Once FB ultimate installed, the language can not be changed back to French

Hi Guys !
Thanks for this plugin.
I was wondering why once the plugin Facebook Ultimate is installed, the default locale is English for some parts.
The back end is in French (default language) but the frontend (adminbar, search form, register form) is now in English and cannot be changed.

I am using WP 3.3.1 and Buddy 1.5.2

Any ideas ?