1 files changed, 48 insertions, 0 deletions
diff --git a/sphinx/builders/latex/util.py b/sphinx/builders/latex/util.py
new file mode 100644
index 0000000..01597f9
--- /dev/null
+++ b/sphinx/builders/latex/util.py
@@ -0,0 +1,48 @@
+"""Utilities for LaTeX builder."""
+
+from __future__ import annotations
+
+from docutils.writers.latex2e import Babel
+
+
+class ExtBabel(Babel):
+    cyrillic_languages = ('bulgarian', 'kazakh', 'mongolian', 'russian', 'ukrainian')
+
+    def __init__(self, language_code: str, use_polyglossia: bool = False) -> None:
+        self.language_code = language_code
+        self.use_polyglossia = use_polyglossia
+        self.supported = True
+        super().__init__(language_code)
+
+    def uses_cyrillic(self) -> bool:
+        return self.language in self.cyrillic_languages
+
+    def is_supported_language(self) -> bool:
+        return self.supported
+
+    def language_name(self, language_code: str) -> str:
+        language = super().language_name(language_code)
+        if language == 'ngerman' and self.use_polyglossia:
+            # polyglossia calls new orthography (Neue Rechtschreibung) as
+            # german (with new spelling option).
+            return 'german'
+        elif language:
+            return language
+        elif language_code.startswith('zh'):
+            return 'english'  # fallback to english (behaves like supported)
+        else:
+            self.supported = False
+            return 'english'  # fallback to english
+
+    def get_mainlanguage_options(self) -> str | None:
+        """Return options for polyglossia's ``\\setmainlanguage``."""
+        if self.use_polyglossia is False:
+            return None
+        elif self.language == 'german':
+            language = super().language_name(self.language_code)
+            if language == 'ngerman':
+                return 'spelling=new'
+            else:
+                return 'spelling=old'
+        else:
+            return None