optional-perms-allow =
+    .label = Caniatáu
+    .accesskey = C
+webext-perms-optional-perms-deny =
+    .label = Gwrthod
+    .accesskey = G
+
+webext-perms-host-description-all-urls = Cael mynediad at eich data ar gyfer pob gwefan
+
+# Variables:
+#   $domain (String): will be replaced by the DNS domain for which a webextension is requesting access (e.g., mozilla.org)
+webext-perms-host-description-wildcard = Cael mynediad at eich data ym mhob gwefan ym mharth { $domain }
+
+# Variables:
+#   $domainCount (Number): Integer indicating the number of additional
+#     hosts for which this webextension is requesting permission.
+webext-perms-host-description-too-many-wildcards =
+    { $domainCount ->
+        [zero] Peidio cael mynediad at eich data mewn parthau eraill
+        [one] Cael mynediad at eich data mewn { $domainCount } parth arall
+        [two] Cael mynediad at eich data mewn { $domainCount } barth arall
+        [few] Cael mynediad at eich data mewn { $domainCount } parth arall
+        [many] Cael mynediad at eich data mewn { $domainCount } parth arall
+       *[other] Cael mynediad at eich data mewn { $domainCount } parth arall
+    }
+# Variables:
+#   $domain (String): will be replaced by the DNS host name for which a webextension is requesting access (e.g., www.mozilla.org)
+webext-perms-host-description-one-site = Cael mynediad at eich data yn { $domain }
+
+# Variables:
+#   $domainCount (Number): Integer indicating the number of additional
+#     hosts for which this webextension is requesting permission.
+webext-perms-host-description-too-many-sites =
+    { $domainCount ->
+        [zero] Peidio cael mynediad at eich data mewn gwefannau eraill
+        [one] Cael mynediad at eich data mewn { $domainCount } gwefan arall
+        [two] Cael mynediad at eich data mewn { $domainCount } wefan arall
+        [few] Cael mynediad at eich data mewn { $domainCount } gwefan arall
+        [many] Cael mynediad at eich data mewn { $domainCount } gwefan arall
+       *[other] Cael mynediad at eich data mewn { $domainCount } gwefan arall
+    }
+
+## Headers used in the webextension permissions dialog for synthetic add-ons.
+## The part of the string describing what privileges the extension gives should be consistent
+## with the value of webext-site-perms-description-gated-perms-{sitePermission}.
+## Note, this string will be used as raw markup. Avoid characters like <, >, &
+## Variables:
+##   $hostname (String): the hostname of the site the add-on is being installed from.
+
+webext-site-perms-header-with-gated-perms-midi = Mae'r ychwanegyn hwn yn rhoi mynediad i { $hostname } i'ch dyfeisiau MIDI.
+webext-site-perms-header-with-gated-perms-midi-sysex = Mae'r ychwanegyn hwn yn rhoi mynediad i { $hostname } i'ch dyfeisiau MIDI (gyda chefnogaeth SysEx).
+
+##
+
+# This string is used as description in the webextension permissions dialog for synthetic add-ons.
+# Note, the empty line is used to create a line break between the two sections.
+# Note, this string will be used as raw markup. Avoid characters like <, >, &
+webext-site-perms-description-gated-perms-midi =
+    Mae'r rhain fel arfer yn ddyfeisiadau plygio i mewn fel syntheseisyddion sain, ond efallai eu bod hefyd wedi'u cynnwys yn eich cyfrifiadur.
+    
+    Nid yw gwefannau yn cael mynediad i ddyfeisiau MIDI fel arfer. Gall ddefnydd amhriodol achosi difrod neu beryglu diogelwch.
+
+## Headers used in the webextension permissions dialog.
+## Note: This string will be used as raw markup. Avoid characters like <, >, &
+## Variables:
+##   $extension (String): replaced with the localized name of the extension being installed.
+##   $hostname (String): will be replaced by the DNS host name for which a webextension enables permissions.
+
+webext-site-perms-header-with-perms = Ychwanegu { $extension }? Mae'r estyniad hwn yn rhoi'r galluoedd canlynol i { $hostname }:
+webext-site-perms-header-unsigned-with-perms = Ychwanegu { $extension }? Nid yw'r estyniad hwn wedi'i wirio. Gall estyniadau maleisus ddwyn eich manylion preifat neu gyfaddawdu eich cyfrifiadur. Ychwanegwch ef dim ond os ydych chi'n ymddiried yn y ffynhonnell. Mae'r estyniad hwn yn rhoi'r galluoedd canlynol i { $hostname }:
+
+## These should remain in sync with permissions.NAME.label in sitePermissions.properties
+
+webext-site-perms-midi = Mynediad at ddyfeisiau MIDI
+webext-site-perms-midi-sysex = Mynediad at ddyfeisiau MIDI sydd â Chefnogaeth SysEx
diff --git a/thunderbird-l10n/cy/localization/cy/toolkit/global/handlerDialog.ftl b/thunderbird-l10n/cy/localization/cy/toolkit/global/handlerDialog.ftl
new file mode 100644
index 0000000000..f20869838c
--- /dev/null
+++ b/thunderbird-l10n/cy/localization/cy/toolkit/global/handlerDialog.ftl
@@ -0,0 +1,70 @@
+# This Source Code Form is subject to the terms of the Mozilla Public
+# License, v. 2.0. If a copy of the MPL was not distributed with this
+# file, You can obtain one at http://mozilla.org/MPL/2.0/.
+
+
+## Permission Dialog
+## Variables:
+##  $host (string) - The hostname that is initiating the request
+##  $scheme (string) - The type of link that's being opened.
+##  $appName (string) - Name of the application that will be opened.
+##  $extension (string) - Name of extension that initiated the request
+
+permission-dialog-description = Caniatáu i'r wefan hon agor y ddolen { $scheme }?
+permission-dialog-description-file = Caniatáu i'r ffeil hon agor y ddolen { $scheme }?
+permission-dialog-description-host = Caniatáu i { $host } agor y ddolen { $scheme }?
+permission-dialog-description-extension = Caniatáu i'r estyniad { $extension } agor y ddolen { $scheme }?
+permission-dialog-description-app = Caniatáu i'r wefan hon agor y ddolen { $scheme } gyda { $appName }?
+permission-dialog-description-host-app = Caniatáu i { $host } agor y ddolen { $scheme } gyda { $appName }?
+permission-dialog-description-file-app = Caniatáu i'r ffeil hon agor y ddolen { $scheme } gyda { $appName }?
+permission-dialog-description-extension-app = Caniatáu i'r estyniad { $extension } agor y ddolen { $scheme } gyda { $appName }?
+permission-dialog-description-system-app = Agor dolen { $scheme } gyda { $appName } ?
+permission-dialog-description-system-noapp = Agor dolen { $scheme }?
+
+## Please keep the emphasis around the hostname and scheme (ie the
+## `<strong>` HTML tags). Please also keep the hostname as close to the start
+## of the sentence as your language's grammar allows.
+## Variables:
+##  $host (string) - The hostname that is initiating the request
+##  $scheme (string) - The type of link that's being opened.
+
+permission-dialog-remember = Caniatáu i <strong>{ $host }</strong> agor dolenni <strong>{ $scheme }</strong> bob tro
+permission-dialog-remember-file = Gadewch i'r ffeil hon agor dolenni <strong>{ $scheme }</strong> bob tro
+permission-dialog-remember-extension = Gadewch i'r estyniad hwn agor dolenni <strong>{ $scheme }</strong> bob tro
+
+##
+
+permission-dialog-btn-open-link =
+    .label = Agor Dolen
+    .accessKey = A
+permission-dialog-btn-choose-app =
+    .label = Dewis Rhaglen
+    .accessKey = R
+permission-dialog-unset-description = Bydd angen i chi ddewis rhaglen.
+permission-dialog-set-change-app-link = Dewiswch raglen arall.
+
+## Chooser dialog
+## Variables:
+##  $scheme (string) - The type of link that's being opened.
+
+chooser-window =
+    .title = Dewis Rhaglen
+    .style = min-width: 26em; min-height: 26em;
+chooser-dialog =
+    .buttonlabelaccept = Agor Dolen
+    .buttonaccesskeyaccept = A
+chooser-dialog-description = Dewiswch raglen i agor y ddolen { $scheme }.
+# Please keep the emphasis around the scheme (ie the `<strong>` HTML tags).
+chooser-dialog-remember = Defnyddiwch y rhaglen hon i agor dolenni <strong>{ $scheme }</strong> bob tro
+chooser-dialog-remember-extra =
+    { PLATFORM() ->
+        [windows] Mae modd newid hwn yn newisiadau { -brand-short-name }.
+       *[other] Mae modd newid hwn yn newisiadau { -brand-short-name }.
+    }
+choose-other-app-description = Dewis Rhaglen arall
+choose-app-btn =
+    .label = Dewis…
+    .accessKey = D
+choose-other-app-window-title = Rhaglen Arall…
+# Displayed under the name of a protocol handler in the Launch Application dialog.
+choose-dialog-privatebrowsing-disabled = Analluogwyd mewn Ffenestri Preifat
diff --git a/thunderbird-l10n/cy/localization/cy/toolkit/global/htmlForm.ftl b/thunderbird-l10n/cy/localization/cy/toolkit/global/htmlForm.ftl
new file mode 100644
index 0000000000..1ad2e47e8c
--- /dev/null
+++ b/thunderbird-l10n/cy/localization/cy/toolkit/global/htmlForm.ftl
@@ -0,0 +1,18 @@
+# This Source Code Form is subject to the terms of the Mozilla Public
+# License, v. 2.0. If a copy of the MPL was not distributed with this
+# file, You can obtain one at http://mozilla.org/MPL/2.0/.
+
+# This string is shown at the end of the tooltip text for
+# <input type='file' multiple> when there are more than 21 files selected
+# (when we will only list the first 20, plus an "and X more" line).
+# Variables:
+#   $fileCount (Number): The number of remaining files.
+input-file-and-more-files =
+    { $fileCount ->
+        [zero] a 0 arall
+        [one] a { $fileCount } arall
+        [two] a { $fileCount } arall
+        [few] a { $fileCount } arall
+        [many] a { $fileCount } arall
+       *[other] a { $fileCount } arall
+    }
diff --git a/thunderbird-l10n/cy/localization/cy/toolkit/global/mozCard.ftl b/thunderbird-l10n/cy/localization/cy/toolkit/global/mozCard.ftl
new file mode 100644
index 0000000000..6fbe8159b2
--- /dev/null
+++ b/thunderbird-l10n/cy/localization/cy/toolkit/global/mozCard.ftl
@@ -0,0 +1,3 @@
+# This Source Code Form is subject to the terms of the Mozilla Public
+# License, v. 2.0. If a copy of the MPL was not distributed with this
+# file, You can obtain one at http://mozilla.org/MPL/2.0/.
diff --git a/thunderbird-l10n/cy/localization/cy/toolkit/global/mozFiveStar.ftl b/thunderbird-l10n/cy/localization/cy/toolkit/global/mozFiveStar.ftl
new file mode 100644
index 0000000000..e350dec840
--- /dev/null
+++ b/thunderbird-l10n/cy/localization/cy/toolkit/global/mozFiveStar.ftl
@@ -0,0 +1,9 @@
+# This Source Code Form is subject to the terms of the Mozilla Public
+# License, v. 2.0. If a copy of the MPL was not distributed with this
+# file, You can obtain one at http://mozilla.org/MPL/2.0/.
+
+# The rating out of 5 stars.
+# Variables:
+#   $rating (number) - A number between 0 and 5. The translation should show at most one digit after the comma.
+moz-five-star-rating =
+    .title = Graddiwyd { NUMBER($rating, maximumFractionDigits: 1) } allan o 5
diff --git a/thunderbird-l10n/cy/localization/cy/toolkit/global/mozMessageBar.ftl b/thunderbird-l10n/cy/localization/cy/toolkit/global/mozMessageBar.ftl
new file mode 100644
index 0000000000..af086338db
--- /dev/null
+++ b/thunderbird-l10n/cy/localization/cy/toolkit/global/mozMessageBar.ftl
@@ -0,0 +1,15 @@
+# This Source Code Form is subject to the terms of the Mozilla Public
+# License, v. 2.0. If a copy of the MPL was not distributed with this
+# file, You can obtain one at http://mozilla.org/MPL/2.0/.
+
+moz-message-bar-icon-info =
+    .alt = Manylion
+moz-message-bar-icon-warning =
+    .alt = Rhybudd
+moz-message-bar-icon-success =
+    .alt = Llwyddiant
+moz-message-bar-icon-error =
+    .alt = Gwall
+moz-message-bar-close-button =
+    .aria-label = Cau
+    .title = Cau
diff --git a/thunderbird-l10n/cy/localization/cy/toolkit/global/mozSupportLink.ftl b/thunderbird-l10n/cy/localization/cy/toolkit/global/mozSupportLink.ftl
new file mode 100644
index 0000000000..8b1b22cd9e
--- /dev/null
+++ b/thunderbird-l10n/cy/localization/cy/toolkit/global/mozSupportLink.ftl
@@ -0,0 +1,5 @@
+# This Source Code Form is subject to the terms of the Mozilla Public
+# License, v. 2.0. If a copy of the MPL was not distributed with this
+# file, You can obtain one at http://mozilla.org/MPL/2.0/.
+
+moz-support-link-text = Darllen rhagor
diff --git a/thunderbird-l10n/cy/localization/cy/toolkit/global/notification.ftl b/thunderbird-l10n/cy/localization/cy/toolkit/global/notification.ftl
new file mode 100644
index 0000000000..899ffcdd7d
--- /dev/null
+++ b/thunderbird-l10n/cy/localization/cy/toolkit/global/notification.ftl
@@ -0,0 +1,14 @@
+# This Source Code Form is subject to the terms of the Mozilla Public
+# License, v. 2.0. If a copy of the MPL was not distributed with this
+# file, You can obtain one at http://mozilla.org/MPL/2.0/.
+
+notification-learnmore-default-label =
+    .value = Darllen rhagor
+# This label is read by screen readers when focusing the close button for an
+# "infobar" (message shown when for example a popup is blocked),
+# and shown when hovering over the button
+notification-close-button =
+    .aria-label = Cau
+    .title = Cau
+close-notification-message =
+    .tooltiptext = Cau'r neges hon
diff --git a/thunderbird-l10n/cy/localization/cy/toolkit/global/popupnotification.ftl b/thunderbird-l10n/cy/localization/cy/toolkit/global/popupnotification.ftl
new file mode 100644
index 0000000000..ea9fa4b506
--- /dev/null
+++ b/thunderbird-l10n/cy/localization/cy/toolkit/global/popupnotification.ftl
@@ -0,0 +1,10 @@
+# This Source Code Form is subject to the terms of the Mozilla Public
+# License, v. 2.0. If a copy of the MPL was not distributed with this
+# file, You can obtain one at http://mozilla.org/MPL/2.0/.
+
+popup-notification-learn-more = Darllen rhagor
+popup-notification-more-actions-button =
+    .aria-label = Rhagor o weithredoedd
+popup-notification-default-button =
+    .label = Iawn!
+    .accesskey = I
diff --git a/thunderbird-l10n/cy/localization/cy/toolkit/global/processTypes.ftl b/thunderbird-l10n/cy/localization/cy/toolkit/global/processTypes.ftl
new file mode 100644
index 0000000000..0ec3eda058
--- /dev/null
+++ b/thunderbird-l10n/cy/localization/cy/toolkit/global/processTypes.ftl
@@ -0,0 +1,61 @@
+# This Source Code Form is subject to the terms of the Mozilla Public
+# License, v. 2.0. If a copy of the MPL was not distributed with this
+# file, You can obtain one at http://mozilla.org/MPL/2.0/.
+
+
+##
+## Localization for remote types defined in RemoteType.h
+##
+
+process-type-web = Cynnwys Gwe
+
+# process used to run privileged about pages,
+# such as about:home
+process-type-privilegedabout = About Breintiedig
+
+# process used to run privileged mozilla pages,
+# such as accounts.firefox.com
+process-type-privilegedmozilla = Cynnwys Mozilla Breintiedig
+
+process-type-extension = Estyniad
+
+# process used to open file:// URLs
+process-type-file = Ffeil Leol
+
+# process used to isolate a webpage from other web pages
+# to improve security
+process-type-webisolated = Cynnwys Gwe Ynysig
+
+# process used to isolate a ServiceWorker to improve
+# performance
+process-type-webserviceworker = Gweithiwr Gwasanaeth Ynysig
+
+# process preallocated; may change to other types
+process-type-prealloc = Rhagddyranwyd
+
+##
+## Localization for Gecko process types defined in GeckoProcessTypes.h
+##
+
+process-type-default = Prif
+process-type-tab = Tab
+
+# process used to communicate with the GPU for
+# graphics acceleration
+process-type-gpu = GPU
+
+# process used to perform network operations
+process-type-socket = Soced
+
+# process used to decode media
+process-type-rdd = RDD
+
+# process used to run some IPC actor in their own sandbox
+process-type-utility = Actor IPC mewn blwch tywod
+
+##
+## Other
+##
+
+# fallback
+process-type-unknown = Anhysbys
diff --git a/thunderbird-l10n/cy/localization/cy/toolkit/global/profileDowngrade.ftl b/thunderbird-l10n/cy/localization/cy/toolkit/global/profileDowngrade.ftl
new file mode 100644
index 0000000000..f66d928d79
--- /dev/null
+++ b/thunderbird-l10n/cy/localization/cy/toolkit/global/profileDowngrade.ftl
@@ -0,0 +1,18 @@
+# This Source Code Form is subject to the terms of the Mozilla Public
+# License, v. 2.0. If a copy of the MPL was not distributed with this
+# file, You can obtain one at http://mozilla.org/MPL/2.0/.
+
+profiledowngrade-window2 =
+    .title = Rydych chi wedi cychwyn fersiwn hŷn o { -brand-product-name }
+    .style = min-width: 490px;
+profiledowngrade-window-create =
+    .label = Creu Proffil Newydd
+profiledowngrade-sync = Mae defnyddio fersiwn hŷn o { -brand-product-name } yn gallu llygru nodau tudalen a hanes pori sydd eisoes wedi'u cadw i broffil { -brand-product-name } cyfredol. Er mwyn diogelu'ch manylion, crëwch broffil newydd ar gyfer gosodiad hwn o { -brand-short-name }. Gallwch fewngofnodi gyda { -fxaccount-brand-name } i gydweddu eich nodau tudalen a'ch hanes pori rhwng proffiliau.
+profiledowngrade-sync2 = Mae defnyddio fersiwn hŷn o { -brand-product-name } yn gallu llygru nodau tudalen a hanes pori sydd eisoes wedi'u cadw i broffil { -brand-product-name } cyfredol. Er mwyn diogelu'ch manylion, crëwch broffil newydd ar gyfer y gosodiad hwn o { -brand-short-name }. Gallwch fewngofnodi gyda chyfrif i gydweddu eich nodau tudalen a'ch hanes pori rhwng proffiliau.
+profiledowngrade-nosync = Mae defnyddio fersiwn hŷn o { -brand-product-name } yn gallu llygru nodau tudalen a hanes pori sydd eisoes wedi'u cadw i broffil { -brand-product-name } presennol. Er mwyn diogelu'ch manylion, crëwch broffil newydd ar gyfer gosod { -brand-short-name }.
+profiledowngrade-quit =
+    .label =
+        { PLATFORM() ->
+            [windows] Gadael
+           *[other] Gadael
+        }
diff --git a/thunderbird-l10n/cy/localization/cy/toolkit/global/profileSelection.ftl b/thunderbird-l10n/cy/localization/cy/toolkit/global/profileSelection.ftl
new file mode 100644
index 0000000000..cf4a22ce0c
--- /dev/null
+++ b/thunderbird-l10n/cy/localization/cy/toolkit/global/profileSelection.ftl
@@ -0,0 +1,38 @@
+# This Source Code Form is subject to the terms of the Mozilla Public
+# License, v. 2.0. If a copy of the MPL was not distributed with this
+# file, You can obtain one at http://mozilla.org/MPL/2.0/.
+
+profile-selection-window =
+    .title = { -brand-short-name } - Dewiswch Broffil Defnyddiwr
+
+profile-selection-button-accept =
+    .label = Cychwyn { -brand-short-name }
+
+profile-selection-button-cancel =
+    .label = Gadael
+
+profile-selection-new-button =
+    .label = Creu Proffil…
+    .accesskey = C
+
+profile-selection-rename-button =
+    .label = Ailenwi Profil…
+    .accesskey = r
+
+profile-selection-delete-button =
+    .label = Dileu Proffil…
+    .accesskey = D
+
+profile-selection-conflict-message = Mae copi arall o { -brand-product-name } wedi gwneud newidiadau i broffiliau. Rhaid ailgychwyn { -brand-short-name } cyn gwneud mwy o newidiadau.
+
+## Messages used in the profile manager
+
+profile-manager-description = Mae { -brand-short-name } yn storio gwybodaeth am eich gosodiadau, dewisiadau ac eitemau defnyddiwr arall yn eich proffil defnyddiwr.
+
+profile-manager-work-offline =
+    .label = Gweithio All-lein
+    .accesskey = o
+
+profile-manager-use-selected =
+    .label = Defnyddio'r proffil penodol heb ofyn wrth gychwyn
+    .accesskey = p
diff --git a/thunderbird-l10n/cy/localization/cy/toolkit/global/resetProfile.ftl b/thunderbird-l10n/cy/localization/cy/toolkit/global/resetProfile.ftl
new file mode 100644
index 0000000000..da584881ed
--- /dev/null
+++ b/thunderbird-l10n/cy/localization/cy/toolkit/global/resetProfile.ftl
@@ -0,0 +1,14 @@
+# This Source Code Form is subject to the terms of the Mozilla Public
+# License, v. 2.0. If a copy of the MPL was not distributed with this
+# file, You can obtain one at http://mozilla.org/MPL/2.0/.
+
+refresh-profile-dialog-title = Adnewyddu { -brand-short-name } i'w osodiadau rhagosodedig?
+refresh-profile-dialog-button =
+    .label = Adnewyddu { -brand-short-name }
+refresh-profile-dialog-description = Ail gychwynnwch o'r newydd i ddatrys problemau perfformiad. Bydd hyn yn dileu eich estyniadau a'ch cyfaddasiadau. Fyddwch chi ddim yn colli gwybodaeth hanfodol fel nodau tudalen a chyfrineiriau.
+refresh-profile = Rhoi bywyd newydd i { -brand-short-name }
+refresh-profile-button = Adnewyddu { -brand-short-name }…
+refresh-profile-learn-more = Darllen rhagor
+refresh-profile-progress =
+    .title = Adnewyddu { -brand-short-name }
+refresh-profile-progress-description = Bron â gorffen…
diff --git a/thunderbird-l10n/cy/localization/cy/toolkit/global/resistFingerPrinting.ftl b/thunderbird-l10n/cy/localization/cy/toolkit/global/resistFingerPrinting.ftl
new file mode 100644
index 0000000000..33e9a7053f
--- /dev/null
+++ b/thunderbird-l10n/cy/localization/cy/toolkit/global/resistFingerPrinting.ftl
@@ -0,0 +1,6 @@
+# This Source Code Form is subject to the terms of the Mozilla Public
+# License, v. 2.0. If a copy of the MPL was not distributed with this
+# file, You can obtain one at http://mozilla.org/MPL/2.0/.
