Hi François,
Unfortunately, the current spellcheck algorithm (SOUNDEX) is geared entirely towards the english language. It's performance in other languages would be quite poor.
You can experiment with it anyway, if you like - you'll need to rebuild the dictionary index file with a french word list, using the "build_dict.pl" perl script in admin/tools.
Jason Rhinelander
Gossamer Threads jason@gossamer-threads.com