$lang =& JFactory::getLanguage();
$locales = $lang->getLocale();
$locale = str_replace('-','_',substr($locales[0],0,5)); //This will get you "en_US" etc.

You can use this in Joomla extensions where you need to get the current language locale for example to use with Facebook Connect/Like plugins etc. in the "en_US" format. With facebooj JS, all you have to do is replace the default locale with the resulting variable something like this:

 e.src = document.location.protocol +'//connect.facebook.net/<?=$locale?>/all.js';

Get Joomla language locale for use with Facebook js/fbml etc. on multilingual sites

joomla, facebook

PHP