+
+# Spoof Accept-Language prompt
+privacy-spoof-english = O bosib gall newid eich gosodiad i'r iaith Saesneg eich gwneud yn fwy anodd i'ch adnabod a gwella eich preifatrwydd. Hoffech chi wneud cais am fersiynau Saesneg o dudalennau gwe?
diff --git a/thunderbird-l10n/cy/localization/cy/toolkit/global/run-from-dmg.ftl b/thunderbird-l10n/cy/localization/cy/toolkit/global/run-from-dmg.ftl
new file mode 100644
index 0000000000..8b43946363
--- /dev/null
+++ b/thunderbird-l10n/cy/localization/cy/toolkit/global/run-from-dmg.ftl
@@ -0,0 +1,28 @@
+# This Source Code Form is subject to the terms of the Mozilla Public
+# License, v. 2.0. If a copy of the MPL was not distributed with this
+# file, You can obtain one at http://mozilla.org/MPL/2.0/.
+
+
+## Strings for a dialog that may open on macOS before the app's main window
+## opens. The dialog prompts the user to allow the app to install itself in an
+## appropriate location before relaunching itself from that location if the
+## user accepts.
+
+prompt-to-install-title = Gorffen gosod { -brand-short-name }?
+prompt-to-install-message = Cwblhewch y gosodiad un cam hwn i helpu i gadw { -brand-short-name } yn gyfredol a pheidio colli data. Bydd { -brand-short-name } yn cael ei ychwanegu at eich ffolder Rhaglenni a'ch Doc.
+prompt-to-install-yes-button = Gosod
+prompt-to-install-no-button = Peidio â Gosod
+
+## Strings for a dialog that opens if the installation failed.
+
+install-failed-title = Methodd gosod { -brand-short-name }.
+install-failed-message = Methodd { -brand-short-name } â gosod ond bydd yn parhau i redeg.
+
+## Strings for a dialog that recommends to the user to start an existing
+## installation of the app in the Applications directory if one is detected,
+## rather than the app that was double-clicked in a .dmg.
+
+prompt-to-launch-existing-app-title = Agor y rhaglen { -brand-short-name } presennol?
+prompt-to-launch-existing-app-message = Mae { -brand-short-name } eisoes wedi'i osod. Defnyddiwch y rhaglen sydd wedi'i osod i gael y wybodaeth ddiweddaraf ac atal colli data.
+prompt-to-launch-existing-app-yes-button = Agor yr un cyfredol
+prompt-to-launch-existing-app-no-button = Dim diolch
diff --git a/thunderbird-l10n/cy/localization/cy/toolkit/global/tabprompts.ftl b/thunderbird-l10n/cy/localization/cy/toolkit/global/tabprompts.ftl
new file mode 100644
index 0000000000..046d3c5b69
--- /dev/null
+++ b/thunderbird-l10n/cy/localization/cy/toolkit/global/tabprompts.ftl
@@ -0,0 +1,13 @@
+# This Source Code Form is subject to the terms of the Mozilla Public
+# License, v. 2.0. If a copy of the MPL was not distributed with this
+# file, You can obtain one at http://mozilla.org/MPL/2.0/.
+
+tabmodalprompt-username =
+    .value = Enw Defnyddiwr:
+tabmodalprompt-password =
+    .value = Cyfrinair:
+
+tabmodalprompt-ok-button =
+    .label = Iawn
+tabmodalprompt-cancel-button =
+    .label = Diddymu
diff --git a/thunderbird-l10n/cy/localization/cy/toolkit/global/textActions.ftl b/thunderbird-l10n/cy/localization/cy/toolkit/global/textActions.ftl
new file mode 100644
index 0000000000..cd949fd996
--- /dev/null
+++ b/thunderbird-l10n/cy/localization/cy/toolkit/global/textActions.ftl
@@ -0,0 +1,64 @@
+# This Source Code Form is subject to the terms of the Mozilla Public
+# License, v. 2.0. If a copy of the MPL was not distributed with this
+# file, You can obtain one at http://mozilla.org/MPL/2.0/.
+
+text-action-undo =
+    .label = Dadwneud
+    .accesskey = w
+text-action-undo-shortcut =
+    .key = Z
+text-action-redo =
+    .label = Ailwneud
+    .accesskey = A
+text-action-redo-shortcut =
+    .key = Y
+text-action-cut =
+    .label = Torri
+    .accesskey = T
+text-action-cut-shortcut =
+    .key = X
+text-action-copy =
+    .label = Copïo
+    .accesskey = C
+text-action-copy-shortcut =
+    .key = C
+# This command copies the link, removing additional
+# query parameters used to track users across sites.
+text-action-strip-on-share =
+    .label = Copi Heb Tracio Gwefan
+    .accesskey = G
+text-action-paste =
+    .label = Gludo
+    .accesskey = G
+text-action-paste-no-formatting =
+    .label = Gludo heb Fformatio
+    .accesskey = F
+text-action-paste-shortcut =
+    .key = V
+text-action-delete =
+    .label = Dileu
+    .accesskey = i
+text-action-select-all =
+    .label = Dewis Popeth
+    .accesskey = P
+text-action-select-all-shortcut =
+    .key = A
+text-action-spell-no-suggestions =
+    .label = (Dim Awgrymiadau Sillafu)
+text-action-spell-add-to-dictionary =
+    .label = Ychwanegu at y Geiriadur
+    .accesskey = G
+text-action-spell-undo-add-to-dictionary =
+    .label = Dadwneud Ychwanegu at y Geiriadur
+    .accesskey = D
+text-action-spell-check-toggle =
+    .label = Gwirio Sillafu
+    .accesskey = S
+text-action-spell-add-dictionaries =
+    .label = Ychwanegu Geiriaduron…
+    .accesskey = Y
+text-action-spell-dictionaries =
+    .label = Iaith
+    .accesskey = I
+text-action-search-text-box-clear =
+    .title = Clirio
diff --git a/thunderbird-l10n/cy/localization/cy/toolkit/global/timepicker.ftl b/thunderbird-l10n/cy/localization/cy/toolkit/global/timepicker.ftl
new file mode 100644
index 0000000000..6fbe8159b2
--- /dev/null
+++ b/thunderbird-l10n/cy/localization/cy/toolkit/global/timepicker.ftl
@@ -0,0 +1,3 @@
+# This Source Code Form is subject to the terms of the Mozilla Public
+# License, v. 2.0. If a copy of the MPL was not distributed with this
+# file, You can obtain one at http://mozilla.org/MPL/2.0/.
diff --git a/thunderbird-l10n/cy/localization/cy/toolkit/global/tree.ftl b/thunderbird-l10n/cy/localization/cy/toolkit/global/tree.ftl
new file mode 100644
index 0000000000..18aefe0e15
--- /dev/null
+++ b/thunderbird-l10n/cy/localization/cy/toolkit/global/tree.ftl
@@ -0,0 +1,6 @@
+# This Source Code Form is subject to the terms of the Mozilla Public
+# License, v. 2.0. If a copy of the MPL was not distributed with this
+# file, You can obtain one at http://mozilla.org/MPL/2.0/.
+
+tree-columnpicker-restore-order =
+    .label = Adfer Trefn Colofnau
diff --git a/thunderbird-l10n/cy/localization/cy/toolkit/global/unknownContentType.ftl b/thunderbird-l10n/cy/localization/cy/toolkit/global/unknownContentType.ftl
new file mode 100644
index 0000000000..47cb173c7c
--- /dev/null
+++ b/thunderbird-l10n/cy/localization/cy/toolkit/global/unknownContentType.ftl
@@ -0,0 +1,42 @@
+# This Source Code Form is subject to the terms of the Mozilla Public
+# License, v. 2.0. If a copy of the MPL was not distributed with this
+# file, You can obtain one at http://mozilla.org/MPL/2.0/.
+
+unknowncontenttype-handleinternally =
+    .label = Agor gyda { -brand-short-name }
+    .accesskey = A
+
+unknowncontenttype-settingschange =
+    .value =
+        { PLATFORM() ->
+            [windows] Mae modd newid gosodiadau yn Opsiynau { -brand-short-name }.
+           *[other] Mae modd newid gosodiadau yn Dewisiadau { -brand-short-name }.
+        }
+
+unknowncontenttype-intro = Rydych wedi dewis agor:
+unknowncontenttype-which-is = sydd yn:
+unknowncontenttype-from = oddi wrth:
+unknowncontenttype-prompt = Hoffech chi gadw'r ffeil?
+unknowncontenttype-action-question = Beth ddylai { -brand-short-name } wneud gyda'r ffeil?
+unknowncontenttype-open-with =
+    .label = Agor gyda
+    .accesskey = o
+unknowncontenttype-other =
+    .label = Arall…
+unknowncontenttype-choose-handler =
+    .label =
+        { PLATFORM() ->
+            [macos] Dewis…
+           *[other] Pori…
+        }
+    .accesskey =
+        { PLATFORM() ->
+            [macos] D
+           *[other] P
+        }
+unknowncontenttype-save-file =
+    .label = Cadw Ffeil
+    .accesskey = C
+unknowncontenttype-remember-choice =
+    .label = Gwneud hyn yn awtomatig ar gyfer ffeiliau o'r math yma o hyn ymlaen.
+    .accesskey = a
diff --git a/thunderbird-l10n/cy/localization/cy/toolkit/global/videocontrols.ftl b/thunderbird-l10n/cy/localization/cy/toolkit/global/videocontrols.ftl
new file mode 100644
index 0000000000..097778f068
--- /dev/null
+++ b/thunderbird-l10n/cy/localization/cy/toolkit/global/videocontrols.ftl
@@ -0,0 +1,71 @@
+# This Source Code Form is subject to the terms of the Mozilla Public
+# License, v. 2.0. If a copy of the MPL was not distributed with this
+# file, You can obtain one at http://mozilla.org/MPL/2.0/.
+
+# This label is used by screenreaders and other assistive technology to indicate
+# to users how much of the video has been loaded from the network. It will be
+# followed by the percentage of the video that has loaded (e.g. "Loading: 13%").
+videocontrols-buffer-bar-label = Llwytho:
+videocontrols-volume-control =
+    .aria-label = Lefel y sain
+videocontrols-closed-caption-button =
+    .aria-label = Capsiynau Caeedig
+
+videocontrols-play-button =
+    .aria-label = Chwarae
+videocontrols-pause-button =
+    .aria-label = Oedi
+videocontrols-mute-button =
+    .aria-label = Tewi
+videocontrols-unmute-button =
+    .aria-label = Dad dewi
+videocontrols-enterfullscreen-button =
+    .aria-label = Sgrin Lawn
+videocontrols-exitfullscreen-button =
+    .aria-label = Gadael y Sgrin Lawn
+videocontrols-casting-button-label =
+    .aria-label = Darlledu i'r Sgrin
+videocontrols-closed-caption-off =
+    .offlabel = Diffodd
+
+# This string is used as part of the Picture-in-Picture video toggle button when
+# the mouse is hovering it.
+videocontrols-picture-in-picture-label = Llun mewn Llun
+
+# This string is used as the label for a variation of the Picture-in-Picture video
+# toggle button when the mouse is hovering over the video.
+videocontrols-picture-in-picture-toggle-label2 = Agor allan y fideo hwn
+
+videocontrols-picture-in-picture-explainer3 = Mae rhagor o sgriniau'n fwy o hwyl. Chwaraewch y fideo hwn tra byddwch chi'n gwneud pethau eraill.
+
+videocontrols-error-aborted = Mae llwytho'r fideo wedi dod i ben.
+videocontrols-error-network = Mae chwarae'r fideo wedi dod i ben oherwydd gwall rhwydwaith.
+videocontrols-error-decode = Nid oedd modd chwarae'r fideo gan fod y ffeil yn llwgr.
+videocontrols-error-src-not-supported = Nid yw'r fformat fideo na'r math MIME yn cael eu cynnal.
+videocontrols-error-no-source = Heb ganfod fideo gyda fformat sy'n cael ei gynnal na math MIME.
+videocontrols-error-generic = Ataliwyd chwarae'r fideo oherwydd gwall anhysbys.
+videocontrols-status-picture-in-picture = Mae'r fideo hwn yn chwarae yn y modd Llun mewn Llun.
+
+# This message shows the current position and total video duration
+#
+# Variables:
+#   $position (String): The current media position
+#   $duration (String): The total video duration
+#
+# For example, when at the 5 minute mark in a 6 hour long video,
+# $position would be "5:00" and $duration would be "6:00:00", result
+# string would be "5:00 / 6:00:00". Note that $duration is not always
+# available. For example, when at the 5 minute mark in an unknown
+# duration video, $position would be "5:00" and the string which is
+# surrounded by <span> would be deleted, result string would be "5:00".
+videocontrols-position-and-duration-labels = { $position }<span data-l10n-name="position-duration-format"> / { $duration }</span>
+
+# This is a plain text version of the videocontrols-position-and-duration-labels
+# string, used by screenreaders.
+#
+# Variables:
+#   $position (String): The current media position
+#   $duration (String): The total video duration
+videocontrols-scrubber-position-and-duration =
+    .aria-label = Safle
+    .aria-valuetext = { $position } / { $duration }
diff --git a/thunderbird-l10n/cy/localization/cy/toolkit/global/wizard.ftl b/thunderbird-l10n/cy/localization/cy/toolkit/global/wizard.ftl
new file mode 100644
index 0000000000..3f50113b90
--- /dev/null
+++ b/thunderbird-l10n/cy/localization/cy/toolkit/global/wizard.ftl
@@ -0,0 +1,37 @@
+# This Source Code Form is subject to the terms of the Mozilla Public
+# License, v. 2.0. If a copy of the MPL was not distributed with this
+# file, You can obtain one at http://mozilla.org/MPL/2.0/.
+
+wizard-macos-button-back =
+    .label = Mynd Nôl
+    .accesskey = N
+wizard-linux-button-back =
+    .label = Nôl
+    .accesskey = N
+wizard-win-button-back =
+    .label = < Nôl
+    .accesskey = l
+
+wizard-macos-button-next =
+    .label = Ymlaen
+    .accesskey = Y
+wizard-linux-button-next =
+    .label = Nesaf
+    .accesskey = e
+wizard-win-button-next =
+    .label = Nesaf >
+    .accesskey = e
+
+wizard-macos-button-finish =
+    .label = Gorffen
+wizard-linux-button-finish =
+    .label = Gorffen
+wizard-win-button-finish =
+    .label = Gorffen
+
+wizard-macos-button-cancel =
+    .label = Diddymu
+wizard-linux-button-cancel =
+    .label = Diddymu
+wizard-win-button-cancel =
+    .label = Diddymu
diff --git a/thunderbird-l10n/cy/localization/cy/toolkit/intl/languageNames.ftl b/thunderbird-l10n/cy/localization/cy/toolkit/intl/languageNames.ftl
new file mode 100644
index 0000000000..67792fa8b4
--- /dev/null
+++ b/thunderbird-l10n/cy/localization/cy/toolkit/intl/languageNames.ftl
@@ -0,0 +1,215 @@
+# This Source Code Form is subject to the terms of the Mozilla Public
+# License, v. 2.0. If a copy of the MPL was not distributed with this
+# file, You can obtain one at http://mozilla.org/MPL/2.0/.
+
+language-name-aa = Afar
+language-name-ab = Abcasaidd
+language-name-ach = Acholi
+language-name-ae = Avestan
+language-name-af = Affricaneg
+language-name-ak = Akan
+language-name-am = Amhareg
+language-name-an = Aragoneg
+language-name-ar = Arabeg
+language-name-as = Assameje
+language-name-ast = Asturieg
+language-name-av = Avareg
+language-name-ay = Aymara
+language-name-az = Azereg
+language-name-ba = Bashkir
+language-name-be = Belorwseg
+language-name-bg = Bwlgareg
+language-name-bh = Bihari
+language-name-bi = Bislameg
+language-name-bm = Bambara
+language-name-bn = Bengaleg
+language-name-bo = Tibet
+language-name-br = Llydaweg
+language-name-bs = Bosniaeg
+language-name-ca = Catalaneg
+language-name-cak = Kaqchikel
+language-name-ce = Chechen
+language-name-ch = Chamorro
+language-name-co = Corseg
+language-name-cr = Cree
+language-name-crh = Tatar Crimea
+language-name-cs = Tsieceg
+language-name-csb = Kashubian
+language-name-cu = Slafeg Eglwysig
+language-name-cv = Chuvash
+language-name-cy = Cymraeg
+language-name-da = Daeneg
+language-name-de = Almaeneg
+language-name-dsb = Sorbieg Isaf
+language-name-dv = Divehi
+language-name-dz = Dzongkha
+language-name-ee = Ewe
+language-name-el = Groeg
+language-name-en = Saesneg
+language-name-eo = Esperanto
+language-name-es = Sbaeneg
+language-name-et = Estoneg
+language-name-eu = Basgeg
+language-name-fa = Persieg
+language-name-ff = Fulah
+language-name-fi = Ffineg
+language-name-fj = Fijieg
+language-name-fo = Ffaroeg
+language-name-fr = Ffrangeg
+language-name-fur = Ffriulieg
+language-name-fy = Frisieg
+language-name-ga = Gwyddeleg
+language-name-gd = Gaeleg yr Alban
+language-name-gl = Galiseg
+language-name-gn = Gwarani
+language-name-gu = Gwjarati
+language-name-gv = Manaweg
+language-name-ha = Hawsa
+language-name-haw = Hawaieg
+language-name-he = Hebraeg
+language-name-hi = Hindi
+language-name-hil = Hiligaynon
+language-name-ho = Hiri Motu
+language-name-hr = Croateg
+language-name-hsb = Sorbieg Uchaf
+language-name-ht = Haiteg
+language-name-hu = Hwngareg
+language-name-hy = Armeneg
+language-name-hz = Herero
+language-name-ia = Interlingua
+language-name-id = Indonesieg
+language-name-ie = Interlingue
+language-name-ig = Igbo
+language-name-ii = Sichuan Yi
+language-name-ik = Inupiaq
+language-name-io = Ido
+language-name-is = Islandeg
+language-name-it = Eidaleg
+language-name-iu = Inuktitut
+language-name-ja = Siapanaëeg
+language-name-jv = Java
+language-name-ka = Georgeg
+language-name-kab = Kabyle
+language-name-kg = Kongo
+language-name-ki = Kikuyu
+language-name-kj = Kuanyama
+language-name-kk = Kazakh
+language-name-kl = Esgimoeg
+language-name-km = Khmer
+language-name-kn = Kannada
+language-name-ko = Corëeg
+language-name-kok = Konkani
+language-name-kr = Kanuri
+language-name-ks = Kashmir
+language-name-ku = Kwrdeg
+language-name-kv = Komi
+language-name-kw = Cernyweg
+language-name-ky = Kighiz
+language-name-la = Lladin
+language-name-lb = Luxembourgeg
+language-name-lg = Ganda
+language-name-li = Limburgeg
+language-name-lij = Ligurieg
+language-name-ln = Lingala
+language-name-lo = Lao
+language-name-lt = Lithwaneg
+language-name-ltg = Latgalieg
+language-name-lu = Luba-Katanga
+language-name-lv = Latfieg
+language-name-mai = Maithili
+language-name-meh = Tlaxiaco Mixtec y De Orllewin
+language-name-mg = Malagasy
+language-name-mh = Marshalleg
+language-name-mi = Maori
+language-name-mix = Mixtepec Mixtec
+language-name-mk = Macedoneg
+language-name-ml = Malaialam
+language-name-mn = Mongoleg
+language-name-mr = Marathi
+language-name-ms = Malaisieg
+language-name-mt = Malteg
+language-name-my = Byrmaneg
+language-name-na = Nauru
+language-name-nb = Norwyeg Bokmaal
+language-name-nd = Ndebele Gogleddol
+language-name-ne = Nepalieg
+language-name-ng = Ndonga
+language-name-nl = Iseldireg
+language-name-nn = Norwyeg Nynorsk
+language-name-no = Norwyeg
+language-name-nr = Ndebele Deheuol
+language-name-nso = Sotho Gogleddol
+language-name-nv = Navajo
+language-name-ny = Chichewa
+language-name-oc = Occitaneg
+language-name-oj = Ojibwa
+language-name-om = Oromo
+language-name-or = Odia
+language-name-os = Ossetian
+language-name-pa = Punjabeg
+language-name-pi = Pali
+language-name-pl = Pwyleg
+language-name-ps = Pashto
+language-name-pt = Portiwgaleg
+language-name-qu = Quechua
+language-name-rm = Rheto-Romaneg
+language-name-rn = Kirundi
+language-name-ro = Rwmaneg
+language-name-ru = Rwseg
+language-name-rw = Kinyarwanda
+language-name-sa = Sansgrit
+language-name-sat = Santali
+language-name-sc = Sardinieg
+language-name-sco = Scots
+language-name-sd = Sindhi
+language-name-se = Sami Gogleddol
+language-name-sg = Sango
+language-name-si = Sinhala
+language-name-sk = Slofacieg
+language-name-sl = Slofeneg
+language-name-sm = Samoeg
+language-name-sn = Shona
+language-name-so = Somali
+language-name-son = Songhay
+language-name-sq = Albaneg
+language-name-sr = Serbeg
+language-name-ss = Siswati
+language-name-st = Sotho Deheuol
+language-name-su = Sundaneg
+language-name-sv = Swedeg
+language-name-sw = Swahili
+language-name-szl = Silesaidd
+language-name-ta = Tamileg
+language-name-te = Telugu
+language-name-tg = Tajik
+language-name-th = Thai
+language-name-ti = Tigrinya
+language-name-tig = Tigre
+language-name-tk = Turkmen
+language-name-tl = Tagalog
+language-name-tlh = Klingon
+language-name-tn = Tswana
+language-name-to = Tonga
+language-name-tr = Twrceg
+language-name-trs = Triqui
+language-name-ts = Tsonga
+language-name-tt = Tatar
+language-name-tw = Twi
+language-name-ty = Tahiteg
+language-name-ug = Uighur
+language-name-uk = Wcraneg
+language-name-ur = Wrdw
+language-name-uz = Wsbeceg
+language-name-ve = Venda
+language-name-vi = Fietnameg
+language-name-vo = Volapük
+language-name-wa = Walloon
+language-name-wen = Sorbeg
+language-name-wo = Wolof
+language-name-xh = Xhosa
+language-name-yi = Iddeweg
+language-name-yo = Yoruba
+language-name-za = Zhuang
+language-name-zam = Miahuatlán Zapotec
+language-name-zh = Tsieinëeg
+language-name-zu = Zwlweg
diff --git a/thunderbird-l10n/cy/localization/cy/toolkit/intl/regionNames.ftl b/thunderbird-l10n/cy/localization/cy/toolkit/intl/regionNames.ftl
new file mode 100644
index 0000000000..625d71c7d5
--- /dev/null
+++ b/thunderbird-l10n/cy/localization/cy/toolkit/intl/regionNames.ftl
@@ -0,0 +1,280 @@
+# This Source Code Form is subject to the terms of the Mozilla Public
+# License, v. 2.0. If a copy of the MPL was not distributed with this
+# file, You can obtain one at http://mozilla.org/MPL/2.0/.
