French language set up but still not working

Dear Support and dear WP users,
Could you please help me to use WP in French? I’ve already gone through all the steps here: http://codex.wordpress.org/Installing_WordPress_in_Your_Language ,and everything seems ok (.mo and .po files, language folder, define WPLANG etc). I can’t explain why both the admin and the site are still in English, except for the parts that I could translate myself like the titles in the sidebar.
My config : Mac OS X 10.5.8, Firefox 15.0.1 and occasionally Safari 5.0.6 (that I can’t upgrade anymore) in which I dowloaded WP 3.4.2, hosted by OVH.
It would be great if someone could reply, thanks in advance!