Theoretically It should be possible in modifying both these files:
Localization.text
Localization - Quest.text
The first line in Localization.txt is:
Key,Source,Context,Changes,English,French,German,Klingon,Spanish
and other lines look like this:
bedroll,blocks,Block,KgNone,Bedroll,Sac de couchage,Schlafsack,,Saco de dormir
which implies that new languages can be added in the first line with a simple ',WhateverLanguage' and then added to every other line after a new ','
But given that Localization.text alone has currently 4910 lines it would be a LOT of work for a single person.