I see this problem on every video french forums.
Apparently, a same solution/process works for some people and does not for other people.
What’s working on my MAcBookPro Snow Léo FCP 7 is :
– enable “Français numérique” (“digital French” !!!) in the preference panel/language/méthode de saisie
– choose “Français numérique” in the top bar of the Finder : the little french flag, with “123” beneath it.
-In FCP open the “Tool” tab, then choose “Modèle de clavier par défaut – Français” (Default Keyboard layout – French”)
Voilà !