Marc, bonjour! My high school and college French classes were a very long time ago, but at least I remember enough to know that in your note "bibliotheque" must mean the Library fonts!
But I'm not sure exactly what your situation is. It seems, from your note, that, after you installed Leopard:
-In Word and AppleWorks, you see fonts stored in all three Fonts folders: the user Fonts folder, the system Fonts folder, and the Library fonts folder
-In Apple applications like Mail and iCal, you see only the fonts in the system Fonts folder, but in some other Apple applications you see some, but not all, of the other fonts.
Is this accurate?
You mention the Information Systeme of Apple menu, but not Font Book. Have you checked the
status of these fonts in Font Book? (It's in your Applications folder)