I have to recognition the net browser's listing of language preferences. Supported languages are British and French. For instance: http_accept_language="jp-JPfren-USen" redirects to some directory known as /French/. How do i do that with rewrite rules during my .htaccess file?

I wouldn’t use mod_rewrite with this but a far more effective language. Because Accept-Language is a listing of weighted values (see quality) and the appearance of among the identifiers does not necessarily mean that it is preferred over another value (especially q=0 means not acceptable whatsoever).

As already stated, make use of a more effective language than mod_rewrite, parse their email list of worth and get the best match of preferred options and available alternatives.