Going to Grad School, which language/framework should I learn?
djb_hackernews: You shouldn't be thinking languages, you should be thinking concepts. Take a look at your course schedule, find books and papers on those topics and get cracking. 
Your software development skills will probably be superior, or at least way more than is needed for a grad program. If all you know is how to write code, you'll have a tough time expressing the concepts you are learning in the classroom.