+
+
+### Notice: If you're updating this list, you should also
+###         update the list in mozIntl.js.
+
+region-name-ad = Andorra
+region-name-ae = United Arab Emirates
+region-name-af = Afghanistan
+region-name-ag = Antigua a Barbuda
+region-name-ai = Anguilla
+region-name-al = Albania
+region-name-am = Armenia
+region-name-ao = Angola
+region-name-aq = Antarctica
+region-name-ar = Ariannin
+region-name-as = Samoa Americanaidd
+region-name-at = Awstria
+region-name-au = Awstralia
+region-name-aw = Aruba
+region-name-az = Azerbaijan
+region-name-ba = Bosnia a Herzegovina
+region-name-bb = Barbados
+region-name-bd = Bangladesh
+region-name-be = Gwlad Belg
+region-name-bf = Burkina Faso
+region-name-bg = Bwlgaria
+region-name-bh = Bahrain
+region-name-bi = Burundi
+region-name-bj = Benin
+region-name-bl = Saint Barthélemy
+region-name-bm = Bermuda
+region-name-bn = Brunei
+region-name-bo = Bolivia
+region-name-bq-2018 = Yr Iseldiroedd Caribïaidd
+region-name-br = Brasil
+region-name-bs = Bahamas
+region-name-bt = Bhutan
+region-name-bv = Ynys Bouvet
+region-name-bw = Botswana
+region-name-by = Belarus
+region-name-bz = Belize
+region-name-ca = Canada
+region-name-cc = Ynysoedd Cocos (Keeling)
+region-name-cd = Congo (Kinshasa)
+region-name-cf = Gweriniaeth Affricanaidd Congo
+region-name-cg = Congo (Brazzaville)
+region-name-ch = Y Swistir
+region-name-ci = Côte d’Ivoire
+region-name-ck = Ynysoedd Cook
+region-name-cl = Chile
+region-name-cm = Cameroon
+region-name-cn = Tsieina
+region-name-co = Colombia
+region-name-cp = Ynys Clipperton
+region-name-cr = Costa Rica
+region-name-cu = Ciwba
+region-name-cv-2020 = Cape Verde
+region-name-cw = Curaçao
+region-name-cx = Ynys Christmas
+region-name-cy = Cyprus
+region-name-cz-2019 = Czechia
+region-name-de = Yr Almaen
+region-name-dg = Diego Garcia
+region-name-dj = Djibouti
+region-name-dk = Denmarc
+region-name-dm = Dominica
+region-name-do = Gweriniaeth Dominica
+region-name-dz = Algeria
+region-name-ec = Ecuador
+region-name-ee = Estonia
+region-name-eg = Yr Aifft
+region-name-eh = Gorllenwin Sahara
+region-name-er = Eritrea
+region-name-es = Sbaen
+region-name-et = Ethiopia
+region-name-fi = Ffindir
+region-name-fj = Ffiji
+region-name-fk = Ynysoedd Malfinas (Falkland)
+region-name-fm = Micronesia, Federated States of
+region-name-fo = Ynysoedd Ffaroe
+region-name-fr = Ffrainc
+region-name-ga = Gabon
+region-name-gb = Y Deyrnas Unedig
+region-name-gd = Grenada
+region-name-ge = Georgia
+region-name-gf = Guiana Ffrengig
+region-name-gg = Guernsey
+region-name-gh = Ghana
+region-name-gi = Gibraltar
+region-name-gl = Greenland
+region-name-gm = Gambia
+region-name-gn = Guinea
+region-name-gp = Guadeloupe
+region-name-gq = Guinea Cyhydeddol
+region-name-gr = Groeg
+region-name-gs = De Georgia ac Ynysoedd De Sandwich
+region-name-gt = Guatemala
+region-name-gu = Guam
+region-name-gw = Guinea-Bissau
+region-name-gy = Guyana
+region-name-hk = Hong Kong
+region-name-hm = Ynys Heard ac Ynys McDonald
+region-name-hn = Honduras
+region-name-hr = Croatia
+region-name-ht = Haiti
+region-name-hu = Hwngari
+region-name-id = Indonesia
+region-name-ie = Iwerddon
+region-name-il = Israel
+region-name-im = Ynys Manaw
+region-name-in = India
+region-name-io = Tiriogaeth Cefnfor Indiaidd Prydain
+region-name-iq = Irac
+region-name-ir = Iran
+region-name-is = Ynys yr Iâ
+region-name-it = Yr Eidal
+region-name-je = Jersey
+region-name-jm = Jamaica
+region-name-jo = Yr Iorddonen
+region-name-jp = Siapan
+region-name-ke = Kenya
+region-name-kg = Kyrgyzstan
+region-name-kh = Cambodia
+region-name-ki = Kiribati
+region-name-km = Comoros
+region-name-kn = Saint Kitts a Nevis
+region-name-kp = Corea, Gogledd
+region-name-kr = Corea, De
+region-name-kw = Kuwait
+region-name-ky = Ynysoedd Cayman
+region-name-kz = Kazakhstan
+region-name-la = Laos
+region-name-lb = Libanus
+region-name-lc = Saint Lucia
+region-name-li = Luxembourg
+region-name-lk = Sri Lanka
+region-name-lr = Liberia
+region-name-ls = Lesotho
+region-name-lt = Lithiwania
+region-name-lu = Liechtenstein
+region-name-lv = Latfia
+region-name-ly = Libya
+region-name-ma = Morocco
+region-name-mc = Monaco
+region-name-md = Moldova
+region-name-me = Montenegro
+region-name-mf = Saint Martin
+region-name-mg = Madagascar
+region-name-mh = Ynysoedd Marshall
+region-name-mk-2019 = Gogledd Macedonia
+region-name-ml = Mali
+region-name-mm = Burma
+region-name-mn = Mongolia
+region-name-mo = Macau
+region-name-mp = Ynysoedd Gogledd Mariana
+region-name-mq = Martinique
+region-name-mr = Mauritania
+region-name-ms = Montserrat
+region-name-mt = Malta
+region-name-mu = Mauritius
+region-name-mv = Maldives
+region-name-mw = Malawi
+region-name-mx = Mecsico
+region-name-my = Malaysia
+region-name-mz = Mozambique
+region-name-na = Namibia
+region-name-nc = Caledonia Newydd
+region-name-ne = Niger
+region-name-nf = Ynys Norfolk
+region-name-ng = Nigeria
+region-name-ni = Nicaragua
+region-name-nl = Yr Iseldiroedd
+region-name-no = Norwy
+region-name-np = Nepal
+region-name-nr = Nauru
+region-name-nu = Niue
+region-name-nz = Seland Newydd
+region-name-om = Oman
+region-name-pa = Panama
+region-name-pe = Periw
+region-name-pf = Polynesia Ffrengig
+region-name-pg = Papua Guinea Newydd
+region-name-ph = Philippines
+region-name-pk = Pacistan
+region-name-pl = Gwlad Pwyl
+region-name-pm = Saint Pierre a Miquelon
+region-name-pn = Ynysoedd Pitcairn
+region-name-pr = Puerto Rico
+region-name-pt = Portiwgal
+region-name-pw = Palau
+region-name-py = Paraguay
+region-name-qa = Qatar
+region-name-qm = Ynysoedd Midway
+region-name-qs = Bassas da India
+region-name-qu = Ynys Juan de Nova
+region-name-qw = Ynys Wake
+region-name-qx = Ynysoedd Glorioso
+region-name-qz = Akrotiri
+region-name-re = Reunion
+region-name-ro = Rwmania
+region-name-rs = Serbia
+region-name-ru = Rwsia
+region-name-rw = Rwanda
+region-name-sa = Saudi Arabia
+region-name-sb = Ynysoedd Solomon
+region-name-sc = Seychelles
+region-name-sd = Swdan
+region-name-se = Sweden
+region-name-sg = Singapore
+region-name-sh = Saint Helena, Ascension, a Tristan da Cunha
+region-name-si = Slofenia
+region-name-sk = Slofacia
+region-name-sl = Sierra Leone
+region-name-sm = San Marino
+region-name-sn = Senegal
+region-name-so = Somalia
+region-name-sr = Suriname
+region-name-ss = De Sudan
+region-name-st = Sao Tome a Principe
+region-name-sv = El Salvador
+region-name-sx = Sint Maarten
+region-name-sy = Syria
+region-name-sz-2019 = Eswatini
+region-name-tc = Ynysoedd Turks a Caicos
+region-name-td = Chad
+region-name-tf = Tiriogaethau De ac Antartic Ffrainc
+region-name-tg = Togo
+region-name-th = Thailand
+region-name-tj = Tajikistan
+region-name-tk = Tokelau
+region-name-tl = Timor-Leste
+region-name-tm = Turkmenistan
+region-name-tn = Tunisia
+region-name-to = Tonga
+region-name-tr = Twrci
+region-name-tt = Trinidad a Tobago
+region-name-tv = Tuvalu
+region-name-tw = Taiwan
+region-name-tz = Tanzania
+region-name-ua = Wcrain
+region-name-ug = Uganda
+region-name-us = Yr Unol Daleithiau
+region-name-uy = Uruguay
+region-name-uz = Uzbekistan
+region-name-va = Dinas y Fatican
+region-name-vc = Saint Vincent a'r Grenadinau
+region-name-ve = Venezuela
+region-name-vg = Ynysoedd Virgin Prydain
+region-name-vi = Ynysoedd Virgin, UDA.
+region-name-vn = Fietnam
+region-name-vu = Vanuatu
+region-name-wf = Wallis a Futuna
+region-name-ws = Samoa
+region-name-xa = Ynysoedd Ashmore a Cartier
+region-name-xb = Ynys Baker
+region-name-xc = Ynysoedd y Môr Cwrel
+region-name-xd = Dhekelia
+region-name-xe = Ynys Europa
+region-name-xg = Llain Gaza
+region-name-xh = Ynys Howland
+region-name-xj = Jan Mayen
+region-name-xk = Kosovo
+region-name-xl = Atol Palmyra
+region-name-xm = Riff Kingman
+region-name-xp = Ynysoedd Parasel
+region-name-xq = Ynys Jarvis
+region-name-xr = Svalbard
+region-name-xs = Ynysoedd Spratly
+region-name-xt = Ynys Tromelin
+region-name-xu = Atol Johnston
+region-name-xv = Ynys Navassa
+region-name-xw = Ardal Gorllewin
+region-name-ye = Yemen
+region-name-yt = Mayotte
+region-name-za = De Affrica
+region-name-zm = Zambia
+region-name-zw = Zimbabwe
diff --git a/thunderbird-l10n/cy/localization/cy/toolkit/main-window/autocomplete.ftl b/thunderbird-l10n/cy/localization/cy/toolkit/main-window/autocomplete.ftl
new file mode 100644
index 0000000000..02fd3c4300
--- /dev/null
+++ b/thunderbird-l10n/cy/localization/cy/toolkit/main-window/autocomplete.ftl
@@ -0,0 +1,24 @@
+# This Source Code Form is subject to the terms of the Mozilla Public
+# License, v. 2.0. If a copy of the MPL was not distributed with this
+# file, You can obtain one at http://mozilla.org/MPL/2.0/.
+
+
+### Import Logins Autocomplete
+
+
+## Variables:
+##   $host (String) - Host name of the current site.
+
+autocomplete-import-logins-chrome =
+    <div data-l10n-name="line1">Mewnforio eich data o o Google Chrome </div>
+    <div data-l10n-name="line2">ar gyfer { $host } a gwefannau eraill</div>
+autocomplete-import-logins-chromium =
+    <div data-l10n-name="line1">Mewnforio eich mewngofnod o Chromium</div>
+    <div data-l10n-name="line2">ar gyfer { $host } a gwefannau eraill</div>
+autocomplete-import-logins-chromium-edge =
+    <div data-l10n-name="line1">Mewnforio eich mewngofnod o Microsoft Edge</div>
+    <div data-l10n-name="line2">ar gyfer { $host } a gwefannau eraill</div>
+
+##
+
+autocomplete-import-learn-more = Darllen rhagor
diff --git a/thunderbird-l10n/cy/localization/cy/toolkit/main-window/findbar.ftl b/thunderbird-l10n/cy/localization/cy/toolkit/main-window/findbar.ftl
new file mode 100644
index 0000000000..ccaeaa5576
--- /dev/null
+++ b/thunderbird-l10n/cy/localization/cy/toolkit/main-window/findbar.ftl
@@ -0,0 +1,84 @@
+# This Source Code Form is subject to the terms of the Mozilla Public
+# License, v. 2.0. If a copy of the MPL was not distributed with this
+# file, You can obtain one at http://mozilla.org/MPL/2.0/.
+
+
+### This file contains the entities needed to use the Find Bar.
+
+findbar-next =
+    .tooltiptext = Canfod enghraifft nesaf yr ymadrodd
+findbar-previous =
+    .tooltiptext = Canfod enghraifft flaenorol o'r ymadrodd
+
+findbar-find-button-close =
+    .tooltiptext = Cau'r bar chwilio
+
+findbar-highlight-all2 =
+    .label = Amlygu Popeth
+    .accesskey =
+        { PLATFORM() ->
+            [macos] l
+           *[other] a
+        }
+    .tooltiptext = Amlygu pob enghraifft o'r ymadrodd
+
+findbar-case-sensitive =
+    .label = Cydweddu Maint
+    .accesskey = C
+    .tooltiptext = Chwilio gyda sensitifrwydd maint nodau
+
+findbar-match-diacritics =
+    .label = Diacritigau Cyfatebol
+    .accesskey = i
+    .tooltiptext = Gwahaniaethu rhwng nodau acennog a nodau sylfaenol, (e.e. wrth chwilio am “resume”, ni fydd “résumé” yn cael ei gynnig)
+
+findbar-entire-word =
+    .label = Geiriau Cyfan
+    .accesskey = G
+    .tooltiptext = Chwilio'r geiriau llawn yn unig
+
+findbar-not-found = Heb ganfod ymadrodd
+
+findbar-wrapped-to-top = Wedi cyrraedd diwedd y dudalen, parhau o'r brig
+findbar-wrapped-to-bottom = Wedi cyrraedd diwedd y dudalen, parhau o'r gwaelod
+
+findbar-normal-find =
+    .placeholder = Canfod ar y dudalen
+findbar-fast-find =
+    .placeholder = Canfod cyflym
+findbar-fast-find-links =
+    .placeholder = Canfod cyflym (dolenni'n unig)
+
+findbar-case-sensitive-status =
+    .value = (Mawr/bach)
+findbar-match-diacritics-status =
+    .value = (Diacritig cyfatebol)
+findbar-entire-word-status =
+    .value = (Geiriau cyfan yn unig)
+
+# Variables:
+#   $current (Number): Index of the currently selected match
+#   $total (Number): Total count of matches
+findbar-found-matches =
+    .value =
+        { $total ->
+            [zero] Dim cydweddiadau
+            [one] { $current } o { $total } cydweddiad
+            [two] { $current } o { $total } gydweddiad
+            [few] { $current } o { $total } cydweddiad
+            [many] { $current } o { $total } chydweddiad
+           *[other] { $current } o { $total } cydweddiad
+        }
+
+# Variables:
+#   $limit (Number): Total count of matches allowed before counting stops
+findbar-found-matches-count-limit =
+    .value =
+        { $limit ->
+            [zero] Dim cydweddiadau
+            [one] Mwy nag { $limit } cydweddiad
+            [two] Mwy na { $limit } gydweddiad
+            [few] Mwy nag { $limit } chydweddiad
+            [many] Mwy nag { $limit } chydweddiad
+           *[other] Mwy nag { $limit } cydweddiad
+        }
diff --git a/thunderbird-l10n/cy/localization/cy/toolkit/neterror/certError.ftl b/thunderbird-l10n/cy/localization/cy/toolkit/neterror/certError.ftl
new file mode 100644
index 0000000000..3331ce408e
--- /dev/null
+++ b/thunderbird-l10n/cy/localization/cy/toolkit/neterror/certError.ftl
@@ -0,0 +1,141 @@
+# This Source Code Form is subject to the terms of the Mozilla Public
+# License, v. 2.0. If a copy of the MPL was not distributed with this
+# file, You can obtain one at http://mozilla.org/MPL/2.0/.
+
+# Variables:
+#   $hostname (string) - Hostname of the website with cert error.
+cert-error-intro = Mae { $hostname } yn defnyddio tystysgrif diogelwch annilys.
+
+cert-error-mitm-intro = Mae gwefannau'n profi eu hunaniaeth drwy dystysgrifau, sy'n cael eu cyhoeddi gan awdurdodau tystysgrifau.
+
+cert-error-mitm-mozilla = Mae { -brand-short-name } yn cael ei gefnogi gan Mozilla y corff dim-er-elw, sy'n gweinyddu storfa awdurdod tystysgrifau (CA) cwbl agored. Mae'r storfa'n cynorthwyo i sicrhau fod awdurdodau tystysgrif yn dilyn ymarfer gorau ar gyfer diogelwch defnyddwyr.
+
+cert-error-mitm-connection = Mae { -brand-short-name } yn defnyddio storfa CA Mozilla i wirio bod cysylltiad yn ddiogel, yn hytrach na thystysgrifau wedi eu cyflenwi gan system weithredu'r defnyddiwr. Felly, os yw rhaglen gwrth-firws neu rwydwaith yn rhyng-gipio cysylltiad â thystysgrif diogelwch a gyhoeddwyd gan CA nad yw yn storfa CA Mozilla, mae'n ystyried bod y cysylltiad yn anniogel.
+
+cert-error-trust-unknown-issuer-intro = Gall fod rhywun yn ceisio efelychu'r wefan a pheidiwch â mynd yn eich blaen.
+
+# Variables:
+#   $hostname (string) - Hostname of the website with cert error.
+cert-error-trust-unknown-issuer = Mae gwefannau'n profi eu hunaniaeth drwy dystysgrifau. Nid yw { -brand-short-name } yn ymddiried yn { $hostname } gan nad yw ei gyhoeddwr tystysgrifau'n hysbys, mae'r dystysgrif wedi ei llofnodi ganddo'i hun neu nid yw'r gweinydd yn anfon y tystysgrifau rhyngol cywir.
+
+cert-error-trust-cert-invalid = Nid oes modd ymddiried yn y dystysgrif am ei fod wedi rhyddhau tystysgrif CA annilys.
+
+cert-error-trust-untrusted-issuer = Nid oes modd ymddiried yn y dystysgrif oherwydd nad oes modd ymddiried yn ei chyhoeddwr.
+
+cert-error-trust-signature-algorithm-disabled = Nid oes ymddiriedaeth i'r dystysgrif gan ei fod wedi ei lofnodi gan ddefnyddio algorithm llofnod sydd wedi ei analluogi am nad yw'r algorithm yn anniogel.
+
+cert-error-trust-expired-issuer = Nid oes modd ymddiried yn y dystysgrif oherwydd bod y dystysgrif ryddhau wedi dod i ben.
+
+cert-error-trust-self-signed = Nid oes modd ymddiried yn y dystysgrif am ei fod wedi ei hunanlofnodi.
+
+cert-error-trust-symantec = Nid yw tystysgrifau a gyhoeddwyd gan GeoTrust, RapidSSL, Symantec, Thawte, a VeriSign bellach yn cael eu hystyried yn ddiogel oherwydd nad oedd yr awdurdodau tystysgrif hyn yn dilyn arferion diogelwch yn y gorffennol.
+
+cert-error-untrusted-default = Nid yw'r dystysgrif yn dod o fan gellir ymddiried ynddo.
+
+# Variables:
+#   $hostname (string) - Hostname of the website with cert error.
+cert-error-domain-mismatch = Mae gwefannau'n profi eu hunaniaeth drwy dystysgrifau. Nid yw { -brand-short-name } yn ymddiried yn y wefan hon gan ei fod yn defnyddio tystysgrif nad yw'n ddilys ar gyfer { $hostname }.
+
+# Variables:
+#   $hostname (string) - Hostname of the website with cert error.
+#   $alt-name (string) - Alternate domain name for which the cert is valid.
+cert-error-domain-mismatch-single = Mae gwefannau'n profi eu hunaniaeth drwy dystysgrifau. Nid yw { -brand-short-name } yn ymddiried yn y wefan hon gan ei fod yn defnyddio tystysgrif nad yw'n ddilys ar gyfer { $hostname }. Dim ond ar gyfer <a data-l10n-name="domain-mismatch-link">{ $alt-name }</a> mae'r dystysgrif yn ddilys.
+
+# Variables:
+#   $hostname (string) - Hostname of the website with cert error.
+#   $alt-name (string) - Alternate domain name for which the cert is valid.
+cert-error-domain-mismatch-single-nolink = Mae gwefannau'n profi eu hunaniaeth drwy dystysgrifau. Nid yw { -brand-short-name } yn ymddiried yn y wefan hon gan ei fod yn defnyddio tystysgrif nad yw'n ddilys ar gyfer { $hostname }. Dim ond ar gyfer { $alt-name } mae'r dystysgrif yn ddilys.
+
+# Variables:
+#   $hostname (string) - Hostname of the website with cert error.
+#   $subject-alt-names (string) - Alternate domain names for which the cert is valid.
+cert-error-domain-mismatch-multiple = Mae gwefannau yn profi eu hunaniaeth trwy dystysgrifau. Nid yw { -brand-short-name } yn ymddiried yn y wefan hon oherwydd ei fod yn defnyddio tystysgrif nad yw'n ddilys ar gyfer { $hostname }. Mae'r dystysgrif yn ddilys yn unig ar gyfer yr enwau canlynol: { $subject-alt-names }
+
+# Variables:
+#   $hostname (string) - Hostname of the website with cert error.
+#   $not-after-local-time (Date) - Certificate is not valid after this time.
+cert-error-expired-now = Mae gwefannau yn profi eu hunaniaeth trwy dystysgrifau, sy'n ddilys am gyfnod penodol. Daeth y dystysgrif ar gyfer { $hostname } i ben ar { $not-after-local-time }.
+
+# Variables:
+#   $hostname (string) - Hostname of the website with cert error.
+#   $not-before-local-time (Date) - Certificate is not valid before this time.
+cert-error-not-yet-valid-now = Mae gwefannau yn profi eu hunaniaeth trwy dystysgrifau, sy'n ddilys am gyfnod penodol. Ni fydd y dystysgrif ar gyfer { $hostname } yn ddilys tan { $not-before-local-time }.
+
+# Variables:
+#   $error (string) - NSS error code string that specifies type of cert error. e.g. unknown issuer, invalid cert, etc.
+cert-error-code-prefix = Cod gwall: { $error }
+
+# Variables:
+#   $error (string) - NSS error code string that specifies type of cert error. e.g. unknown issuer, invalid cert, etc.
+cert-error-code-prefix-link = Cod gwall: <a data-l10n-name="error-code-link">{ $error }</a>
+
+# Variables:
+#   $hostname (string) - Hostname of the website with SSL error.
+#   $errorMessage (string) - Error message corresponding to the type of error we are experiencing.
