I'm working now on multi-lingual website with facebook like box module on frontpage. After testing multiple free modules BT Facebook Likebox. It's responsive and simple. The only problem was how to display module in current website's content language (Polish, Spanish and English). I've managed this with few clicks.

All changes are in file "modules\mod_bt_facebooklikebox\tmpl\default.php". You can create template override for this file by copying it into "\templates\your_template\html\mod_bt_facebooklikebox\" folder and edit this file.

First I have defined variable for getting language  code, right  after:

 defined('_JEXEC') or die('Restricted access');

I have added this:

 $lang = JFactory::getLanguage();

Next I have changed this:

 $href = 'http://www.facebook.com/plugins/likebox.php?href=';

into this:

 $href = 'http://www.facebook.com/plugins/likebox.php?locale='.str_replace("-","_",$lang-getTag()).'href=';

After this operations I have FB Likebox displayed in current website's content language.