Source

beamer / base / translator / dicts / translator-months-dictionary / translator-months-dictionary-French.dict

Diff from to

File base/translator/dicts/translator-months-dictionary/translator-months-dictionary-French.dict

 \providetranslation{September}{Septembre}
 \providetranslation{October}{Octobre}
 \providetranslation{November}{Novembre}
-\providetranslation{December}{Decembre}
+\providetranslation{December}{D\'ecembre}