Wordpress : qTranslate X language switcher with language code

I'm trying to make a basic language switcher with qTranslate X, something like :

FR | EN

There's a function to achieve that : qtranxf_generateLanguageSelectCode('text'); but it can only accept 'text', 'image' or 'both', so it doesn't fit to my needs : 'text' is the full name of the language.

How can I just show the language code ? Any idea to make a filter to do that ?