+cert-error-ssl-connection-error = Digwyddodd gwall wrth gysylltu â { $hostname }. { $errorMessage }
+
+# Variables:
+#   $hostname (string) - Hostname of the website with cert error.
+cert-error-symantec-distrust-description = Mae gwefannau yn profi eu hunaniaeth trwy dystysgrifau, sy'n cael eu cyhoeddir gan awdurdodau tystysgrif. Nid yw'r mwyafrif o borwyr bellach yn ymddiried mewn tystysgrifau a gyhoeddir gan GeoTrust, RapidSSL, Symantec, Thawte, a VeriSign. Mae { $hostname } yn defnyddio tystysgrif gan un o'r awdurdodau hyn ac felly nid oes modd profi hunaniaeth y wefan.
+
+cert-error-symantec-distrust-admin = Gallwch hysbysu gweinyddwr y wefan am y broblem hon.
+
+cert-error-old-tls-version = Mae'n bosibl na fydd y wefan hon yn cefnogi'r protocol TLS 1.2, sef y fersiwn lleiaf a gefnogir gan { -brand-short-name }.
+
+# Variables:
+#   $hasHSTS (Boolean) - Indicates whether HSTS header is present.
+cert-error-details-hsts-label = Diogelwch Trosglwyddo Llym HTTP: { $hasHSTS }
+
+# Variables:
+#   $hasHPKP (Boolean) - Indicates whether HPKP header is present.
+cert-error-details-key-pinning-label = Pinio Allwedd Cyhoeddus HTTP: { $hasHPKP }
+
+cert-error-details-cert-chain-label = Cadwyn tystysgrif:
+
+open-in-new-window-for-csp-or-xfo-error = Agor Gwefan mewn Ffenestr Newydd
+
+# Variables:
+#   $hostname (string) - Hostname of the website blocked by csp or xfo error.
+csp-xfo-blocked-long-desc = Er mwyn amddiffyn eich diogelwch, ni fydd { $hostname } yn caniatáu i { -brand-short-name } ddangos y dudalen os yw gwefan arall wedi'i mewnblannu ynddi. I weld y dudalen hon, bydd angen i chi ei hagor mewn ffenestr newydd.
+
+## Messages used for certificate error titles
+
+connectionFailure-title = Methu cysylltu
+deniedPortAccess-title = Mae'r cyfeiriad wedi ei gyfyngu
+# "Hmm" is a sound made when considering or puzzling over something.
+# You don't have to include it in your translation if your language does not have a written word like this.
+dnsNotFound-title = Hmm. Rydym yn cael trafferth canfod y wefan honno.
+
+dns-not-found-trr-only-title2 = Risg diogelwch posibl wrth chwilio'r parth hwn
+dns-not-found-native-fallback-title2 = Risg diogelwch posibl wrth chwilio'r parth hwn
+
+fileNotFound-title = Heb ganfod ffeil
+fileAccessDenied-title = Mae mynediad at y ffeil wedi ei wrthod
+generic-title = Wps.
+captivePortal-title = Mewngofnodi i'r rhwydwaith
+# "Hmm" is a sound made when considering or puzzling over something.
+# You don't have to include it in your translation if your language does not have a written word like this.
+malformedURI-title = Hmm. Dyw'r cyfeiriad yna ddim yn edrych yn iawn.
+netInterrupt-title = Cafodd y cysylltiad ei darfu
+notCached-title = Daeth y Ddogfen i Ben
+netOffline-title = Modd all-lein
+contentEncodingError-title = Gwall Amgodio Cynnwys
+unsafeContentType-title = Math Anniogel o Ffeil
+netReset-title = Cafodd y cysylltiad ei ailosod
+netTimeout-title = Mae'r cyfnod cyswllt wedi dod i ben
+unknownProtocolFound-title = Heb ddeall y cyfeiriad
+proxyConnectFailure-title = Mae'r gweinydd dirprwy yn gwrthod cysylltiadau
+proxyResolveFailure-title = Methu canfod y gweinydd dirprwyol
+redirectLoop-title = Nid yw'r dudalen yn ailgyfeirio'n iawn
+unknownSocketType-title = Ymateb annisgwyl gan y gweinydd
+nssFailure2-title = Methodd y Cysylltiad Diogel
+csp-xfo-error-title = Nid yw { -brand-short-name } yn Gallu Agor y Dudalen hon
+corruptedContentError-title = Gwall Cynnwys Llygredig
+sslv3Used-title = Methu Cysylltu'n Ddiogel
+inadequateSecurityError-title = Nid yw eich cysylltiad yn ddiogel
+blockedByPolicy-title = Tudalen wedi'i Rhwystro
+clockSkewError-title = Mae cloc eich cyfrifiadur yn anghywir
+networkProtocolError-title = Gwall Protocol Rhwydwaith
+nssBadCert-title = Rhybudd: Risg Diogelwch Posibl o'ch Blaen
+nssBadCert-sts-title = Peidiwch â Chysylltu: Mater Diogelwch Posib
+certerror-mitm-title = Mae Meddalwedd yn Rhwystro { -brand-short-name } Rhag Cysylltu'n Ddiogel i'r Wefan Hon
diff --git a/thunderbird-l10n/cy/localization/cy/toolkit/neterror/netError.ftl b/thunderbird-l10n/cy/localization/cy/toolkit/neterror/netError.ftl
new file mode 100644
index 0000000000..5a7ece3493
--- /dev/null
+++ b/thunderbird-l10n/cy/localization/cy/toolkit/neterror/netError.ftl
@@ -0,0 +1,149 @@
+# This Source Code Form is subject to the terms of the Mozilla Public
+# License, v. 2.0. If a copy of the MPL was not distributed with this
+# file, You can obtain one at http://mozilla.org/MPL/2.0/.
+
+
+## Error page titles
+
+neterror-page-title = Anhawster llwytho tudalen
+certerror-page-title = Rhybudd: Risg Diogelwch Posibl o'ch Blaen
+certerror-sts-page-title = Peidiwch â Chysylltu: Mater Diogelwch Posib
+neterror-blocked-by-policy-page-title = Tudalen wedi'i Rhwystro
+neterror-captive-portal-page-title = Mewngofnodi i'r rhwydwaith
+neterror-dns-not-found-title = Heb Ganfod Gweinydd
+neterror-malformed-uri-page-title = URL annilys
+
+## Error page actions
+
+neterror-advanced-button = Uwch…
+neterror-copy-to-clipboard-button = Copïo testun i'r clipfwrdd
+neterror-learn-more-link = Darllen rhagor…
+neterror-open-portal-login-page-button = Agor Tudalen Mewngofnodi i'r Rhwydwaith
+neterror-override-exception-button = Derbyn y Perygl a Pharhau
+neterror-pref-reset-button = Adfer y gosodiadau rhagosodedig
+neterror-return-to-previous-page-button = Mynd Nôl
+neterror-return-to-previous-page-recommended-button = Ewch Nôl (Argymell)
+neterror-try-again-button = Ceisiwch eto
+neterror-add-exception-button = Parhau bob tro ar gyfer y wefan hon
+neterror-settings-button = Newid gosodiadau DNS
+neterror-view-certificate-link = Darllen Tystysgrif
+neterror-trr-continue-this-time = Parhau'r tro yma
+neterror-disable-native-feedback-warning = Parhau bob tro
+
+##
+
+neterror-pref-reset = Mae'n edrych fel mai eich gosodiadau diogelwch rhwydwaith sy'n achosi hyn. Hoffech chi adfer y gosodiadau rhagosodedig?
+neterror-error-reporting-automatic = Mae adroddiadau gwall fel hyn y cynorthwyo { -vendor-short-name } i adnabod a rhwystro gwefannau maleisus
+
+## Specific error messages
+
+neterror-generic-error = Nid yw { -brand-short-name } yn gallu llwytho'r dudalen am ryw reswm.
+neterror-load-error-try-again = Efallai bod y wefan yn brysur neu nad yw ar gael dros dro. Ceisiwch eto ymhen ychydig.
+neterror-load-error-connection = Os nad ydych yn gallu llwytho unrhyw dudalennau, gwiriwch gysylltiad rhwydwaith eich cyfrifiadur.
+neterror-load-error-firewall = Os yw eich cyfrifiadur neu rwydwaith wedi ei ddiogelu gan fur cadarn neu ddirprwy, gwnewch yn siŵr fod gan { -brand-short-name } hawl i fynediad i'r we.
+neterror-captive-portal = Rhaid i chi fewngofnodi i'r rhwydwaith hwn cyn i chi gael mynediad i'r Rhyngrwyd.
+# Variables:
+# $hostAndPath (String) - a suggested site (e.g. "www.example.com") that the user may have meant instead.
+neterror-dns-not-found-with-suggestion = Oeddech chi'n bwriadu mynd i <a data-l10n-name="website">{ $hostAndPath }</a>?
+neterror-dns-not-found-hint-header = <strong>Os ydych chi wedi rhoi'r cyfeiriad cywir, gallwch:</strong>
+neterror-dns-not-found-hint-try-again = Ceisiwch eto yn nes ymlaen
+neterror-dns-not-found-hint-check-network = Gwiriwch eich cysylltiad rhwydwaith
+neterror-dns-not-found-hint-firewall = Gwiriwch fod gan { -brand-short-name } ganiatâd i gael mynediad i'r we (efallai eich bod wedi'ch cysylltu ond tu ôl i fur cadarn)
+
+## TRR-only specific messages
+## Variables:
+##   $hostname (String) - Hostname of the website to which the user was trying to connect.
+##   $trrDomain (String) - Hostname of the DNS over HTTPS server that is currently in use.
+
+neterror-dns-not-found-trr-only-reason = Nid yw { -brand-short-name } yn gallu diogelu eich cais am gyfeiriad y wefan hon trwy ein datryswr DNS dibynadwy. Dyma pam:
+neterror-dns-not-found-trr-only-reason2 = Nid yw { -brand-short-name } yn gallu diogelu eich cais am gyfeiriad y wefan hon trwy ein datryswr DNS dibynadwy. Dyma pam:
+neterror-dns-not-found-trr-third-party-warning2 = Gallwch barhau â datryswr DNS nad yw'n ddiogel. Fodd bynnag, efallai y bydd trydydd parti yn gallu gweld pa wefannau rydych chi'n ymweld â nhw.
+neterror-dns-not-found-trr-only-could-not-connect = Nid oedd modd i { -brand-short-name } gysylltu â { $trrDomain }.
+neterror-dns-not-found-trr-only-timeout = Cymerodd y cysylltiad i { $trrDomain } fwy o amser na'r disgwyl.
+neterror-dns-not-found-trr-offline = Nid ydych wedi'ch cysylltu â'r rhyngrwyd.
+neterror-dns-not-found-trr-unknown-host2 = Nid yw { $trrDomain } wedi canfod y wefan hon.
+neterror-dns-not-found-trr-server-problem = Bu anhawster gyda { $trrDomain }.
+neterror-dns-not-found-bad-trr-url = URL annilys.
+neterror-dns-not-found-trr-unknown-problem = Anhawster annisgwyl.
+
+## Native fallback specific messages
+## Variables:
+##   $trrDomain (String) - Hostname of the DNS over HTTPS server that is currently in use.
+
+neterror-dns-not-found-native-fallback-reason = Nid yw { -brand-short-name } yn gallu diogelu eich cais am gyfeiriad y wefan hon trwy ein datryswr DNS dibynadwy. Dyma pam:
+neterror-dns-not-found-native-fallback-reason2 = Nid yw { -brand-short-name } yn gallu diogelu eich cais am gyfeiriad y wefan hon trwy ein darparwr DNS dibynadwy. Dyma pam:
+neterror-dns-not-found-native-fallback-heuristic = Mae DNS dros HTTPS wedi'i analluogi ar eich rhwydwaith.
+neterror-dns-not-found-native-fallback-not-confirmed2 = Nid oedd modd i { -brand-short-name } gysylltu â { $trrDomain } .
+
+##
+
+neterror-file-not-found-filename = Gwiriwch yr enw ffeil am brif lythrennu neu wallau teipio eraill.
+neterror-file-not-found-moved = Gwiriwch i weld os yw'r ffeil wedi symud, ailenwi neu ei dileu.
+neterror-access-denied = Gall ei fod wedi ei dynnu, symud neu fod caniatâd ffeiliau yn rhwystro mynediad.
+neterror-unknown-protocol = Efallai bydd angen i chi osod meddalwedd arall i agor y cyfeiriad yma.
+neterror-redirect-loop = Gall y broblem yma fod wedi ei hachosi drwy analluogi neu wrthod cwci.
+neterror-unknown-socket-type-psm-installed = Gwiriwch fod gan eich system Reolwr Diogelwch Personol wedi ei osod.
+neterror-unknown-socket-type-server-config = Gall hyn fod oherwydd ffurfweddiad ansafonol ar y gweinydd.
+neterror-not-cached-intro = Nid yw'r ddogfen gofynnwyd amdani ar gael yn storfa dros dro { -brand-short-name }.
+neterror-not-cached-sensitive = Fel cam i sicrhau diogelwch nid yw { -brand-short-name } yn gofyn eto am ddogfennau sensitif.
+neterror-not-cached-try-again = Cliciwch Ceisio Eto i ofyn eto am y ddogfen o'r wefan.
+neterror-net-offline = Clicio “Ceisio newid eto” i newid i'r modd ar-lein ac ail lwytho'r dudalen.
+neterror-proxy-resolve-failure-settings = Gwiriwch osodiadau'r dirprwy i wneud yn siŵr eu bod yn gywir.
+neterror-proxy-resolve-failure-connection = Gwiriwch fod gan eich cyfrifiadur cyswllt a'r we sy'n gweithio.
+neterror-proxy-resolve-failure-firewall = Os yw eich cyfrifiadur neu rwydwaith wedi ei ddiogelu gan fur cadarn neu ddirprwy, gwnewch yn siŵr fod gan { -brand-short-name } hawl i fynediad i'r we.
+neterror-proxy-connect-failure-settings = Gwiriwch osodiadau'r dirprwy i wneud yn siŵr eu bod yn gywir.
+neterror-proxy-connect-failure-contact-admin = Cysylltwch â'ch gweinyddwr system i wneud yn siŵr fod y gweinydd dirprwyol yn gweithio.
+neterror-content-encoding-error = Cysylltwch â pherchnogion y wefan i'w hysbysu o'r anhawster.
+neterror-unsafe-content-type = Cysylltwch â pherchnogion y wefan i'w hysbysu o'r anhawster.
+neterror-nss-failure-not-verified = Nid oes modd dangos y dudalen rydych yn ceisio ei darllen am nad oes modd dilysu'r data rydych wedi ei dderbyn.
+neterror-nss-failure-contact-website = Cysylltwch â pherchnogion y wefan i'w hysbysu o'r anhawster.
+# Variables:
+# $hostname (String) - Hostname of the website to which the user was trying to connect.
+certerror-intro = Mae { -brand-short-name } wedi canfod bygythiad diogelwch posib ac nid yw wedi mynd i <b>{ $hostname }</b>. Os ewch i'r gwefan yma, gall ymosodwyr geisio dwyn gwybodaeth fel eich cyfrineiriau, e-byst neu fanylion cardiau credyd.
+# Variables:
+# $hostname (String) - Hostname of the website to which the user was trying to connect.
+certerror-sts-intro = Mae { -brand-short-name } wedi canfod bygythiad diogelwch posib ac nid yw wedi mynd i <b>{ $hostname }</b> gan fod y wefan angen cysylltiad diogel.
+# Variables:
+# $hostname (String) - Hostname of the website to which the user was trying to connect.
+certerror-expired-cert-intro = Mae { -brand-short-name } wedi canfod bygythiad diogelwch posib ac nid yw wedi mynd i <b>{ $hostname }</b>. Un ai mae'r wefan wedi ei gam ffurfweddu neu mae cloc eich cyfrifiadur wedi ei osod i'r amser anghywir.
+# Variables:
+# $hostname (String) - Hostname of the website to which the user was trying to connect.
+# $mitm (String) - The name of the software intercepting communications between you and the website (or “man in the middle”)
+certerror-mitm = Mae <b>{ $hostname }</b> mwy na thebyg yn wefan diogel, ond nid oedd modd sefydlu cysylltiad diogel. Achoswyd hyn gan <b>{ $mitm }</b>, sy'n un a'i feddalwedd ar eich cyfrifiadur neu rwydwaith.
+neterror-corrupted-content-intro = Nid oes modd dangos y dudalen rydych yn ceisio ei gweld yn sgil canfod gwall trosglwyddo data.
+neterror-corrupted-content-contact-website = Cysylltwch â pherchnogion y wefan i'w hysbysu o'r anhawster.
+# Do not translate "SSL_ERROR_UNSUPPORTED_VERSION".
+neterror-sslv3-used = Gwybodaeth uwch: SSL_ERROR_UNSUPPORTED_VERSION
+# Variables:
+# $hostname (String) - Hostname of the website to which the user was trying to connect.
+neterror-inadequate-security-intro = <b>{ $hostname }</b> yn defnyddio technoleg diogelwch sy'n hen ac yn agored i ymosodiad. Gall yr ymosodwr weld manylion am hyn roeddech yn meddwl ei fod yn ddiogel. Mae angen i weinyddwr y wefan drwsio'r gweinydd yn gyntaf cyn bod modd i chi ymweld â' r wefan.
+# Do not translate "NS_ERROR_NET_INADEQUATE_SECURITY".
+neterror-inadequate-security-code = Cod gwall: NS_ERROR_NET_INADEQUATE_SECURITY
+# Variables:
+# $hostname (String) - Hostname of the website to which the user was trying to connect.
+# $now (Date) - The current datetime, to be formatted as a date
+neterror-clock-skew-error = Mae eich cyfrifiadur yn meddwl ei bod hi'n { DATETIME($now, dateStyle: "medium") }, sy'n rhwystro { -brand-short-name } rhag cysylltu'n ddiogel. I fynd i <b>{ $hostname }</b>, diweddarwch gloc eich cyfrifiadur yng ngosodiadau eich system i'r dyddiad, amser a chylch amser cyfredol ac yna adnewyddu <b>{ $hostname }</b>.
+neterror-network-protocol-error-intro = Nid oes modd dangos y dudalen rydych yn ceisio'i gweld oherwydd cafwyd gwall yn y protocol rhwydwaith.
+neterror-network-protocol-error-contact-website = Cysylltwch â pherchnogion y wefan i'w hysbysu o'r anhawster.
+certerror-expired-cert-second-para = Mae'n debyg fod tystysgrif y wefan wedi dod i ben, sy'n atal { -brand-short-name } rhag cysylltu'n ddiogell. Os ewch chi i'r wefan hon gall ymosodwyr geisio dwy gwybodaeth fel eich cyfrineiriau, e-byst neu fanylion cerdyn credyd.
+certerror-expired-cert-sts-second-para = Mae'n debyg fod tystysgrif y wefan wedi dod i ben, sy'n atal { -brand-short-name } rhag cysylltu'n ddiogell.
+certerror-what-can-you-do-about-it-title = Beth allwch chi wneud am hyn?
+certerror-unknown-issuer-what-can-you-do-about-it-website = Mae hyn yn fater i'r wefan a does dim fedrwch chi wneud am y peth.
+certerror-unknown-issuer-what-can-you-do-about-it-contact-admin = Os ydych chi ar rwydwaith corfforaethol neu yn defnyddio meddalwedd gwrth-firws gallwch ofyn i'r timau cefnogi am gymorth. Gallwch hefyd hysbysu gweinyddwr y wefan am y broblem.
+# Variables:
+# $hostname (String) - Hostname of the website to which the user was trying to connect.
+# $now (Date) - The current datetime, to be formatted as a date
+certerror-expired-cert-what-can-you-do-about-it-clock = Mae cloc eich cyfrifiadur wedi ei osod i { DATETIME($now, dateStyle: "medium") }. Gwnewch yn siŵr fod y dyddiad, amser a chylch amser yn gywir yn eich gosodiadau system ac yna adnewyddu <b>{ $hostname }</b>.
+certerror-expired-cert-what-can-you-do-about-it-contact-website = Os yw eich cloc eisoes wedi ei osod i'r amser cywir, mwy na thebyg mae'r wefan wedi ei gam osod a does dim fedrwch chi ei wneud i ddatrys y broblem. Gallwch hysbysu gweinyddwr y wefan am y broblem.
+certerror-bad-cert-domain-what-can-you-do-about-it = Mae'n fater i'r wefan a does dim fedrwch chi wneud i ddatrys y mater. Gallwch hysbysu gweinyddwr y wefan am y broblem.
+certerror-mitm-what-can-you-do-about-it-antivirus = Os yw eich meddalwedd gwrth-firws yn cynnwys nodwedd sy'n sganio cysylltiadau wedi eu hamgryptio (“web scanning” neu “https scanning”), gallwch analluogu'r nodwedd honno. Os nad yw hynny'n gweithio, gallwch dynnu ac ailosod y feddalwedd gwrth-firws.
+certerror-mitm-what-can-you-do-about-it-corporate = Os ydych ar rwydwaith corfforaethol, cysylltwch a'ch adran TG.
+# Variables:
+# $mitm (String) - The name of the software intercepting communications between you and the website (or “man in the middle”)
+certerror-mitm-what-can-you-do-about-it-attack = Os nad ydych yn gyfarwydd â <b>{ $mitm }</b>, yna gall hyn fod yn ymosodiad ac ni ddylech barhau ar y wefan hon.
+# Variables:
+# $mitm (String) - The name of the software intercepting communications between you and the website (or “man in the middle”)
+certerror-mitm-what-can-you-do-about-it-attack-sts = Os nad ydych yn gyfarwydd â <b>{ $mitm }</b>, yna gall hyn fod yn ymosodiad ac nid oes dim y gallwch ei wneud i gael mynediad i'r wefan.
+# Variables:
+# $hostname (String) - Hostname of the website to which the user was trying to connect.
+certerror-what-should-i-do-bad-sts-cert-explanation = Mae gan <b>{ $hostname }</b> bolisi diogelwch o'r enw HTTP Strict Transport Security (HSTS), sy'n golygu mai dim ond yn ddiogel mae modd i { -brand-short-name } gysylltu. Nid oes modd gosod eithriad er mwyn ymweld â'r wefan.
diff --git a/thunderbird-l10n/cy/localization/cy/toolkit/neterror/nsserrors.ftl b/thunderbird-l10n/cy/localization/cy/toolkit/neterror/nsserrors.ftl
new file mode 100644
index 0000000000..5602328c2f
--- /dev/null
+++ b/thunderbird-l10n/cy/localization/cy/toolkit/neterror/nsserrors.ftl
@@ -0,0 +1,349 @@
+# This Source Code Form is subject to the terms of the Mozilla Public
+# License, v. 2.0. If a copy of the MPL was not distributed with this
+# file, You can obtain one at http://mozilla.org/MPL/2.0/.
+
+# DO NOT ADD THINGS OTHER THAN ERROR MESSAGES HERE.
+# This file gets parsed into a JS dictionary of all known error message ids in
+# gen_aboutneterror_codes.py . If we end up needing fluent attributes or
+# refactoring them in some way, the script will need updating.
+
+psmerr-ssl-disabled = Methu cysylltu'n ddiogel oherwydd bod y protocol SSL wedi ei analluogi.
