K.,
You are right to be asking about this. The ability to communicate is crucial. Yes, those who do not become very good at it can still go to medical school, but who among us hasn't 'fired' a doctor because of crappy communication? No matter what journey your son takes in life, becoming expert in his communication skills will serve him well and make him much more successful than he otherwise would be.
First, envision your son all grown up, and a master at communicating. Use that vision to guide you as far as what he still needs to learn.
Start building this way:
1) pick a few things he wants every day, and is requesting without the correct word. For example, a cup. When he wants it, don't just give it to him when he grunts & reaches. Hold it, smile, say "cup! You want your cup?" He'll probably try to do what he has been doing so far, & reach & grunt some more. Pretend you don't understand.. & ask again, "cup?" If he gives you a response that is closer to the right word, then you give it to him.
If he is having success with this method, then this works, and he probably won't require more intensive work/treatment to progress. Just keep tabs on his progress. After he gets his objects down, start making him choose.. do you want the red cup or the blue cup? You can check his understanding of things like colors and numbers by asking him to bring you "2 shoes," or "go get the red ball." Then teach the things that he doesn't know yet.
2). Talk with him constantly. I gave my children a play-by-play on everything. (ie. We are walking to the cupboard, here is the handle, I am opening it up, here is the red cup, now let's close the cupboard. We are walking to the sink. Here is the sink and here is the faucet. I'm turning on the faucet, oh look! here is WATER! Let's fill the cup... up, up, up.. it's full! Now you can have your water in the red cup! Drink your water!
This was a lot of work, but I did it in a playful way.
The effect was that my children were way ahead of the curve in language. Did that make a difference? ABSOLUTELY!!!!
Others took them more seriously because they could interact and express themselves in a more intelligent manner. As a result, both children experienced themselves as "intelligent." This was very noticeable when they were young and people did not expect much from them. After the 'cute baby' remarks, people were surprised to receive eye contact and conversation from the 'cute baby.' As a result, instead of being treated like they were not there as a sentient being, they became part of the social exchange.
I have paid close attention to their language development. This was particularly helpful with my son. It turned out that language was actually very difficult for him. At one point, he was diagnosed LD because of the difference between his IQ and written language. (Should I have carried around a white board? haha BTW, we did read and read and read, that wasn't it). This difficulty did not impact his oral language, I think because of the rich environment I gave him. He never became so far behind that he had to have 'services,' and now in high school, he can still pull off a 'B,' even with the toughest English teacher. Because he can express himself well, I have to remind teachers that writing is more difficult. Otherwise they think the smart kid with the rich vocabulary is slacking.
So, please do work with your son, and make language a priority. We do know that the strongest predictor of success is not IQ, but social skill. Communication is at the heart of that. So, without worry but a sense of purpose, smile and talk with that boy all day long!