A couple of points about this script:
* It's not a full translation of Facebook into your language but aims to deal with the most common things you see on screen when using Facebook
* You need Firefox or Chrome
* You must have Facebook set to Français (France).
If you're using Firefox
1) You will need a little program called Greasemonkey - this adds a bit of extra power to Firefox to handle the script.
2) Once you've installed Greasemonkey, click the green button at the top right which says "Install". You'll get a window which says "Greasemonkey Installation". Agree to the installation and that's it. You may have to restart Firefox. If you're still not seeing your language, check if Greasemonkey is "On" (it's possible to switch it "Off"). Look for the small monkey head on your Firefox bar - if it's really colourful, it's "On". If it's kind of greyed out, it's "Off" - click on it once to put it "On". That should do it!
If you have Google Chrome
1) Click the green button at the top right which says "Install". Agree to the installation and that's it. You may have to restart Chrome.
If there's any problems, give us a shout!