1) does it all work in English?
2) are you sure you have refreshed the file languages/fr/acp/modes/sudoku.php?
3) does common sudoku game work in French?
i can't work on that right now because i'm far away from the civilization via GPRS modem but in a couple of days...

the same problem was in German at first---the code was perfect but the language file can't be opened in some servers