+psmerr-ssl2-disabled = Methu cysylltu'n ddiogel oherwydd bod y wefan'n defnyddio hen fersiwn anniogel o brotocol SSL.
+
+# This is a multi-line message.
+psmerr-hostreusedissuerandserial =
+    Rydych wedi derbyn tystysgrif annilys.  Cysylltwch gweinyddwr y gweinydd neu gyfathrebwr e-bost a rhannu'r wybodaeth ganlynol:
+    
+    Mae eich tystysgrif yn cynnwys yr un rhifau cyfresol a thystysgrif arall wedi ei gyhoeddi gan yr awdurdod tystysgrifau.  Defnyddiwch dystysgrif newydd yn cynnwys rhif cyfresol unigryw.
+
+ssl-error-export-only-server = Methu cyfathrebu'n ddiogel. Nid yw'r cyfoed cyn cynnal amgryptiad lefel uchel.
+ssl-error-us-only-server = Methu cyfathrebu'n ddiogel. Mae'r cyfoed angen amgryptiad lefel uchel nad yw'n cael ei gynnal.
+ssl-error-no-cypher-overlap = Methu cyfathrebu'n ddiogel gyda cyfoed: dim algorithm(au) amgrypriad cyffredin.
+ssl-error-no-certificate = Methu canfod tystysgrif neu allwedd angenrheidiol ar gyfer dilysu.
+ssl-error-bad-certificate = Methu cyfathrebu'n ddiogel gyda'r cyfoed: tystysgrif y cyfoed wedi ei wrthod.
+ssl-error-bad-client = Mae'r gweinydd wedi derbyn data gwael gan y cleient.
+ssl-error-bad-server = Mae'r cleient wedi derbyn data gwael gan y gweinydd.
+ssl-error-unsupported-certificate-type = Maeth o dystysgrif sydd heb ei gynnal.
+ssl-error-unsupported-version = Mae'r cyfoed yn defnyddio math o brotocol diogel nad yw'n cael ei gynnal.
+ssl-error-wrong-certificate = Methodd dilysu'r cleient: nid yw allwedd breifat yng nghronfa ddata allweddi yn cydfynd â'r allwedd gyhoeddus yng gntonfa ddata'r tystysgrifau.
+ssl-error-bad-cert-domain = Methu cyfathrebu'n ddiogel gyda'r cyfoed; nid yw'r enw parth yn cydfynd â thystysgrif y gweinydd.
+ssl-error-post-warning = Cod gwall SSL heb ei adnabod.
+ssl-error-ssl2-disabled = Dim ond SSL fersiwn 2 mae'r cyfoed yn ei gynnal ac mae wedi ei analluogi'n lleol.
+ssl-error-bad-mac-read = Derbyniodd SSL gofnod gyda Chod Dilysu Neges anghywir.
+ssl-error-bad-mac-alert = Mae cyfoed SSL yn cofnodi Cod Dilysu Neges anghywir.
+ssl-error-bad-cert-alert = Nid yw cyfode SSL: yn gallu dilysu eich tystysgrif.
+ssl-error-revoked-cert-alert = Mae'r cyfoed SSL wedi gwrthod eich tystysgrif fel un wedi ei atal.
+ssl-error-expired-cert-alert = Mae'r cyfoed SSL wedi gwrthod eich tystysgrif fel un wedi dod i ben.
+ssl-error-ssl-disabled = Methu cysylltu: SSL wedi ei analluogi.
+ssl-error-fortezza-pqg = Methu cysylltu: cyfoed SSL mewn parth FORTEZZA arall.
+ssl-error-unknown-cipher-suite = Mae cais wedi ei dderbyn am swit seiffr SSL.
+ssl-error-no-ciphers-supported = Nid oes swit seiffr ar gael ac wedi eu galluogi yn y rhaglen hon.
+ssl-error-bad-block-padding = Mae SSL wedi derbyn cofnod gyda phadin bloc gwael.
+ssl-error-rx-record-too-long = Mae SSL wedi derbyn cofnod sy'n hirach na'r hyd posib.
+ssl-error-tx-record-too-long = Mae SSL wedi ceisio anfon cofnod sy'n fwy na'r hyd posib.
+ssl-error-rx-malformed-hello-request = Mae SSL wedi derbyn neges ysgwyd llaw Cais Helo anffurf.
+ssl-error-rx-malformed-client-hello = Mae SSL wedi derbyn neges ysgwyd llaw Helo Cleient anffurf.
+ssl-error-rx-malformed-server-hello = Mae SSL wedi derbyn neges ysgwyd llaw Helo Gweinydd anffurf.
+ssl-error-rx-malformed-certificate = Mae SSL wedi derbyn neges ysgwyd llaw Tystysgrif anffurf.
+ssl-error-rx-malformed-server-key-exch = Mae SSL wedi derbyn neges ysgwyd llaw Cyfnewid Allwedd Gweinydd anffurf.
+ssl-error-rx-malformed-cert-request = Derbyniodd SSL neges ysgwyd llaw Cais Tystysgrif anffurfedig.
+ssl-error-rx-malformed-hello-done = Derbyniodd SSL neges ysgwyd llaw Server Hello Done anffurfedig.
+ssl-error-rx-malformed-cert-verify = Mae SSL wedi derbyn neges ysgwyd llaw Dilysu Tystysgrif anffurf.
+ssl-error-rx-malformed-client-key-exch = Mae SSL wedi derbyn neges ysgwyd llaw Cyfnewid Allwedd Cleient anffurf.
+ssl-error-rx-malformed-finished = Mae SSL wedi derbyn neges ysgwyd llaw Terfynnwyd annfurf.
+ssl-error-rx-malformed-change-cipher = Mae SSL wedi derbyn cofnod Manyleb Seiffr Newid anffurf.
+ssl-error-rx-malformed-alert = Mae SSL wedi derbyn cofnod Rhybudd anffurf.
+ssl-error-rx-malformed-handshake = Mae SSL wedi derbyn cofnod Ysgwyd Llaw anffurf.
+ssl-error-rx-malformed-application-data = Mae SSL wedi derbyn cofnod Data Rhaglen Anffurf.
+ssl-error-rx-unexpected-hello-request = Mae SSL wedi derbyn neges ysgwyd llaw Cais Helo annisgwyl.
+ssl-error-rx-unexpected-client-hello = Mae SSL wedi derbyn neges ysgwyd llaw Helo Cleient annisgwyl.
+ssl-error-rx-unexpected-server-hello = Mae SSL wedi derbyn neges ysgwyd llaw Helo Gweinydd annisgwyl.
+ssl-error-rx-unexpected-certificate = Mae SSL wedi derbyn neges ysgwyd llaw Tystysgrif annisgwyl.
+ssl-error-rx-unexpected-server-key-exch = Mae SSL wedi derbyn neges ysgwyd llaw Cyfnewid Allwedd Gweinydd annisgwyl.
+ssl-error-rx-unexpected-cert-request = Mae SSL wedi derbyn neges ysgwyd llaw Cais Tystysgrif annisgwyl.
+ssl-error-rx-unexpected-hello-done = Mae SSL wedi derbyn neges ysgwyd llaw Helo Gweinydd Cwblhawyd annisgwyl.
+ssl-error-rx-unexpected-cert-verify = Mae SSL wedi derbyn neges ysgwyd llaw Dilysu Tystysgrif annisgwyl.
+ssl-error-rx-unexpected-client-key-exch = Mae SSL wedi derbyn neges ysgwyd llaw Cyfnewid Allwedd Cleient annisgwyl.
+ssl-error-rx-unexpected-finished = Mae SSL wedi derbyn neges ysgwyd llaw Terfynnu annisgwyl.
+ssl-error-rx-unexpected-change-cipher = Mae SSL wedi derbyn cofnod Manyleb Seiffr Newid annisgwyl.
+ssl-error-rx-unexpected-alert = Mae SSL wedi derbyn cofnod Rhybudd annisgwyl.
+ssl-error-rx-unexpected-handshake = Mae SSL wedi derbyn cofnod Ysgwyd Llaw annisgwyl.
+ssl-error-rx-unexpected-application-data = Mae SSL wedi derbyn cofnod Data Rhaglen annisgwyl.
+ssl-error-rx-unknown-record-type = Mae SSL wedi derbyn cofnod gyda math data anhysbys.
+ssl-error-rx-unknown-handshake = Mae SSL wedi derbyn negws ysgwyd llaw gyda math data anhysbys.
+ssl-error-rx-unknown-alert = Mae SSL wedi derbyn cofnod rhybudd gyda math disgrifiad anhysbys.
+ssl-error-close-notify-alert = Mae cyfoed SSL wedi cau'r cysylltiad.
+ssl-error-handshake-unexpected-alert = Nid oess y cyfoed SSL yn disgwyl y negws ysgwyd llaw dderbyniodd.
+ssl-error-decompression-failure-alert = Nid oess y cyfoed SSL yn gallu datgywasgu'r cofnod SSL y derbyniodd yn llwyddiannus.
+ssl-error-handshake-failure-alert = Nid oedd cyfoed SSL yn gallu negydu set dderbyniol o baramedrau diogelwch.
+ssl-error-illegal-parameter-alert = Gwrthododd cyfoed SSL neges ysgwyd llaw oherwydd cynnwys annerbyniol.
+ssl-error-unsupported-cert-alert = Nid yw cyfoed SSL yn cynnal tystysgrifau o'r matha mae wedi eu derbyn.
+ssl-error-certificate-unknown-alert = Mae gan gyfoed SSL anhawster amhenodol gyda'r dystysgrif mae wedi ei derbyn.
+ssl-error-generate-random-failure = Profodd SSL fethiant a'o gynhyrchydd rhifau hap.
+ssl-error-sign-hashes-failure = Methu llofnodi data digidol angenrheidiol ar gyfer dilysu eich tystysgrif.
+ssl-error-extract-public-key-failure = Roedd SSL yn methu tynnu'r allwedd gyhoeddus o dystysgrif y cyfoed.
+ssl-error-server-key-exchange-failure = Bu methiant amhenodol wrth brosesu ysgwyd llaw Cyfnewid Allwedd Gweinydd SSL.
+ssl-error-client-key-exchange-failure = Bu methiant amhenodol wrth brosesu ysgwyd llaw Cyfnewid Allwedd Gweinydd SSL.
+ssl-error-encryption-failure = Methodd algorithm amgryptio swmp data yn y swit seiffr hwn.
+ssl-error-decryption-failure = Methodd algorithm dadgryptio swmp data yn y swit seiffr hwn.
+ssl-error-socket-write-failure = Merhodd ymgais i ysgrifennu data amgryptiedig i'r soced gwaelodol.
+ssl-error-md5-digest-failure = Methodd swyddogaeth crynhoi MD5.
+ssl-error-sha-digest-failure = Methodd swyddogaeth crynhoi SHA-1.
+ssl-error-mac-computation-failure = Methodd cyfrifiant MAC.
+ssl-error-sym-key-context-failure = Methu creu cyd-destun Allwedd Symetrig.
+ssl-error-sym-key-unwrap-failure = Methu dadlapio'r allwedd Symetrig yn neges Cyfnewid Allwedd Cleient.
+ssl-error-pub-key-size-limit-exceeded = Ceisiodd Gweinydd SSL â defnyddio allwedd gyhoeddus domestig gyda swit seiffr allforio.
+ssl-error-iv-param-failure = Methodd cod PKCS11 â throsi IV i baram.
+ssl-error-init-cipher-suite-failure = Methu cychwyn y swit seiffr hwn.
+ssl-error-session-key-gen-failure = Methodd y cleient â chynhyrchu allweddi sesiwn ar gyfer sesiwn SSL.
+ssl-error-no-server-key-for-alg = Nid oes gan y gweinydd allwedd ar gyfer ymgais algoryddm cyfnewid allweddi.
+ssl-error-token-insertion-removal = Mewnosodwyd neu dynnwyd tocyn PKCS#11 wrth i'r weithred fod mewn grym.
+ssl-error-token-slot-not-found = Ni fu modd canfod tocyn PKCS#11 i gyflawni'r weithredu.
+ssl-error-no-compression-overlap = Methu cyfathrebu'n ddiogel gyda'r cyfoed: dim algorithmau(au) cywasgu cyffredin.
+ssl-error-handshake-not-completed = Methu cychwyn ysgwyd llaw SSL arall nes i'r ysgwyd llaw cyfredol ddod i ben.
+ssl-error-bad-handshake-hash-value = Wedi derbyn gwerthoedd hash ysgwyd llaw anghywir gan y cyfoed.
+ssl-error-cert-kea-mismatch = Nid oes modd defnyddio'r dystysgrif hon gyda'r algorythm cyfnewid allwedd hwn.
+ssl-error-no-trusted-ssl-client-ca = Nid oes ymddiriedaeth i awdurdod tystysgrifo ar gyfer dilysu cleient SSL.
+ssl-error-session-not-found = Nid yw enw sesiwn SSL y cleient wedi ei ganfod yn storfa dros dro sesiwn y gweinydd.
+ssl-error-decryption-failed-alert = Methodd y cyfoed â dadgryptio cofnod SSL mae wedi ei derbyn.
+ssl-error-record-overflow-alert = Derbyniodd y cyfoed gofnod SSL sy'n hirach na'r hyn ganiateir.
+ssl-error-unknown-ca-alert = Nid yw'r cyfoed yn adnabod nac ymddiried yn y AT sydd wedi cyhoeddi eich tystysgrif.
+ssl-error-access-denied-alert = Derbyniodd y cyfoed dystysgrif dilys , ond gwrthodwyd mynediad.
+ssl-error-decode-error-alert = Nid oedd y cyfoed yn gallu dadgodio neges ysgwyd llaw SSL.
+ssl-error-decrypt-error-alert = Mae'r cyfoed yn cofnodi methiant llofnod dilysu neu gyfnewid allweddi.
+ssl-error-export-restriction-alert = Mae'r cyfoed yn cofnodi negodi nad yw'n gytûn â'r rheoliadau allforio.
+ssl-error-protocol-version-alert = Mae'r cofnod yn cofnodi ferwiwn protocol anghymarus neu heb ei gynnal.
+ssl-error-insufficient-security-alert = Mae'r gweinydd angen seiffr mwy diogel na'r rhai sy'n cael eu cynnal gan y cleient.
+ssl-error-internal-error-alert = Mae'r cyfoed yn nodi gwall mewnol.
+ssl-error-user-canceled-alert = Mae'r cyfoed wedi diddymu ysgwyd llaw.
+ssl-error-no-renegotiation-alert = Nid yw'r cyfoed yn caniatáu ailnegodi paramedrau diogelwch SSL.
+ssl-error-server-cache-not-configured = Nid yw storfa dros dro gweinydd SSL wedi ei ffurfweddu na'i analluogi ar gyfer y soced hwn.
+ssl-error-unsupported-extension-alert = Nid yw'r cyfoed SSL yn cynnal yr estyniad helo TLS gofynnwys amdano.
+ssl-error-certificate-unobtainable-alert = Nid yw'r cyfoed SSL y gallu cael eich tystysgrif o'r URL darparwyd.
+ssl-error-unrecognized-name-alert = Nid oes gan y cyfoed SSL dystysgrif ar gyfer yr enw DNS gofynnwyd amdani.
+ssl-error-bad-cert-status-response-alert = Nid oedd y cyfoed SSL yn gallu cael ymateb OCSP ar gyfer ei dystysgrif.
+ssl-error-bad-cert-hash-value-alert = Adroddodd cyfoed yr SSL gwerth hash tystysgrif gwael.
+ssl-error-rx-unexpected-new-session-ticket = Mae SSL wedi derbyn neges ysgwyd llaw Tocyn Sesiwn Newydd annisgwyl.
+ssl-error-rx-malformed-new-session-ticket = Mae SSL wedi derbyn neges ysgwyd llaw Tocyn Sesiwn Newydd.
+ssl-error-decompression-failure = Mae SSL wedi derbyn cofnod cywasgedig nad oedd modd ei datgywasgu.
+ssl-error-renegotiation-not-allowed = Nid oes modd ail negodi ar y soced SSL hwn.
+ssl-error-unsafe-negotiation = Ceisiodd y cyfoed ysgwyd llaw hen ffurf (bregus posib).
+ssl-error-rx-unexpected-uncompressed-record = Derbyniodd SSL gofnod datgywasgedig annisgwyl.
+ssl-error-weak-server-ephemeral-dh-key = Derbyniodd SSL allwedd gwan Diffie-Hellman darfodedig yn neges ysgwyd llaw Cyfnewidiad Allwedd Gweinydd.
+ssl-error-next-protocol-data-invalid = Derbyniodd SSL ddata estyniad NPN annilys.
+ssl-error-feature-not-supported-for-ssl2 = Nid yw'r nodwedd SSL hwn yn cael ei gynnal ar gyfer cysylltiadau SSL 2.0.
+ssl-error-feature-not-supported-for-servers = Nid yw'r nodweddion SSL hyn yn cael eu cynnal ar weinyddion.
+ssl-error-feature-not-supported-for-clients = Nid yw'r nodweddion SSL hyn yn cael eu cynnal ar raglenni.
+ssl-error-invalid-version-range = Nid ys ystod fersiwn SSL yn ddilys.
+ssl-error-cipher-disallowed-for-version = Dewisodd cyfoed swît seiffr SSL sydd wedi ei atal ar gyfer y protocol fersiwn yma.
+ssl-error-rx-malformed-hello-verify-request = Mae SSL wedi derbyn neges ysgwyd llaw Hello Verify Request anffurf.
+ssl-error-rx-unexpected-hello-verify-request = Mae SSL wedi derbyn neges ysgwyd llaw Hello Verify Request annisgwyl.
+ssl-error-feature-not-supported-for-version = Nid yw'r nodwedd SSL hwn yn cael ei gynnal ar gyfer y fersiwn protocol.
+ssl-error-rx-unexpected-cert-status = Mae SSL wedi derbyn neges ysgwyd llaw Statws Tystysgrif annisgwyl.
+ssl-error-unsupported-hash-algorithm = Algorithm hash anghynaledig wedi ei ddefnyddio gan gyfoed TLS.
+ssl-error-digest-failure = Methodd swyddogaeth crynhoi.
+ssl-error-incorrect-signature-algorithm = Algorithm llofnod anghywir wedi ei bennu mewn elfen llofnod digidol.
+ssl-error-next-protocol-no-callback = Roedd yr estyniad negydu protocol yn barod ond cafodd yr adalw ei glirio cyn fod ei angen.
+ssl-error-next-protocol-no-protocol = Nid yw'r gweinydd yn cynnal protocolau mae'r client yn ei hysbysu yn yr estyniad ALPN.
+ssl-error-inappropriate-fallback-alert = Gwrthododd y gweinydd yr ysgwyd llaw oherwydd i'r client israddio i fersiwn TLS is na mae'r gweinydd yn ei gynnal.
+ssl-error-weak-server-cert-key = Mae tystysgrif y gweinydd yn cynnwys allwedd gyhoeddus sy'n rhy wan.
+ssl-error-rx-short-dtls-read = Dim digon o le ar y byffer ar gyfer cofnod DTLS.
+ssl-error-no-supported-signature-algorithm = Heb ffurfweddu algorithm llofnod TLS sy'n cael ei gynnal.
+ssl-error-unsupported-signature-algorithm = Mae'r cyfoed yn defnyddio cyfuniad o lofnod a'r algorithm hash sydd ddim yn cael ei gynnal.
+ssl-error-missing-extended-master-secret = Mae'r cyfoed wedi ceisio ailgychwyn heb yr estyniad extended_master_secret cywir.
+ssl-error-unexpected-extended-master-secret = Mae'r cyfoed wedi ceisio ailgychwyn gyda estyniad extended_master_secret annisgwyl.
+
+sec-error-io = Digwyddodd gwall I/O yn ystod dilysu diogelwch.
+sec-error-library-failure = methiant llyfrgell diogelwch.
+sec-error-bad-data = llyfrgell diogelwch: derbyniwyd data gwael.
+sec-error-output-len = llyfrgell diogelwch: gwall hyd allbwn.
+sec-error-input-len = mae'r llyfrgell diogelwch wedi profi gwall hyd mewnbwn.
+sec-error-invalid-args = llyfrgell diogewlch: ymrysonderau annilys.
+sec-error-invalid-algorithm = llyfrgell diogewlch: algorithm annilys.
+sec-error-invalid-ava = llyfrgell diogelwch: AVA annilys.
+sec-error-invalid-time = Llinyn amser fformatiwyd yn annilys.
+sec-error-bad-der = llyfrgell diogelwch: neges amgodiad-DER wedi ei fformatio'n annilys.
+sec-error-bad-signature = Mae gan y tystysgrif cyfoed lofnod annilys.
+sec-error-expired-certificate = Tystysgrif Cyfoed wedi dod i ben.
+sec-error-revoked-certificate = Tystysgrif Cyfoed wedi ei atal.
+sec-error-unknown-issuer = Cyhoeddwr Tystysgrif Cyfoed heb ei adnabod.
+sec-error-bad-key = Allwedd cyhoeddus y cyfoed yn annilys.
+sec-error-bad-password = Mae'r cyfrinair diogelwch yn anghywir.
+sec-error-retry-password = Cyfrinair newydd yn anghywir. Ceisiwch eto.
+sec-error-no-nodelock = llyfrgell diogelwch: dim clo nod.
+sec-error-bad-database = llyfrgell diogewlch: cronfa ddata gwael.
+sec-error-no-memory = llyfrgell diogewlch: methiant dynodicof.
+sec-error-untrusted-issuer = Cyhoeddwr tystysgrif cyfoed wedi ei nodi fel annibynadwy gan y defnyddiwr.
+sec-error-untrusted-cert = Tstysgrif cyfoed wedi ei nodi fel annibynadwy gan y defnyddiwr.
+sec-error-duplicate-cert = Mae'r tystysgrif yn bodoli yn eich cronfa ddata.
+sec-error-duplicate-cert-name = Mae enw'r dystysgrif llwythwyd i lawr yn dyblygu un sydd yn eich cronfa ddata.
+sec-error-adding-cert = Gwall ychwanegu tystysgrif i'r gronfa ddata.
+sec-error-filing-key = Gwall ail-lanw allwedd ar gyfer y dystysgrif.
+sec-error-no-key = Nid oes modd dod o hyd i allwedd breifat y dystysgrif yng gronfa ddata allweddi
+sec-error-cert-valid = Mae'r dystysgrif yn ddilys.
+sec-error-cert-not-valid = Nid yw'r dystysgrif yn ddilys.
+sec-error-cert-no-response = Llyfrgell Tyst: Dim Ymateb
+sec-error-expired-issuer-certificate = Ma tystysgrif cyhoeddwr y dystysgrif wedi dod i ben. Gwiriwch ddyddiad ac amser eich system.
+sec-error-crl-expired = Mae CRL cyhoeddwr y dystysgrif wedi dod i ben. Diweddarwch neu gwiriwch ddyddiad ac amser eich system.
+sec-error-crl-bad-signature = Mae i CRL cyhoeddwr y dystysgrif lofnod annilys.
+sec-error-crl-invalid = Mae i'r CRL newydd fformat annilys.
