W.B.
Hi Y.,
My advice is going to be a little different....
I have a 6 y/o son and when he was 3 you couldn't understand anything he said. He stayed with Grandma and there was very little communication, interaction anyway. I was very concerned. Grandma didn't really puch the vocabulary and could understand his grunts and such. I didn't really care for it myself. Anyway when he was 3 I started staying home and watching other children in my home, within 6 months his talking was completely different, you could understand what he was saying and everything. By the time it had been a year you couldn't even tell there was a problem. I'm not saying that this is your case but sometimes children don't feel the need to use words and things because their needs are met by the sounds and noises the make.
Here is my suggestion....
When he wants something make him try to pronounce the word. Alos try something when he asks for something start telling him I don't understand that response, it is either yes or no, or whatever he is asking for. Start with little things and work up from there. I have watched some kids that would answer witj umm hmmm and uttt ummm, I don't understand those sounds and I would make them talk, sometimes it was just because the constantly had fingers in their mouth. One other thing you can do is get him into a play group, even going to the playland at McDonalds or like at the mall will work, this builds his vocabualary and communication skills. With siblings sometimes they speak their ow language and although you may not here it, they still communitcate with each other. This is not to say that you shouldn't take him to the Dr and have him checked out, because you should, but in the mean time start trying these things and see if they start to work. Hope this helps, W.