If you want FB Connect to render in other languages, you need to modify the plugins somewhat. The plugins are not built for internationalization yet.
Most of the text in the plugin is just hard coded. Just change it as you like.
The Facebook Connect buttons can be changed in languages by modifying the script calls. In the base plugin (sfc.php), you'll find this code:
wp_enqueue_script( 'fb-featureloader', 'http://static.ak.connect.facebook.com/js/api_lib/v0.4/FeatureLoader.js.php', array(), '0.4', false);
Change that to this:
wp_enqueue_script( 'fb-featureloader', 'http://static.ak.connect.facebook.com/js/api_lib/v0.4/FeatureLoader.js.php/fr_FR', array(), '0.4', false);
Voila, French. The different locales you can use are here: http://wiki.developers.facebook.com/index.php/Facebook_Locales
I can't help you with the contents of the popup. Facebook creates those, not the plugin.