Your additional couple of notes increases the probability that your son is displaying a developmental disorder manifested by more than just the language problem. It would be helpful to have him evaluated by a developmental pediatrician or, better yet, a team of developmental specialists.
Our son displays symptoms of SI. In response to the biting of himself, I attended a workshop and learned of a great strategy. Go to a pet store and buy a package of fish tank tubing. The one used when using a pump in the tank. At the fabric store, buy some decorative chord. Fish the chord through the tube (measure his wrist first) and then tie the "bracelet" around his wrist. When our son felt the need to bite something, he would chew on this tubing around his wrist. The good part of it was that no one else puts their mouth on this. He had strep throat for six months because he was constantly putting his mouth where others have touched. This eleviated many more throat infections.