+sec-error-extension-value-invalid = Mae gwerth estyniad tystysgrif yn annilys.
+sec-error-extension-not-found = Heb ganfod estyniad tystysgrif.
+sec-error-ca-cert-invalid = Tystysgrif y cyhoeddwr yn annilys.
+sec-error-path-len-constraint-invalid = Mae cyfyniad hyd llwybr y dystysgrif yn annilys.
+sec-error-cert-usages-invalid = Mae maes defnydd tystysgrif yn annilys.
+sec-internal-only = **Modiwl Mewnol YN UNIG**
+sec-error-invalid-key = Nid yw'r allwedd yn cynnal y weithred hon.
+sec-error-unknown-critical-extension = Mae'r dystysgrif yn cynnwys estyniad critigol anhysbys.
+sec-error-old-crl = Nid yw'r CRL yn hwyrach na'r un gyfredol.
+sec-error-no-email-cert = Heb ei hamgryptio na'i harwyddo: nid oes gennych dystysgrif e-bost eto.
+sec-error-no-recipient-certs-query = Heb ei hamgryptio: nid oes gennych dystysgrif ar gyfer pob un derbynnydd.
+sec-error-not-a-recipient = Methu dadgryptio: nid ydych yn dderbynnydd, neu heb ganfod tystysgrif cytûn neu allwedd breifat.
+sec-error-pkcs7-keyalg-mismatch = Methu dadgryptio: nid yw amgryptiad yr algorithm yn gytûn â'ch tystysgrif.
+sec-error-pkcs7-bad-signature = Methodd dilysu llofnod: heb ganfod llofnodwr, wedi canfod gormod o lofnodwyr neu data amhriodol neu llwgr.
+sec-error-unsupported-keyalg = Allwedd algorithm heb ei gynnal neu anhysbys.
+sec-error-decryption-disallowed = Methu dadgryptio: wedi ei amgryptio gan ddefnyddio algorithm gwaharddedig neu faint allwedd.
+sec-error-no-krl = Heb ganfod KRL ar gyfer tystysgrif y wefan.
+sec-error-krl-expired = Mae KRL y wefan wedi dod i ben.
+sec-error-krl-bad-signature = Mae llofnod annilys i KRL tystysgrif y wefan.
+sec-error-revoked-key = Mae allwedd tystysgrif y wefan honn wedi ei therfynnu.
+sec-error-krl-invalid = Mae fformat annilys i'r KRL newydd.
+sec-error-need-random = llyfrgell diogelwch: angen data hap.
+sec-error-no-module = llyfrgell diogelwch: nid oes modiwl diogelwch all gyflawni'r weithred angenrheidiol.
+sec-error-no-token = Nid yw'r cerdyn neu docyn diogelwch yn bodoli, angen ei gychwyn neu wedi ei dynnu.
+sec-error-read-only = llyfrgell diogelwch: cronfa ddata darllen yn unig.
+sec-error-no-slot-selected = Heb ddewis slot neu docyn.
+sec-error-cert-nickname-collision = Mae tystysgrif gyda'r un llysenw yn bodoli eisoes.
+sec-error-key-nickname-collision = Mae allwedd gyda'r un llysenw yn bodoli eisoes.
+sec-error-safe-not-created = gwall wrth greu gwrthrych diogel
+sec-error-baggage-not-created = gwall werth greu gwrthrych pecyn
+sec-error-bad-export-algorithm = Nid oes caniatâd i'r algorithm angenrheidiol.
+sec-error-exporting-certificates = Gwall wrth geisio allforio tystysgrifau.
+sec-error-importing-certificates = Gwall wrth geisio mewnforio tystysgrifau.
+sec-error-pkcs12-decoding-pfx = Methu mewnforio. Gwall dadgodio. Nid yw'r ffeil yn ddilys.
+sec-error-pkcs12-invalid-mac = Methu mewnforio. MAC annilys. Cyfrinair anghywir neu ffeil llwgr.
+sec-error-pkcs12-unsupported-mac-algorithm = Methu mewnforio. Nid yw'r algorithm MAC yn cael ei gynnal.
+sec-error-pkcs12-unsupported-transport-mode = Methu mewnforio. Dim ond cywirdeb cyfrinair a moddau preifatrwydd sy'n cael eu cynnal.
+sec-error-pkcs12-corrupt-pfx-structure = Methu mewnforio. Mae strwythur y ffeil yn llwgr.
+sec-error-pkcs12-unsupported-pbe-algorithm = Methu mewnforio. Nid yw algorithm yr amgryptio'n cael ei gynnal.
+sec-error-pkcs12-unsupported-version = Methu mewnforio. Nid yw fersiwn y ffeil yn cael ei chynnal.
+sec-error-pkcs12-privacy-password-incorrect = Methu mewnforio. Cyfrinair preifatrwydd anghywir.
+sec-error-pkcs12-cert-collision = Methu mewnforio. Mae'r un llysenw yn bodoli eisoes yn y gronfa ddata.
+sec-error-user-cancelled = Pwysodd y defnyddiwr diddymu.
+sec-error-pkcs12-duplicate-data = Heb ei fewnforio, eisoes yn y gronfa ddata.
+sec-error-message-send-aborted = Heb anfon y neges.
+sec-error-inadequate-key-usage = Defnydd allwedd y dystysgrif yn annigonol ar gyfer y weithred ymgeisiwyd.
+sec-error-inadequate-cert-type = Nid yw'r math o dystysgrif wedi ei gymeradwyo ar gyfer y rhaglen.
+sec-error-cert-addr-mismatch = Nid yw'r cyfeiriad yn y dysstysgrif llofnodi yn cydfynd â'r cyferiad ym mhenyn y neges.
+sec-error-pkcs12-unable-to-import-key = Methu mewnforio. Gwall wrth geisio mewnforio'r allwedd breifat.
+sec-error-pkcs12-importing-cert-chain = Methu mewnforio. Gwall wrth geisio mewnforio cadwyn tystysgrif.
+sec-error-pkcs12-unable-to-locate-object-by-name = Methu allforio. Methu lleoli tystysgrif neu allwedd yn ôl tystysgrif.
+sec-error-pkcs12-unable-to-export-key = Methu allforio. Nid oedd modd canfod yr Allwedd Breifat a'i hallforio.
+sec-error-pkcs12-unable-to-write = Methu allforio. Methu ysgrifennu i'r ffeil allforio.
+sec-error-pkcs12-unable-to-read = Methu mewnforio. Methu darllen y ffeil mewnforio.
+sec-error-pkcs12-key-database-not-initialized = Methu allforio. Cronfa ddata'r allwedd yn llwgr neu wedi ei dileu.
+sec-error-keygen-fail = Methu cynhyrchu par o allweddi cyhoeddus/preifat.
+sec-error-invalid-password = Mae'r cyfrinair rhoddwyd yn annilys. Dewiswch un arall.
+sec-error-retry-old-password = Mae'r hen gyfrinair wedi ei gosod yn anghywir. Ceisiwch eto.
+sec-error-bad-nickname = Mae llysenw'r dystysgrif yn cael ei defnyddio eisoes.
+sec-error-not-fortezza-issuer = Mae gan y cadwyn FORTEZZA cyfoed dystysgrif an FORTEZZA.
+sec-error-cannot-move-sensitive-key = Nid oes modd symud allwedd sensitif i'r slot lle mae ei hangen.
+sec-error-js-invalid-module-name = Enw modiwl annilys.
+sec-error-js-invalid-dll = Llwybr/enw ffeil modiwl annilys
+sec-error-js-add-mod-failure = Methu ychwanegu modiwl
+sec-error-js-del-mod-failure = Methu dileu modiwl
+sec-error-old-krl = Nid yw'r KRL newydd yn hwyrach na'r un cyfredol.
+sec-error-ckl-conflict = Mae gan y CKL gyhoeddwr gwahanol i'r CKL cyfredol. Dilëwch y CKL cyfredol.
+sec-error-cert-not-in-name-space = Nid oes gan Awdurdod Tystysgrifo'r dystysgrif hon hawl i gyhoeddi tystysgrif yn yr enw hwn.
+sec-error-krl-not-yet-valid = Nid yw rhestr dileu'r allwedd ar gyfer y dystysgrif yn ddilys eto.
+sec-error-crl-not-yet-valid = Nid yw rhestr dileu'r dystysgrif ar gyfer y dystysgrif yn ddilys eto.
+sec-error-unknown-cert = Nid oedd modd canfod y dystysgrif ofynnol.
+sec-error-unknown-signer = Nid oedd modd canfod tystysgrif y llofnodwr.
+sec-error-cert-bad-access-location = Mae gan leoliad gweinydd statws y dystysgrif fformat annilys.
+sec-error-ocsp-unknown-response-type = Nid oes modd dadgodio ymateb OCSP yn llawn; mae o fath anhysbys.
+sec-error-ocsp-bad-http-response = Dychwelodd gweinydd OCSP ddata HTTP annisgwyl/annilys.
+sec-error-ocsp-malformed-request = Mae'r gweinydd OCSP wedi pennu'r cais fel un llwgr neu heb ei ffurfio'n gywir.
+sec-error-ocsp-server-error = Profodd y gweinydd OCSP wall mewnol.
+sec-error-ocsp-try-server-later = Mae gweinydd yr OCSP yn awgrymu y dylech geisio eto.
+sec-error-ocsp-request-needs-sig = Mae angen llofnod ar gyfer y gweinydd OCSP.
+sec-error-ocsp-unauthorized-request = Mae'r gweinydd OCSP wedi gwrthod y cais fel un anawdurdodedig.
+sec-error-ocsp-unknown-response-status = Dychwelodd y gweinydd OCSP statws heb ei gydnabod.
+sec-error-ocsp-unknown-cert = Nid oes gan y gweinydd OCSP statws ar gyfer y dystysgrif.
+sec-error-ocsp-not-enabled = Rhaid galluogi OCSP cyn cyflawni'r weithred.
+sec-error-ocsp-no-default-responder = Rhaid gosod ymatebwr rhagosodedig yr OCSP cyn cyflawni'r weithred.
+sec-error-ocsp-malformed-response = Roedd ymateb y gweinydd OCSP yn llwgr neu heb ei ffurfio'n gywir.
+sec-error-ocsp-unauthorized-response = Nid oes gan lofnodwr ymateb yr OCSP yr awdurdod i ddarparu statws y dystysgrif.
+sec-error-ocsp-future-response = Nid yw ymateb yr OCSP nyn ddilys eto (mae'n cynnwys dyddiad yn y dyfodol).
+sec-error-ocsp-old-response = Mae ymateb yr OCSP yn cynnwys hen ddata.
+sec-error-digest-not-found = Heb ganfod Crynodeb CMS neu PKCS #7 yn y neges gyda'r llofnod.
+sec-error-unsupported-message-type = Nid yw'r math o neges CMS neu PKCS #7 yn cael eu cynnal.
+sec-error-module-stuck = Nid oeddd modd tynnu modiwl PKCS #11 am ei fod yn cael ei ddefnyddio.
+sec-error-bad-template = Methu dadgodio data ASN.1. Roedd y templed yn annilys.
+sec-error-crl-not-found = Methu canfod CRL cytûn.
+sec-error-reused-issuer-and-serial = Rydych yn ceisio mewnforio tystysgrif gyda'r un cyhoeddwr/cyfres a'r dystysgrif gyfredol, ond nid yr un dystysgrif ydyw.
+sec-error-busy = Meddodd yr NSS â chau. Gwrthychau yn dal mewn defnydd.
+sec-error-extra-input = Mae'r neges DER amgodedig yn cynnwys data ychwanegol heb ei ddefnyddio.
+sec-error-unsupported-elliptic-curve = Cromlin eliptig heb ei gynnal.
+sec-error-unsupported-ec-point-form = Ffurf pwynt cromlin eliptig heb ei gynnal.
+sec-error-unrecognized-oid = Adnabyddwr Gwrthrychau Anhysbys.
+sec-error-ocsp-invalid-signing-cert = Tysytysgrif llofnodi OCSP anniltys yn ymateb yr OCSP.
+sec-error-revoked-certificate-crl = Mae'r dystysgrif wedi ei diddymu yn rhestr diddymu cyhoeddwr y dystysgrif.
+sec-error-revoked-certificate-ocsp = Mae tystysgrif adrodd ymatebion OCSP y cyhoeddwr wedi ei diddymu.
+sec-error-crl-invalid-version = Mae gan Rhestr Diddymu Tystysgrifau'r Cyhoeddwr rhif fersiwn anhysbys.
+sec-error-crl-v1-critical-extension = Mae gan Rhestr Diddymu Tystysgrif V1 y cyhoeddwr estyniad critigol.
+sec-error-crl-unknown-critical-extension = Mae gan Rhestr Diddymu Tystysgrif V2 y cyhoeddwr estyniad critigol anhysbys.
+sec-error-unknown-object-type = Gwrthrych o fath anhysbys wedi ei bennu.
+sec-error-incompatible-pkcs11 = Mae gyrrwr PKCS #11 yn tarfu'r manyleb mewn dull anghymarus.
+sec-error-no-event = Mae digwyddiad slot newydd ar gael ar hyn o bryd.
+sec-error-crl-already-exists = Mae'r CRL yn bodoli eisoes.
+sec-error-not-initialized = Nid yw'r NSS wedi ei gychwyn.
+sec-error-token-not-logged-in = Methodd y weithred gan nad yw tocyn PKCS#11 wedi ei fewngofnodi.
+sec-error-ocsp-responder-cert-invalid = Mae ffurfweddiad tystysgrif ymatebwr OCSP yn anilys.
+sec-error-ocsp-bad-signature = Mae gan ymateb yr OCSP lofnod annilys.
+sec-error-out-of-search-limits = Mae chwilio dilysu'r dystysgrif tu llan i derfynnau ei chwilio
+sec-error-invalid-policy-mapping = Mae mapio polisi yn cynnwys anypolicy
+sec-error-policy-validation-failed = Mae cadwyn y dystysgrif yn methu'r dilysiad polisi
+sec-error-unknown-aia-location-type = Math lleoliad anhysbys yn estyniad tystysgrif AIA
+sec-error-bad-http-response = Dychwelodd y gweinydd ymateb HTTP gwael
+sec-error-bad-ldap-response = Dychwelodd y gweinydd ymateb LDAP gwael
+sec-error-failed-to-encode-data = Methwyd amgosio data gydag amgodiwr ASN1
+sec-error-bad-info-access-location = Lleoliad mynediad gwybodaeth gwael mewn estyniad tystysgrif
+sec-error-libpkix-internal = Digwyddodd gwall mewnol libpkix yn ystod dilysiad tystysgrif.
+sec-error-pkcs11-general-error = Dychwelodd modiwl PKCS #11 CKR_GENERAL_ERROR, gan awgrymu fod gwall anadferadwy wedi digwydd.
+sec-error-pkcs11-function-failed = Dychwelodd PKCS #11 CKR_FUNCTION_FAILED, gan awgrymu nad oedd modd cyflawni'r swyddogaeth ofynnol. Efallai bydd cyflawni'r un weithred eto'n llwyddo.
+sec-error-pkcs11-device-error = Dychwelodd modiwl PKCS #11 CKR_DEVICE_ERROR, gan awgrymu fod yna broblem gyda'r tocyn neu'r slot.
+sec-error-bad-info-access-method = Dull mynediad gwybodaeth anhysbys mewn estyniad tystysgrif.
+sec-error-crl-import-failed = Gwall wrth geisio mewnforio CRL.
+sec-error-expired-password = Mae'r cyfrinair wedi dod i ben.
+sec-error-locked-password = Mae'r cyfrinair wedi ei gloi.
+sec-error-unknown-pkcs11-error = Gwall PKCS #11 anhysbys.
+sec-error-bad-crl-dp-url = URL annilys neu heb ei gynnal yn enw pwynt dosbarthiad CRL.
+sec-error-cert-signature-algorithm-disabled = Cafodd y dystysgrif ei llofnodi gan ddefnyddio algorithm llofnod sydd wedi ei analluogi am nad yw'n ddiogel.
+
+mozilla-pkix-error-key-pinning-failure = Mae'r gweinydd yn defnyddio pinio allwedd (HPKP) ond nid oedd modd cynhyrchu cadwyn tystysgrif ymddiriedig sy'n cyd-fynd a'r set pinnau. Nid oes mod gwrthwneud torri pinio allweddi.
+mozilla-pkix-error-ca-cert-used-as-end-entity = Mae'r gweinydd yn defnyddio tystysgrif gydag estyniad cyfyngiadau sylfaenol sy'n ei ddynodi fel yr awdurdod tystysgrifo. Ar gyfer tystysgrifau sydd wedi eu rhyddhau'n briodol, ni ddylai hyn fod yn wir.
+mozilla-pkix-error-inadequate-key-size = Cyflwynodd y gweinydd dystysgrif sydd ag allwedd sy'n rhy fach i greu cysylltiad diogel.
+mozilla-pkix-error-v1-cert-used-as-ca = Defnyddiwyd tystysgrif X.509 fersiwn 1 nad yw'n angor ymddiriedaeth i gyhoeddi tystysgrif y wefan. Mae tystysgrifau X.509 fersiwn 1 yn anghymeradwy ac ni ddylent gael eu defnyddio i lofnodi tystysgrifau eraill.
+mozilla-pkix-error-not-yet-valid-certificate = Cyflwynodd y gweinydd dystysgrif nad yw eto'n ddilys.
+mozilla-pkix-error-not-yet-valid-issuer-certificate = Defnyddiwyd tystysgrif nad yw eto'n ddilys i gyhoeddi tystysgrif y gweinydd.
+mozilla-pkix-error-signature-algorithm-mismatch = Nid yw'r algorithm llofnod ym maes llofnod y dystysgrif yn cyd-fynd â'r algorithm ym maes signatureAlgorithm.
+mozilla-pkix-error-ocsp-response-for-cert-missing = Nid yw ymateb yr OCSP yn cynnwys statws y dystysgrif sy'n cael ei gwirio.
+mozilla-pkix-error-validity-too-long = Cyflwynodd y gweinydd dystysgrif sy'n ddilys am rhy hir.
+mozilla-pkix-error-required-tls-feature-missing = Mae'r nodwedd TLS angenrheidiol ar goll.
+mozilla-pkix-error-invalid-integer-encoding = Cyflwynodd y gweinydd dystysgrif sy'n cynnwys math annilys o amgodio integer. Mae'r rhesymau cyffredin yn cynnwys rhifau cyfresol negyddol, moduli RSA negyddol, ac amgodio nad ydynt eu hangen bellach.
+mozilla-pkix-error-empty-issuer-name = Cyflwynodd y gweinydd dystysgrif gydag enw cyhoeddwr penodol gwag.
+mozilla-pkix-error-additional-policy-constraint-failed = Methodd cyfyngiad polisi ychwanegol wrth ddilysu'r dystysgrif hon.
+mozilla-pkix-error-self-signed-cert = Nid oes modd ymddiried yn y dystysgrif am ei fod wedi ei hunanlofnodi.
+
+xp-java-remove-principal-error = Methu tynnu'r prif
+xp-java-delete-privilege-error = Methu dileu'r fraint
+xp-java-cert-not-exists-error = Nid oes gan y prif dystysgrif
+
+xp-sec-fortezza-bad-card = Nid yw cerdyn Fortezza wedi ei gychwyn yn gywir. Tynnwch y cerdyn a'i ddychwelyd ar y cyhoeddwr.
+xp-sec-fortezza-no-card = Heb ganfod cerdyn Fortezza
+xp-sec-fortezza-none-selected = Heb ddewis cerdyn Fortezza
+xp-sec-fortezza-more-info = Dewiswch bersonoliaeth i dderbyn mwy o wybodaeth amdano
+xp-sec-fortezza-person-not-found = Heb ddarganfod personoliaeth
+xp-sec-fortezza-no-more-info = Dim rhagor o wybodaeth ar Personoliaeth hwnnw
+xp-sec-fortezza-bad-pin = Pin annilys
+xp-sec-fortezza-person-error = Methu cychwyn personoliaethau Fortezza.
diff --git a/thunderbird-l10n/cy/localization/cy/toolkit/passwordmgr/passwordmgr.ftl b/thunderbird-l10n/cy/localization/cy/toolkit/passwordmgr/passwordmgr.ftl
new file mode 100644
index 0000000000..0358839f55
--- /dev/null
+++ b/thunderbird-l10n/cy/localization/cy/toolkit/passwordmgr/passwordmgr.ftl
@@ -0,0 +1,39 @@
+# This Source Code Form is subject to the terms of the Mozilla Public
+# License, v. 2.0. If a copy of the MPL was not distributed with this
+# file, You can obtain one at http://mozilla.org/MPL/2.0/.
+
+
+## Save and update password doorhanger
+
+# Variables
+#   $host (String) - Hostname for which the password is saved for.
+password-manager-save-password-message = Cadw cyfrinair { $host }?
+password-manager-save-password-button-deny =
+    .label = Nid nawr
+    .accesskey = N
+password-manager-save-password-button-allow =
+    .label = Cadw
+    .accesskey = C
+password-manager-save-password-button-never =
+    .label = Peidio Byth â Chadw
+    .accesskey = P
+# Variables
+#   $host (String) - Hostname for which the password is updated for.
+password-manager-update-password-message = Diweddaru cyfrinair { $host }?
+password-manager-update-password-button-delete =
+    .label = Tynnu'r cyfrinair sydd wedi'i gadw
+    .accesskey = T
+password-manager-update-login-add-username = Ychwanegu enw defnyddiwr i gyfrinair wedi’i gadw?
+password-manager-password-password-button-allow =
+    .label = Diweddaru
+    .accesskey = i
+password-manager-update-password-button-deny =
+    .label = Peidio â Diweddaru
+    .accesskey = P
+# This is displayed in place of the username when it is missing.
+password-manager-no-username-placeholder = Dim enw defnyddiwr
+password-manager-toggle-password =
+    .label = Dangos cyfrinair
+    .accesskey = d
+password-manager-confirm-password-change = Cadarnhau Newid Cyfrinair
+password-manager-select-username = Dewis pa fewngofnod i'w ddiweddaru:
diff --git a/thunderbird-l10n/cy/localization/cy/toolkit/payments/payments.ftl b/thunderbird-l10n/cy/localization/cy/toolkit/payments/payments.ftl
new file mode 100644
index 0000000000..fc93b145fb
--- /dev/null
+++ b/thunderbird-l10n/cy/localization/cy/toolkit/payments/payments.ftl
@@ -0,0 +1,51 @@
+# This Source Code Form is subject to the terms of the Mozilla Public
+# License, v. 2.0. If a copy of the MPL was not distributed with this
+# file, You can obtain one at http://mozilla.org/MPL/2.0/.
+
+
+# This value isn't used directly, but is defined to avoid duplication
+# in the "credit-card-label-*" strings.
+#
+# Variables:
+#   $month (String): Numeric month the credit card expires
+#   $year (String): Four-digit year the credit card expires
+credit-card-expiration = Yn dod i ben ar { $month }/{ $year }
+
+## These labels serve as a description of a credit card.
+## The description must include a credit card number, and may optionally
+## include a cardholder name, an expiration date, or both, so we have
+## four variations.
