On the moodle.org site, if I configure my user profile with French (Français) as my preferred language, the Moodle interface is displayed in French (block titles, etc.). However, none of the dates (in the calendar, in the dates of the forum discussions, etc.) is in French: they all remain in English.
The problem is particularly visible in the Français course, which most users would be browsing in French, of course.
Joseph
See this discussion: http://moodle.org/mod/forum/discuss.php?d=58663