docs(locale): document fallback behavior for language_code property

discord/enums.py

@@ -772,6 +772,9 @@ class Locale(Enum):
     def language_code(self) -> str:
         """:class:`str`: Returns the locale's BCP 47 language code in the format of ``language-COUNTRY``.
 
+        This is derived from a predefined mapping based on Discord's supported locales.
+        If no mapping exists for the current locale, this returns the raw locale value as a fallback.
+
         .. versionadded:: 2.6
         """
         return _UNICODE_LANG_MAP.get(self.value, self.value)