+
+# Label for a credit card with a number only
+#
+# Variables:
+#   $number (String): Partially-redacted credit card number
+#   $type (String): Credit card type
+credit-card-label-number-2 = { $number }
+    .aria-label = { $type } { credit-card-label-number-2 }
+
+# Label for a credit card with a number and name
+#
+# Variables:
+#   $number (String): Partially-redacted credit card number
+#   $name (String): Cardholder name
+#   $type (String): Credit card type
+credit-card-label-number-name-2 = { $number }, { $name }
+    .aria-label = { $type } { credit-card-label-number-name-2 }
+
+# Label for a credit card with a number and expiration date
+#
+# Variables:
+#   $number (String): Partially-redacted credit card number
+#   $type (String): Credit card type
+credit-card-label-number-expiration-2 = { $number }, { credit-card-expiration }
+    .aria-label = { $type } { credit-card-label-number-expiration-2 }
+
+# Label for a credit card with a number, name, and expiration date
+#
+# Variables:
+#   $number (String): Partially-redacted credit card number
+#   $name (String): Cardholder name
+#   $type (String): Credit card type
+credit-card-label-number-name-expiration-2 = { $number }, { $name }, { credit-card-expiration }
+    .aria-label = { $type } { credit-card-label-number-name-expiration-2 }
diff --git a/thunderbird-l10n/cy/localization/cy/toolkit/pdfviewer/viewer.ftl b/thunderbird-l10n/cy/localization/cy/toolkit/pdfviewer/viewer.ftl
new file mode 100644
index 0000000000..9931629270
--- /dev/null
+++ b/thunderbird-l10n/cy/localization/cy/toolkit/pdfviewer/viewer.ftl
@@ -0,0 +1,392 @@
+# This Source Code Form is subject to the terms of the Mozilla Public
+# License, v. 2.0. If a copy of the MPL was not distributed with this
+# file, You can obtain one at http://mozilla.org/MPL/2.0/.
+
+
+## Main toolbar buttons (tooltips and alt text for images)
+
+pdfjs-previous-button =
+    .title = Tudalen Flaenorol
+pdfjs-previous-button-label = Blaenorol
+pdfjs-next-button =
+    .title = Tudalen Nesaf
+pdfjs-next-button-label = Nesaf
+# .title: Tooltip for the pageNumber input.
+pdfjs-page-input =
+    .title = Tudalen
+# Variables:
+#   $pagesCount (Number) - the total number of pages in the document
+# This string follows an input field with the number of the page currently displayed.
+pdfjs-of-pages = o { $pagesCount }
+# Variables:
+#   $pageNumber (Number) - the currently visible page
+#   $pagesCount (Number) - the total number of pages in the document
+pdfjs-page-of-pages = ({ $pageNumber } o { $pagesCount })
+pdfjs-zoom-out-button =
+    .title = Chwyddo Allan
+pdfjs-zoom-out-button-label = Chwyddo Allan
+pdfjs-zoom-in-button =
+    .title = Chwyddo Mewn
+pdfjs-zoom-in-button-label = Chwyddo Mewn
+pdfjs-zoom-select =
+    .title = Chwyddo
+pdfjs-presentation-mode-button =
+    .title = Newid i'r Modd Cyflwyno
+pdfjs-presentation-mode-button-label = Modd Cyflwyno
+pdfjs-open-file-button =
+    .title = Agor Ffeil
+pdfjs-open-file-button-label = Agor
+pdfjs-print-button =
+    .title = Argraffu
+pdfjs-print-button-label = Argraffu
+pdfjs-save-button =
+    .title = Cadw
+pdfjs-save-button-label = Cadw
+# Used in Firefox for Android as a tooltip for the download button (“download” is a verb).
+pdfjs-download-button =
+    .title = Llwytho i Lawr
+# Used in Firefox for Android as a label for the download button (“download” is a verb).
+# Length of the translation matters since we are in a mobile context, with limited screen estate.
+pdfjs-download-button-label = Llwytho i Lawr
+pdfjs-bookmark-button =
+    .title = Tudalen Gyfredol (Gweld URL o'r Dudalen Gyfredol)
+pdfjs-bookmark-button-label = Tudalen Gyfredol
+# Used in Firefox for Android.
+pdfjs-open-in-app-button =
+    .title = Agor yn yr ap
+# Used in Firefox for Android.
+# Length of the translation matters since we are in a mobile context, with limited screen estate.
+pdfjs-open-in-app-button-label = Agor yn yr ap
+
+##  Secondary toolbar and context menu
+
+pdfjs-tools-button =
+    .title = Offer
+pdfjs-tools-button-label = Offer
+pdfjs-first-page-button =
+    .title = Mynd i'r Dudalen Gyntaf
+pdfjs-first-page-button-label = Mynd i'r Dudalen Gyntaf
+pdfjs-last-page-button =
+    .title = Mynd i'r Dudalen Olaf
+pdfjs-last-page-button-label = Mynd i'r Dudalen Olaf
+pdfjs-page-rotate-cw-button =
+    .title = Cylchdroi Clocwedd
+pdfjs-page-rotate-cw-button-label = Cylchdroi Clocwedd
+pdfjs-page-rotate-ccw-button =
+    .title = Cylchdroi Gwrthglocwedd
+pdfjs-page-rotate-ccw-button-label = Cylchdroi Gwrthglocwedd
+pdfjs-cursor-text-select-tool-button =
+    .title = Galluogi Dewis Offeryn Testun
+pdfjs-cursor-text-select-tool-button-label = Offeryn Dewis Testun
+pdfjs-cursor-hand-tool-button =
+    .title = Galluogi Offeryn Llaw
+pdfjs-cursor-hand-tool-button-label = Offeryn Llaw
+pdfjs-scroll-page-button =
+    .title = Defnyddio Sgrolio Tudalen
+pdfjs-scroll-page-button-label = Sgrolio Tudalen
+pdfjs-scroll-vertical-button =
+    .title = Defnyddio Sgrolio Fertigol
+pdfjs-scroll-vertical-button-label = Sgrolio Fertigol
+pdfjs-scroll-horizontal-button =
+    .title = Defnyddio Sgrolio Llorweddol
+pdfjs-scroll-horizontal-button-label = Sgrolio Llorweddol
+pdfjs-scroll-wrapped-button =
+    .title = Defnyddio Sgrolio Amlapio
+pdfjs-scroll-wrapped-button-label = Sgrolio Amlapio
+pdfjs-spread-none-button =
+    .title = Peidio uno trawsdaleniadau
+pdfjs-spread-none-button-label = Dim Trawsdaleniadau
+pdfjs-spread-odd-button =
+    .title = Uno trawsdaleniadau gan gychwyn gyda thudalennau odrif
+pdfjs-spread-odd-button-label = Trawsdaleniadau Odrif
+pdfjs-spread-even-button =
+    .title = Uno trawsdaleniadau gan gychwyn gyda thudalennau eilrif
+pdfjs-spread-even-button-label = Trawsdaleniadau Eilrif
+
+## Document properties dialog
+
+pdfjs-document-properties-button =
+    .title = Priodweddau Dogfen…
+pdfjs-document-properties-button-label = Priodweddau Dogfen…
+pdfjs-document-properties-file-name = Enw ffeil:
+pdfjs-document-properties-file-size = Maint ffeil:
+# Variables:
+#   $size_kb (Number) - the PDF file size in kilobytes
+#   $size_b (Number) - the PDF file size in bytes
+pdfjs-document-properties-kb = { $size_kb } KB ({ $size_b } beit)
+# Variables:
+#   $size_mb (Number) - the PDF file size in megabytes
+#   $size_b (Number) - the PDF file size in bytes
+pdfjs-document-properties-mb = { $size_mb } MB ({ $size_b } beit)
+pdfjs-document-properties-title = Teitl:
+pdfjs-document-properties-author = Awdur:
+pdfjs-document-properties-subject = Pwnc:
+pdfjs-document-properties-keywords = Allweddair:
+pdfjs-document-properties-creation-date = Dyddiad Creu:
+pdfjs-document-properties-modification-date = Dyddiad Addasu:
+# Variables:
+#   $date (Date) - the creation/modification date of the PDF file
+#   $time (Time) - the creation/modification time of the PDF file
+pdfjs-document-properties-date-string = { $date }, { $time }
+pdfjs-document-properties-creator = Crewr:
+pdfjs-document-properties-producer = Cynhyrchydd PDF:
+pdfjs-document-properties-version = Fersiwn PDF:
+pdfjs-document-properties-page-count = Cyfrif Tudalen:
+pdfjs-document-properties-page-size = Maint Tudalen:
+pdfjs-document-properties-page-size-unit-inches = o fewn
+pdfjs-document-properties-page-size-unit-millimeters = mm
+pdfjs-document-properties-page-size-orientation-portrait = portread
+pdfjs-document-properties-page-size-orientation-landscape = tirlun
+pdfjs-document-properties-page-size-name-a-three = A3
+pdfjs-document-properties-page-size-name-a-four = A4
+pdfjs-document-properties-page-size-name-letter = Llythyr
+pdfjs-document-properties-page-size-name-legal = Cyfreithiol
+
+## Variables:
+##   $width (Number) - the width of the (current) page
+##   $height (Number) - the height of the (current) page
+##   $unit (String) - the unit of measurement of the (current) page
+##   $name (String) - the name of the (current) page
+##   $orientation (String) - the orientation of the (current) page
+
+pdfjs-document-properties-page-size-dimension-string = { $width } × { $height } { $unit } ({ $orientation })
+pdfjs-document-properties-page-size-dimension-name-string = { $width } × { $height } { $unit } ({ $name }, { $orientation })
+
+##
+
+# The linearization status of the document; usually called "Fast Web View" in
+# English locales of Adobe software.
+pdfjs-document-properties-linearized = Golwg Gwe Cyflym:
+pdfjs-document-properties-linearized-yes = Iawn
+pdfjs-document-properties-linearized-no = Na
+pdfjs-document-properties-close-button = Cau
+
+## Print
+
+pdfjs-print-progress-message = Paratoi dogfen ar gyfer ei hargraffu…
+# Variables:
+#   $progress (Number) - percent value
+pdfjs-print-progress-percent = { $progress }%
+pdfjs-print-progress-close-button = Diddymu
+pdfjs-printing-not-supported = Rhybudd: Nid yw argraffu yn cael ei gynnal yn llawn gan y porwr.
+pdfjs-printing-not-ready = Rhybudd: Nid yw'r PDF wedi ei lwytho'n llawn ar gyfer argraffu.
+
+## Tooltips and alt text for side panel toolbar buttons
+
+pdfjs-toggle-sidebar-button =
+    .title = Toglo'r Bar Ochr
+pdfjs-toggle-sidebar-notification-button =
+    .title = Toglo'r Bar Ochr (mae'r ddogfen yn cynnwys amlinelliadau/atodiadau/haenau)
+pdfjs-toggle-sidebar-button-label = Toglo'r Bar Ochr
+pdfjs-document-outline-button =
+    .title = Dangos Amlinell Dogfen (clic dwbl i ymestyn/cau pob eitem)
+pdfjs-document-outline-button-label = Amlinelliad Dogfen
+pdfjs-attachments-button =
+    .title = Dangos Atodiadau
+pdfjs-attachments-button-label = Atodiadau
+pdfjs-layers-button =
+    .title = Dangos Haenau (cliciwch ddwywaith i ailosod yr holl haenau i'r cyflwr rhagosodedig)
+pdfjs-layers-button-label = Haenau
+pdfjs-thumbs-button =
+    .title = Dangos Lluniau Bach
+pdfjs-thumbs-button-label = Lluniau Bach
+pdfjs-current-outline-item-button =
+    .title = Canfod yr Eitem Amlinellol Gyfredol
+pdfjs-current-outline-item-button-label = Yr Eitem Amlinellol Gyfredol
+pdfjs-findbar-button =
+    .title = Canfod yn y Ddogfen
+pdfjs-findbar-button-label = Canfod
+pdfjs-additional-layers = Haenau Ychwanegol
+
+## Thumbnails panel item (tooltip and alt text for images)
+
+# Variables:
+#   $page (Number) - the page number
+pdfjs-thumb-page-title =
+    .title = Tudalen { $page }
+# Variables:
+#   $page (Number) - the page number
+pdfjs-thumb-page-canvas =
+    .aria-label = Llun Bach Tudalen { $page }
+
+## Find panel button title and messages
+
+pdfjs-find-input =
+    .title = Canfod
+    .placeholder = Canfod yn y ddogfen…
+pdfjs-find-previous-button =
+    .title = Canfod enghraifft flaenorol o'r ymadrodd
+pdfjs-find-previous-button-label = Blaenorol
+pdfjs-find-next-button =
+    .title = Canfod enghraifft nesaf yr ymadrodd
+pdfjs-find-next-button-label = Nesaf
+pdfjs-find-highlight-checkbox = Amlygu Popeth
+pdfjs-find-match-case-checkbox-label = Cydweddu Maint
+pdfjs-find-match-diacritics-checkbox-label = Diacritigau Cyfatebol
+pdfjs-find-entire-word-checkbox-label = Geiriau Cyfan
+pdfjs-find-reached-top = Wedi cyrraedd brig y dudalen, parhau o'r gwaelod
+pdfjs-find-reached-bottom = Wedi cyrraedd diwedd y dudalen, parhau o'r brig
+# Variables:
+#   $current (Number) - the index of the currently active find result
+#   $total (Number) - the total number of matches in the document
+pdfjs-find-match-count =
+    { $total ->
+        [zero] { $current } o { $total } cydweddiadau
+        [one] { $current } o { $total } cydweddiad
+        [two] { $current } o { $total } gydweddiad
+        [few] { $current } o { $total } cydweddiad
+        [many] { $current } o { $total } chydweddiad
+       *[other] { $current } o { $total } cydweddiad
+    }
+# Variables:
+#   $limit (Number) - the maximum number of matches
+pdfjs-find-match-count-limit =
+    { $limit ->
+        [zero] Mwy nag { $limit } cydweddiadau
+        [one] Mwy nag { $limit } cydweddiad
+        [two] Mwy nag { $limit } gydweddiad
+        [few] Mwy nag { $limit } cydweddiad
+        [many] Mwy nag { $limit } chydweddiad
+       *[other] Mwy nag { $limit } cydweddiad
+    }
+pdfjs-find-not-found = Heb ganfod ymadrodd
+
+## Predefined zoom values
+
+pdfjs-page-scale-width = Lled Tudalen
+pdfjs-page-scale-fit = Ffit Tudalen
+pdfjs-page-scale-auto = Chwyddo Awtomatig
+pdfjs-page-scale-actual = Maint Gwirioneddol
+# Variables:
+#   $scale (Number) - percent value for page scale
+pdfjs-page-scale-percent = { $scale }%
+
+## PDF page
+
+# Variables:
+#   $page (Number) - the page number
+pdfjs-page-landmark =
+    .aria-label = Tudalen { $page }
+
+## Loading indicator messages
+
+pdfjs-loading-error = Digwyddodd gwall wrth lwytho'r PDF.
+pdfjs-invalid-file-error = Ffeil PDF annilys neu llwgr.
+pdfjs-missing-file-error = Ffeil PDF coll.
+pdfjs-unexpected-response-error = Ymateb annisgwyl gan y gweinydd.
+pdfjs-rendering-error = Digwyddodd gwall wrth adeiladu'r dudalen.
+
+## Annotations
+
+# Variables:
+#   $date (Date) - the modification date of the annotation
+#   $time (Time) - the modification time of the annotation
+pdfjs-annotation-date-string = { $date }, { $time }
+# .alt: This is used as a tooltip.
+# Variables:
+#   $type (String) - an annotation type from a list defined in the PDF spec
+# (32000-1:2008 Table 169 – Annotation types).
+# Some common types are e.g.: "Check", "Text", "Comment", "Note"
+pdfjs-text-annotation-type =
+    .alt = [Anodiad { $type } ]
+
+## Password
+
+pdfjs-password-label = Rhowch gyfrinair i agor y PDF.
+pdfjs-password-invalid = Cyfrinair annilys. Ceisiwch eto.
+pdfjs-password-ok-button = Iawn
+pdfjs-password-cancel-button = Diddymu
+pdfjs-web-fonts-disabled = Ffontiau gwe wedi eu hanalluogi: methu defnyddio ffontiau PDF mewnblanedig.
+
+## Editing
+
+pdfjs-editor-free-text-button =
+    .title = Testun
+pdfjs-editor-free-text-button-label = Testun
+pdfjs-editor-ink-button =
+    .title = Lluniadu
+pdfjs-editor-ink-button-label = Lluniadu
+pdfjs-editor-stamp-button =
+    .title = Ychwanegu neu olygu delweddau
+pdfjs-editor-stamp-button-label = Ychwanegu neu olygu delweddau
+pdfjs-editor-remove-button =
+    .title = Tynnu
+
+## Remove button for the various kind of editor.
+
+pdfjs-editor-remove-ink-button =
+    .title = Dileu lluniad
+pdfjs-editor-remove-freetext-button =
+    .title = Dileu testun
+pdfjs-editor-remove-stamp-button =
+    .title = Dileu delwedd
+pdfjs-editor-remove-highlight-button =
+    .title = Tynnu amlygiad
+
+##
+
+# Editor Parameters
+pdfjs-editor-free-text-color-input = Lliw
+pdfjs-editor-free-text-size-input = Maint
+pdfjs-editor-ink-color-input = Lliw
+pdfjs-editor-ink-thickness-input = Trwch
+pdfjs-editor-ink-opacity-input = Didreiddedd
+pdfjs-editor-stamp-add-image-button =
+    .title = Ychwanegu delwedd
+pdfjs-editor-stamp-add-image-button-label = Ychwanegu delwedd
+pdfjs-free-text =
+    .aria-label = Golygydd Testun
+pdfjs-free-text-default-content = Cychwyn teipio…
+pdfjs-ink =
+    .aria-label = Golygydd Lluniadu
+pdfjs-ink-canvas =
+    .aria-label = Delwedd wedi'i chreu gan ddefnyddwyr
+
+## Alt-text dialog
+
+# Alternative text (alt text) helps when people can't see the image.
+pdfjs-editor-alt-text-button-label = Testun amgen (alt)
+pdfjs-editor-alt-text-edit-button-label = Golygu testun amgen
+pdfjs-editor-alt-text-dialog-label = Dewisiadau
+pdfjs-editor-alt-text-dialog-description = Mae testun amgen (testun alt) yn helpu pan na all pobl weld y ddelwedd neu pan nad yw'n llwytho.
+pdfjs-editor-alt-text-add-description-label = Ychwanegu disgrifiad
+pdfjs-editor-alt-text-add-description-description = Anelwch at 1-2 frawddeg sy'n disgrifio'r pwnc, y cefndir neu'r gweithredoedd.
+pdfjs-editor-alt-text-mark-decorative-label = Marcio fel addurniadol
+pdfjs-editor-alt-text-mark-decorative-description = Mae'n cael ei ddefnyddio ar gyfer delweddau addurniadol, fel borderi neu farciau dŵr.
+pdfjs-editor-alt-text-cancel-button = Diddymu
+pdfjs-editor-alt-text-save-button = Cadw
+pdfjs-editor-alt-text-decorative-tooltip = Marcio fel addurniadol
+# .placeholder: This is a placeholder for the alt text input area
+pdfjs-editor-alt-text-textarea =
+    .placeholder = Er enghraifft, “Mae dyn ifanc yn eistedd wrth fwrdd i fwyta pryd bwyd”
+
+## Editor resizers
+## This is used in an aria label to help to understand the role of the resizer.
+
+pdfjs-editor-resizer-label-top-left = Y gornel chwith uchaf — newid maint
+pdfjs-editor-resizer-label-top-middle = Canol uchaf - newid maint
+pdfjs-editor-resizer-label-top-right = Y gornel dde uchaf - newid maint
+pdfjs-editor-resizer-label-middle-right = De canol - newid maint
+pdfjs-editor-resizer-label-bottom-right = Y gornel dde isaf — newid maint
+pdfjs-editor-resizer-label-bottom-middle = Canol gwaelod — newid maint
+pdfjs-editor-resizer-label-bottom-left = Y gornel chwith isaf — newid maint
+pdfjs-editor-resizer-label-middle-left = Chwith canol — newid maint
+
+## Color picker
+
+# This means "Color used to highlight text"
+pdfjs-editor-highlight-colorpicker-label = Lliw amlygu
+pdfjs-editor-colorpicker-button =
+    .title = Newid lliw
+pdfjs-editor-colorpicker-dropdown =
+    .aria-label = Dewisiadau lliw
+pdfjs-editor-colorpicker-yellow =
+    .title = Melyn
+pdfjs-editor-colorpicker-green =
+    .title = Gwyrdd
+pdfjs-editor-colorpicker-blue =
+    .title = Glas
+pdfjs-editor-colorpicker-pink =
+    .title = Pinc
+pdfjs-editor-colorpicker-red =
+    .title = Coch
diff --git a/thunderbird-l10n/cy/localization/cy/toolkit/pictureinpicture/pictureinpicture.ftl b/thunderbird-l10n/cy/localization/cy/toolkit/pictureinpicture/pictureinpicture.ftl
new file mode 100644
index 0000000000..9295f2f886
--- /dev/null
+++ b/thunderbird-l10n/cy/localization/cy/toolkit/pictureinpicture/pictureinpicture.ftl
@@ -0,0 +1,86 @@
+# This Source Code Form is subject to the terms of the Mozilla Public
+# License, v. 2.0. If a copy of the MPL was not distributed with this
+# file, You can obtain one at http://mozilla.org/MPL/2.0/.
+
+pictureinpicture-player-title = Llun mewn Llun
+
+## Variables:
+##   $shortcut (String) - Keyboard shortcut to execute the command.
+
+## Note that this uses .tooltip rather than the standard '.title'
+## or '.tooltiptext' -  but it has the same effect. Code in the
+## picture-in-picture window will read and copy this to an in-document
+## DOM node that then shows the tooltip.
+##
+## Variables:
+##   $shortcut (String) - Keyboard shortcut to execute the command.
+
+pictureinpicture-pause-btn =
+    .aria-label = Oedi
+    .tooltip = Oedi (Bar Bylchu)
+pictureinpicture-play-btn =
+    .aria-label = Chwarae
+    .tooltip = Chwarae (Bar Bylchu)
+
+pictureinpicture-mute-btn =
+    .aria-label = Tewi
+    .tooltip = Tewi ({ $shortcut })
+pictureinpicture-unmute-btn =
+    .aria-label = Dad-dewi
+    .tooltip = Dad-dewi ({ $shortcut })
+
+pictureinpicture-unpip-btn =
+    .aria-label = Anfon nôl i'r tab
+    .tooltip = Nôl i'r tab
+
+pictureinpicture-close-btn =
+    .aria-label = Cau
+    .tooltip = Cau ({ $shortcut })
+
+pictureinpicture-subtitles-btn =
+    .aria-label = Is-deitlau
+    .tooltip = Is-deitlau
+
+pictureinpicture-fullscreen-btn2 =
+    .aria-label = Sgrin Lawn
+    .tooltip = Sgrin Lawn (clic dwbl neu { $shortcut })
+
+pictureinpicture-exit-fullscreen-btn2 =
+    .aria-label = Gadael sgrin lawn
+    .tooltip = Gadael sgrin lawn (clic dwbl neu { $shortcut })
+
+##
+
+# Keyboard shortcut to toggle fullscreen mode when Picture-in-Picture is open.
