Robots Invent Their Own Language
discovermagazine.com
discovermagazine.com
As for whether they need sound-based languages, that's a good question. Presumably the folks developing AI would like to keep that AI at least somewhat anthropomorphized, so that we will always have a sense for what the robots are doing. It's much easier to interact with, and teach, a robot when we're capable of communicating with it on a common ground.
(Great movie, watch it: http://www.imdb.com/title/tt0064177/ )