There isn't any official confirmation. In the profile on David on CNN's The Next List (Seen at the bottom of this page http://www.spoilertv.com/2012/04/game-of-thrones-cnn-next-list-to-air.html) David and Dan mentioned that there are other languages in GRRMs world and that they are hoping David would create those as well. David later repeated that information in an interview on Stupid For Game of Thrones (
) but that was before they agreed about any details or signed any contracts or whatever. What has happened since then is not known since they are keeping a close lid on things for season 3. What we do know is that David has work on 5 episodes in the coming season and that in total the word count is greater than it was in season 2. So the question is whether we believe that is just Dothraki work or whether it's more likely that it also means work on some other language.