Unabbreviates language codes in BlacklightHelper.

Hey @annakrohn, was browsing through some of the catalog's code and found your comment in the BlacklightHelper - this commit could help.
I'd provide unit tests, but can't get the bundle installed, whether I try it with ruby 1.8.7, 1.9, 2.0 or 2.1. What version are you using?
That's also the reason why this may not work out of the box, not sure what values are provided in the value param, as I can't debug it due to the above mentioned reason.

Feel free to trash this PR without warning, in case you don't need it!