I didn't talk until I was 4. I was able to say numbers, letters, and certain words at 2, but wasn't able to put together sentences until 4. My mom would take me to speech therapy from 1-4 years old, but it only helped marginally. I was socially awkward and very introverted for most of my childhood but went through some serious social skill learning when I was about 12-13, which helped tremendously.
The best thing to do with your son is just to wait for the language skills to grow. Just like is not going grow to be 6' tall overnight, he's not going to start talking immediately. I recommend showing him lots of love talking to him all of the time. Whenever you're with him, just babble on to him, without expecting a response. Talk to your son the same way you would to a pet until he can talk back.
I'm not sure which languages you want him to learn but whichever ones they are, he should be able to, fluently. People with autism don't have trouble learning foreign languages and translated words, it's more the basic ideas of language and especially non-verbal communication that are a struggle. If he grows up to be high-functioning, he will surely be able to hold a conversation in any language you teach him. I myself am fluent in 2 languages and learning another one.
If you can afford to send him to some kind of alternative school, I highly recommend it. Public schools in America are hell for people with AS. I went to a therapeutic school at a hospital for 8th grade and grew infinitely more as a person than I did in all of my other 11 years of public schooling combined. Therapeutic or art schools are the best.
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"Psychic kids, try to understand who made them this way, so they don't feel bad...floating in space, the ghost is out there, so you're not alone, only out there"
Sagittarius, ISFP, diagnosed with AS when I was 13.
http://www.last.fm/user/DolphinCove