Not sure if it is helpful but I have a friend whose son didn't talk until 5. One morning at breakfast he just came out with- "you know what mum, I really don't like vegemite toast. Can I please have cornflakes instead?" When asked why he hadn't spoken before hand, he said he didn't have anything to say. He went on to be the dux of his school.

Re sign language, it has helped some friends with late speakers and others it hasn't. I guess it is a case by case basis.

Fingers crossed everything works out for the best.