Thank you Bram.
I'm afraid I'm totally idiot. I have done what you said and no progress...
It's really strange:
In "user interface", I do "Francais" and "Apply". No change,then I restart as I'm invited to do.
English spoken.
Then I redo "user interface" and "Dutch" (for example) "Apply". Then some words are in french...amazing, isn'it?
But when I restart, it returns in English, as usual...