Hi Nant,
I've installed fr language plugin.
In the fr-fr folder, in the language.php file there is some strings like these ones :
DEFINE ('_UE_MONTHS_1','Janvier');
DEFINE ('_UE_MONTHS_2','Février');
DEFINE ('_UE_MONTHS_3','Mars');
DEFINE ('_UE_MONTHS_4','Avril');
DEFINE ('_UE_MONTHS_5','Mai');
DEFINE ('_UE_MONTHS_6','Juin');
DEFINE ('_UE_MONTHS_7','Juillet');
DEFINE ('_UE_MONTHS_8','Août');
DEFINE ('_UE_MONTHS_9','Septembre');
DEFINE ('_UE_MONTHS_10','Octobre');
DEFINE ('_UE_MONTHS_11','Novembre');
DEFINE ('_UE_MONTHS_12','Décembre');
Kind regards