Hello! I have a vhshare site translated in french. I like my site but in some sections the text with accents does not appear correctly.

Exemple : the word Privée appear like that : Priv?e

I have this problem in almost all sections except video description text and channels details.
to divert the problem I am obliged to write texte without accents, butthe users who want to write comments don't know this problem and finally their text was not correct.

Is it a database problem, or may i modify some tpl files? And if this is the case? Which?
Thanks a lot.
ps : excuse my poor english, you know, i'm french ;-)