In mac OS X, it's possible to set different languages for every applications.
Select your Final Cut Pro application and hit command-i (Get Info). You can safely unchecked "french" in the Language section of the Get Info window. Don't click "Delete" unless you want to permanently remove the language from your HD.
This way, you could have Mac OS X in Spanich and FCP in english. I use this feature because i like to have Mac OS X in french, but I prefer some of my applications to stay in english.
I hope this will help you...