XF 1.4 Language/Locale in addon.xml

Not sure if this is the right place to ask, but I'm currently developing an addon which uses template modifications.

Within this modification I would like to output the current language (best in form of a 5-digit locale) e.g.: en-US, de-DE, ...

How would I do that?

My workaround would be to add a phrase and translate it in every language, but that seems weird.

Maybe you also know how I can access values from the config.php file?