Not sure why it wouldn't work but you can force it by editing the
more_share_tng template.
Find the line:
Code:
e.src = document.location.protocol + '//connect.facebook.net/{vb:rawphrase facebook_language}/all.js';
and change it to
Code:
e.src = document.location.protocol + '//connect.facebook.net/de_DE/all.js';
This mod can't be moved below the first post it is currently coded.