Rajneesh,
JFBConnect will use whatever the current language of your Joomla site is, if you haven't specified an Locale Override, like we mentioned above. Are you currently using the override setting? If so, that will always force the language to whatever you set there. If you're not using that, how are you setting the language for the user automatically if they haven't already logged in yet? Does that work properly for the rest of your site now? If a user in France visits the site, is it automatically in French?
I'll need a bit more information on how you're auto-switching languages before we can understand how to get the FB language to switch properly if it isn't already. It should, but not sure why it isn't.
Thanks,
Alex