+pictureinpicture-toggle-fullscreen-shortcut =
+    .key = F
+
+## Note that this uses .tooltip rather than the standard '.title'
+## or '.tooltiptext' -  but it has the same effect. Code in the
+## picture-in-picture window will read and copy this to an in-document
+## DOM node that then shows the tooltip.
+
+pictureinpicture-seekbackward-btn =
+    .aria-label = Mynd yn ôl
+    .tooltip = Mynd yn ôl (←)
+
+pictureinpicture-seekforward-btn =
+    .aria-label = Ymlaen
+    .tooltip = Ymlaen (→)
+
+##
+
+# This string is never displayed on the window. Is intended to be announced by
+# a screen reader whenever a user opens the subtitles settings panel
+# after selecting the subtitles button.
+pictureinpicture-subtitles-panel-accessible = Gosodiadau isdeitlau
+
+pictureinpicture-subtitles-label = Is-deitlau
+
+pictureinpicture-font-size-label = Maint ffont
+
+pictureinpicture-font-size-small = Bach
+
+pictureinpicture-font-size-medium = Canolig
+
+pictureinpicture-font-size-large = Mawr
diff --git a/thunderbird-l10n/cy/localization/cy/toolkit/preferences/preferences.ftl b/thunderbird-l10n/cy/localization/cy/toolkit/preferences/preferences.ftl
new file mode 100644
index 0000000000..88855d2025
--- /dev/null
+++ b/thunderbird-l10n/cy/localization/cy/toolkit/preferences/preferences.ftl
@@ -0,0 +1,39 @@
+# This Source Code Form is subject to the terms of the Mozilla Public
+# License, v. 2.0. If a copy of the MPL was not distributed with this
+# file, You can obtain one at http://mozilla.org/MPL/2.0/.
+
+password-not-set =
+    .value = (heb ei osod)
+
+failed-pp-change = Methu newid y Prif Gyfrinair.
+incorrect-pp = Nid ydych wedi rhoi'r Prif Gyfrinair cyfredol cywir. Ceisiwch eto.
+pp-change-ok = Mae'r Prif Gyfrinair wedi ei newid yn llwyddiannus.
+
+settings-pp-erased-ok = Rydych wedi dileu eich Prif Gyfrinair. Ni fydd cyfrineiriau wedi'u storio ac allweddi preifat tystysgrif sy'n cael ei reoli gan { -brand-short-name } yn cael eu diogelu.
+settings-pp-not-wanted = Rhybudd! Rydych wedi penderfynu peidio â defnyddio Prif Gyfrinair. Ni fydd cyfrineiriau wedi'u storio ac allweddi preifat tystysgrif sy'n cael eu rheoli gan { -brand-short-name } yn cael eu diogelu.
+
+pp-change2empty-in-fips-mode = Rydych ym modd FIPS. Mae FIPS angen Prif Gyfrinair nad yw'n wag.
+pw-change-success-title = Llwyddo i Newid eich Cyfrinair
+pw-change-failed-title = Methu Newid eich Cyfrinair
+pw-remove-button =
+    .label = Tynnu
+
+primary-password-dialog =
+    .title = Prif Gyfrinair
+set-password-old-password = Cyfrinair cyfredol:
+set-password-new-password = Rhoi'r cyfrinair newydd:
+set-password-reenter-password = Rhoi'r cyfrinair eto:
+set-password-meter = Mesurydd ansawdd y cyfrinair
+set-password-meter-loading = Llwytho
+primary-password-admin = Mae eich gweinyddwr yn mynnu bod gennych Brif Gyfrinair wedi'i osod er mwyn cadw mewngofnodion a chyfrineiriau.
+primary-password-description = Mae Prif Gyfrinair yn cael ei ddefnyddio i ddiogelu gwybodaeth sensitif fel cyfrineiriau gwefannau.  Os fyddwch yn creu Prif Gyfrinair bydd gofyn i chi ei rhoi unwaith y sesiwn pan fydd { -brand-short-name } yn estyn gwybodaeth wedi ei gadw'n ddiogel gan y cyfrinair.
+primary-password-warning = Gwnewch yn siŵr eich bod yn cofio'r Prif Gyfrinair.  Os byddwch yn anghofio eich Prif Gyfieithiad, ni fydd modd i chi gael mynediad at unrhyw wybodaeth mae'n ei ddiogelu.
+
+remove-primary-password =
+    .title = Tynnu'r Prif Gyfrinair
+remove-info =
+    .value = Rhaid rhoi eich cyfrinair presennol cyn parhau:
+remove-primary-password-warning1 = Mae eich Prif Gyfrinair yn cael ei ddefnyddio i ddiogelu data sensitif fel cyfrineiriau gwefannau.
+remove-primary-password-warning2 = Os byddwch yn tynnu eich Prif Gyfrinair ni fydd eich gwybodaeth wedi ei ddiogelu os yw eich cyfrifiadur wedi ei gyfaddawdu.
+remove-password-old-password =
+    .value = Cyfrinair cyfredol:
diff --git a/thunderbird-l10n/cy/localization/cy/toolkit/printing/printDialogs.ftl b/thunderbird-l10n/cy/localization/cy/toolkit/printing/printDialogs.ftl
new file mode 100644
index 0000000000..8b1635c5a6
--- /dev/null
+++ b/thunderbird-l10n/cy/localization/cy/toolkit/printing/printDialogs.ftl
@@ -0,0 +1,112 @@
+# This Source Code Form is subject to the terms of the Mozilla Public
+# License, v. 2.0. If a copy of the MPL was not distributed with this
+# file, You can obtain one at http://mozilla.org/MPL/2.0/.
+
+print-setup =
+    .title = Gosodiad Tudalen
+custom-prompt-title = Cyfaddasu…
+custom-prompt-prompt = Rhowch destun pennyn /troedyn cyfaddas
+basic-tab =
+    .label = Fformatio a Dewisiadau
+advanced-tab =
+    .label = Ymylon a Phennyn/Troedyn
+format-group-label =
+    .value = Fformat
+orientation-label =
+    .value = Cyfeiriadaeth:
+portrait =
+    .label = Portread
+    .accesskey = P
+landscape =
+    .label = Tirlun
+    .accesskey = T
+scale =
+    .label = Graddfa:
+    .accesskey = r
+scale-percent =
+    .value = %
+shrink-to-fit =
+    .label = Cywasgu i Led y Dudalen
+    .accesskey = L
+options-group-label =
+    .value = Dewisiadau
+print-bg =
+    .label = Argraffu Lliwiau'r Cefndir (lliwiau a delweddau)
+    .accesskey = A
+margin-group-label-inches =
+    .value = Ymylon (modfedd)
+margin-group-label-metric =
+    .value = Ymylon (milimetr)
+margin-top =
+    .value = Brig:
+    .accesskey = B
+margin-top-invisible =
+    .value = Brig:
+margin-bottom =
+    .value = Gwaelod:
+    .accesskey = G
+margin-bottom-invisible =
+    .value = Gwaelod:
+margin-left =
+    .value = Chwith:
+    .accesskey = C
+margin-left-invisible =
+    .value = Chwith:
+margin-right =
+    .value = De:
+    .accesskey = D
+margin-right-invisible =
+    .value = De:
+header-footer-label =
+    .value = Penynnau a Throedynnau
+hf-left-label =
+    .value = Chwith:
+hf-center-label =
+    .value = Canoli:
+hf-right-label =
+    .value = De:
+header-left-tip =
+    .tooltiptext = Pennyn chwith
+header-center-tip =
+    .tooltiptext = Pennyn canol
+header-right-tip =
+    .tooltiptext = Pennyn de
+footer-left-tip =
+    .tooltiptext = Troedyn chwith
+footer-center-tip =
+    .tooltiptext = Troedyn canol
+footer-right-tip =
+    .tooltiptext = Troedyn de
+hf-blank =
+    .label = --gwag--
+hf-title =
+    .label = Teitl
+hf-url =
+    .label = URL
+hf-date-and-time =
+    .label = Dyddiad/Amser
+hf-page =
+    .label = Tudalen #
+hf-page-and-total =
+    .label = Tudalen # o #
+hf-custom =
+    .label = Cyfaddasu…
+print-preview-window =
+    .title = Rhagolwg Argraffu
+print-title =
+    .value = Teitl:
+print-preparing =
+    .value = Paratoi…
+print-progress =
+    .value = Cynnydd:
+print-window =
+    .title = Yn argraffu
+print-complete =
+    .value = Argraffu wedi ei Gwblhau.
+
+# Variables
+# $percent (integer) - Number of printed percentage
+print-percent =
+    .value = { $percent }%
+dialog-cancel-label = Diddymu
+dialog-close-label = Cau
diff --git a/thunderbird-l10n/cy/localization/cy/toolkit/printing/printPreview.ftl b/thunderbird-l10n/cy/localization/cy/toolkit/printing/printPreview.ftl
new file mode 100644
index 0000000000..31f01fb299
--- /dev/null
+++ b/thunderbird-l10n/cy/localization/cy/toolkit/printing/printPreview.ftl
@@ -0,0 +1,72 @@
+# This Source Code Form is subject to the terms of the Mozilla Public
+# License, v. 2.0. If a copy of the MPL was not distributed with this
+# file, You can obtain one at http://mozilla.org/MPL/2.0/.
+
+printpreview-simplify-page-checkbox =
+    .label = Symleiddio Tudalen
+    .accesskey = S
+    .tooltiptext = Nid oes modd symleiddio'r dudalen yn awtomatig
+printpreview-simplify-page-checkbox-enabled =
+    .label = { printpreview-simplify-page-checkbox.label }
+    .accesskey = { printpreview-simplify-page-checkbox.accesskey }
+    .tooltiptext = Newid cynllun ar gyfer darllen haws
+printpreview-close =
+    .label = Cau
+    .accesskey = C
+printpreview-portrait =
+    .label = Portread
+    .accesskey = o
+printpreview-landscape =
+    .label = Tirlun
+    .accesskey = l
+printpreview-scale =
+    .value = Graddfa:
+    .accesskey = G
+printpreview-shrink-to-fit =
+    .label = Lleihau i'r Maint
+printpreview-custom =
+    .label = Cyfaddasu…
+printpreview-print =
+    .label = Argraffu…
+    .accesskey = A
+printpreview-of =
+    .value = o
+printpreview-custom-scale-prompt-title = Graddfa Cyfaddasu
+printpreview-page-setup =
+    .label = Gosodiad Tudalen…
+    .accesskey = u
+printpreview-page =
+    .value = Tudalen:
+    .accesskey = a
+
+# Variables
+# $sheetNum (integer) - The current sheet number
+# $sheetCount (integer) - The total number of sheets to print
+printpreview-sheet-of-sheets = { $sheetNum } o { $sheetCount }
+
+## Variables
+## $percent (integer) - menuitem percent label
+## $arrow (String) - UTF-8 arrow character for navigation buttons
+
+printpreview-percentage-value =
+    .label = { $percent }%
+printpreview-homearrow =
+    .label = { $arrow }
+    .tooltiptext = Tudalen gyntaf
+printpreview-previousarrow =
+    .label = { $arrow }
+    .tooltiptext = Tudalen flaenorol
+printpreview-nextarrow =
+    .label = { $arrow }
+    .tooltiptext = Tudalen nesaf
+printpreview-endarrow =
+    .label = { $arrow }
+    .tooltiptext = Tudalen olaf
+printpreview-homearrow-button =
+    .title = Tudalen gyntaf
+printpreview-previousarrow-button =
+    .title = Tudalen flaenorol
+printpreview-nextarrow-button =
+    .title = Tudalen nesaf
+printpreview-endarrow-button =
+    .title = Tudalen olaf
diff --git a/thunderbird-l10n/cy/localization/cy/toolkit/printing/printUI.ftl b/thunderbird-l10n/cy/localization/cy/toolkit/printing/printUI.ftl
new file mode 100644
index 0000000000..3a44b29cff
--- /dev/null
+++ b/thunderbird-l10n/cy/localization/cy/toolkit/printing/printUI.ftl
@@ -0,0 +1,152 @@
+# This Source Code Form is subject to the terms of the Mozilla Public
+# License, v. 2.0. If a copy of the MPL was not distributed with this
+# file, You can obtain one at http://mozilla.org/MPL/2.0/.
+
+printui-title = Argraffu
+# Dialog title to prompt the user for a filename to save print to PDF.
+printui-save-to-pdf-title = Cadw Fel
+
+# Variables
+# $sheetCount (integer) - Number of paper sheets
+printui-sheets-count =
+    { $sheetCount ->
+        [zero] { $sheetCount } dalen o bapur
+        [one] { $sheetCount } dalen o bapur
+        [two] { $sheetCount } ddalen o bapur
+        [few] { $sheetCount } dalen o bapur
+        [many] { $sheetCount } dalen o bapur
+       *[other] { $sheetCount } dalen o bapur
+    }
+
+printui-page-range-all = Y Cyfan
+printui-page-range-current = Cyfredol
+printui-page-range-odd = Odrif
+printui-page-range-even = Eilrif
+printui-page-range-custom = Cyfaddas
+printui-page-range-label = Tudalen
+printui-page-range-picker =
+    .aria-label = Dewis yr ystod tudalen
+printui-page-custom-range-input =
+    .aria-label = Rhowch ystod tudalen cyfaddas
+    .placeholder = e.e. 2-6, 9, 12-16
+
+# Section title for the number of copies to print
+printui-copies-label = Copïau
+
+printui-orientation = Cyfeiriad
+printui-landscape = Tirlun
+printui-portrait = Portread
+
+# Section title for the printer or destination device to target
+printui-destination-label = Cyrchfan
+printui-destination-pdf-label = Cadw i PDF
+
+printui-more-settings = Rhagor o osodiadau
+printui-less-settings = Llai o osodiadau
+
+printui-paper-size-label = Maint papur
+
+# Section title (noun) for the print scaling options
+printui-scale = Graddfa
+printui-scale-fit-to-page-width = Yn ffitio i led y dudalen
+# Label for input control where user can set the scale percentage
+printui-scale-pcent = Graddfa
+
+# Section title (noun) for the two-sided print options
+printui-two-sided-printing = Argraffu dwy ochr
+printui-two-sided-printing-off = Diffodd
+# Flip the sheet as if it were bound along its long edge.
+printui-two-sided-printing-long-edge = Fflipio ar ymyl hir
+# Flip the sheet as if it were bound along its short edge.
+printui-two-sided-printing-short-edge = Fflipio ar ymyl fer
+
+# Section title for miscellaneous print options
+printui-options = Dewisiadau
+printui-headers-footers-checkbox = Argraffu penynnau a throedynnau
+printui-backgrounds-checkbox = Argraffu cefndiroedd
+
+## The "Format" section, select a version of the website to print. Radio
+## options to select between the original page, selected text only, or a version
+## where the page is processed with "Reader View".
+
+# The section title.
+printui-source-label = Fformat
+# Option for printing the original page.
+printui-source-radio = Gwreiddiol
+# Option for printing just the content a user selected prior to printing.
+printui-selection-radio = Dewis
+# Option for "simplifying" the page by printing the Reader View version.
+printui-simplify-page-radio = Symleiddiwyd
+
+##
+
+printui-color-mode-label = Modd lliw
+printui-color-mode-color = Lliw
+printui-color-mode-bw = Du a gwyn
+
+printui-margins = Ymylon
+printui-margins-default = Rhagosodiad
+printui-margins-min = Lleiafswm
+printui-margins-none = Dim
+printui-margins-custom-inches = Cyfaddas (modfeddi)
+printui-margins-custom-mm = Cyfaddas (mm)
+printui-margins-custom-top = Brig
+printui-margins-custom-top-inches = Brig (modfeddi)
+printui-margins-custom-top-mm = Brig (mm)
+printui-margins-custom-bottom = Gwaelod
+printui-margins-custom-bottom-inches = Gwaelod (modfeddi)
+printui-margins-custom-bottom-mm = Gwaelod (mm)
+printui-margins-custom-left = Chwith
+printui-margins-custom-left-inches = Chwith (modfeddi)
+printui-margins-custom-left-mm = Chwith (mm)
+printui-margins-custom-right = De
+printui-margins-custom-right-inches = De (modfeddi)
+printui-margins-custom-right-mm = De (mm)
+
+printui-system-dialog-link = Argraffu gan ddefnyddio deialog y system ...
+
+printui-primary-button = Argraffu
+printui-primary-button-save = Cadw
+printui-cancel-button = Diddymu
+printui-close-button = Cau
+
+printui-loading = Paratoi Rhagolwg
+
+# Reported by screen readers and other accessibility tools to indicate that
+# the print preview has focus.
+printui-preview-label =
+    .aria-label = Rhagolwg Argraffu
+
+printui-pages-per-sheet = Tudalennau fesul dalen
+
+# This is shown next to the Print button with an indefinite loading spinner
+# when the user prints a page and it is being sent to the printer.
+printui-print-progress-indicator = Argraffu…
+printui-print-progress-indicator-saving = Yn cadw…
+
+## Paper sizes that may be supported by the Save to PDF destination:
+
+printui-paper-a5 = A5
+printui-paper-a4 = A4
+printui-paper-a3 = A3
+printui-paper-a2 = A2
+printui-paper-a1 = A1
+printui-paper-a0 = A0
+printui-paper-b5 = B5
+printui-paper-b4 = B4
+printui-paper-jis-b5 = JIS-B5
+printui-paper-jis-b4 = JIS-B4
+printui-paper-letter = US Letter
+printui-paper-legal = US Legal
+printui-paper-tabloid = Tabloid
+
+## Error messages shown when a user has an invalid input
+
+printui-error-invalid-scale = Rhaid i'r raddfa fod yn rhif rhwng 10 a 200.
+printui-error-invalid-margin = Rhowch ymyl ddilys ar gyfer y maint papur a ddewiswyd.
+printui-error-invalid-copies = Rhaid i gopïau fod yn rhif rhwng 1 a 10000.
+
+# Variables
+# $numPages (integer) - Number of pages
+printui-error-invalid-range = Rhaid i'r raddfa fod yn rhif rhwng 10 a { $numPages }.
+printui-error-invalid-start-overflow = Rhaid i rif y dudalen “o” fod yn llai na rhif y dudalen “i”.
diff --git a/thunderbird-l10n/cy/localization/cy/toolkit/reportBrokenSite/reportBrokenSite.ftl b/thunderbird-l10n/cy/localization/cy/toolkit/reportBrokenSite/reportBrokenSite.ftl
new file mode 100644
index 0000000000..6fbe8159b2
--- /dev/null
+++ b/thunderbird-l10n/cy/localization/cy/toolkit/reportBrokenSite/reportBrokenSite.ftl
@@ -0,0 +1,3 @@
+# This Source Code Form is subject to the terms of the Mozilla Public
+# License, v. 2.0. If a copy of the MPL was not distributed with this
+# file, You can obtain one at http://mozilla.org/MPL/2.0/.
diff --git a/thunderbird-l10n/cy/localization/cy/toolkit/updates/backgroundupdate.ftl b/thunderbird-l10n/cy/localization/cy/toolkit/updates/backgroundupdate.ftl
new file mode 100644
index 0000000000..aee9a60f17
--- /dev/null
+++ b/thunderbird-l10n/cy/localization/cy/toolkit/updates/backgroundupdate.ftl
@@ -0,0 +1,5 @@
+# This Source Code Form is subject to the terms of the Mozilla Public
+# License, v. 2.0. If a copy of the MPL was not distributed with this
+# file, You can obtain one at http://mozilla.org/MPL/2.0/.
+
+backgroundupdate-task-description = Mae'r dasg Diweddariad Cefndir yn chwilio am ddiweddariadau i { -brand-short-name } pan nad yw { -brand-short-name } yn rhedeg. Mae'r dasg hon yn cael ei gosod yn awtomatig gan { -brand-short-name }, ac yn cael ei hailosod pan fydd { -brand-short-name } yn rhedeg. I analluogi'r dasg hon, diweddarwch osodiadau'r porwr neu'r gosodiad polisi menter { -brand-short-name } "BackgroundAppUpdate".
diff --git a/thunderbird-l10n/cy/localization/cy/toolkit/updates/elevation.ftl b/thunderbird-l10n/cy/localization/cy/toolkit/updates/elevation.ftl
new file mode 100644
index 0000000000..5c8dd3ab4c
--- /dev/null
+++ b/thunderbird-l10n/cy/localization/cy/toolkit/updates/elevation.ftl
@@ -0,0 +1,14 @@
+# This Source Code Form is subject to the terms of the Mozilla Public
+# License, v. 2.0. If a copy of the MPL was not distributed with this
+# file, You can obtain one at http://mozilla.org/MPL/2.0/.
+# This is temporary until bug 1521632 is fixed
+
+elevation-update-wizard =
+    .title = Diweddaru Meddalwedd
+elevation-details-link-label =
+    .value = Manylion
+elevation-error-manual = Gallwch ddiweddaru { -brand-short-name } gyda llaw drwy ymweld â'r dolenni a llwytho'r fersiwn diweddaraf:
+elevation-finished-page = Diweddariad yn Barod i'w Osod
+elevation-finished-background-page = Mae diweddariad diogelwch a sefydlogrwydd ar gyfer { -brand-short-name } wedi ei lwytho i lawr ac mae'n barod i'w osod.
+elevation-finished-background = Diweddaru:
+elevation-more-elevated = Mae'r diweddariad angen breintiau gweinyddwr. Bydd y diweddariad yn cael ei osod y tro nesaf y bydd { -brand-short-name } yn cychwyn. Mae modd ailgychwyn { -brand-short-name } nawr, parhau i weithio ac ailgychwyn yn hwyrach, neu wrthod y diweddariad.
diff --git a/thunderbird-l10n/cy/localization/cy/toolkit/updates/history.ftl b/thunderbird-l10n/cy/localization/cy/toolkit/updates/history.ftl
new file mode 100644
index 0000000000..4a4b6dcb09
--- /dev/null
+++ b/thunderbird-l10n/cy/localization/cy/toolkit/updates/history.ftl
@@ -0,0 +1,29 @@
+# This Source Code Form is subject to the terms of the Mozilla Public
+# License, v. 2.0. If a copy of the MPL was not distributed with this
+# file, You can obtain one at http://mozilla.org/MPL/2.0/.
+
+history-title = Hanes Diweddaru
+history-intro = Mae'r diweddariadau canlynol wedi eu gosod
+
+close-button-label =
+    .buttonlabelcancel = Cau
+    .title = Hanes Diweddaru
+
+no-updates-label = Dim diweddariadau wedi eu gosod eto
+name-header = Enw'r Diweddariad
+date-header = Dyddiad Gosod
+type-header = Math
+state-header = Sir/Talaith
+
+# Used to display update history
+#
+# Variables:
+#   $name (String): name of the update
+#   $buildID (String): build identifier from the local updates.xml
+update-full-build-name = { $name } ({ $buildID })
+
+update-details = Manylion
+
+update-installed-on = Gosodwyd ar: { $date }
+
+update-status = Statws: { $status }