Reproduced on http://demo.moodle.net/

If you go in any activity settings and find the calendar icon (the forum for example, Rating section), if you switch to French language and click the calendar icon, the weekday label gets dupplicate. As per admin settings, the week should aslo start on sunday (dimanche) and not on monday (lundi). I guess the two bug are related in some way, so I won't create a new one for this last issue.

Others non-english languages don't seem to have this problem.