The series has now started and new dothraki words are coming out in nearly every episode. We are also learning more and more grammar and soon enough we will have a fairly learnable language. To follow the development on this site you can visit the forum (forum.dothraki.org) where all new information is first posted. Then things slowly but surely move into the wiki that is under constant development.
For people who are intersted in learning the language we are beginning to build a starting platform in the wiki at http://wiki.dothraki.org/dothraki/Learningdothraki.