First, a short personal note to make you understand why this is important to me. To make a long story short, the son of a friend has some atypical form of autism and language troubles. And that kid matters a lot to me, so I want to become stronger in helping him, to be able to better interact with him and help him overcome his troubles.
But I don't know much about psychology. I'm a computer scientist, with a general background of maths and physics. I'm kind of a nerd, social skills aren't my strength. I did read some of the basic books advised on Less Wrong, like Cialdini, Wright or Wiseman, but those just give me a very small background on which to build.
And psychology in general, autism/language troubles in particular, are fields in which there is a lot of pseudo-science. I'm very sceptical of Freud and psychoanalysis, for example, which I consider (but maybe I am wrong?) to be more like alchemy than like chemistry. There are a lot of mysticism and sect-like gurus related to autism, too.
So I'm bit unsure on how from my position of having a general scientific and rationality background I can dive into a completely unrelated field. Research papers are probably above my current level in psychology, so I think books (textbooks or popular science) are the way to go. But how to find which books on the hundreds that were written on the topic I should buy and read? Books that are evidence-based science, not pseudo-science, I mean. What is a general method to select which books to start in a field you don't really know? I would welcome any advise from the community.
Disclaimer: this is a personal "call for help", but since I think the answers/advices may matter outside my own personal case, I hope you don't mind.
I'm very sorry to hear about your friend's son. For whatever it's worth, I think it's awesome you're taking the time to educate yourself in order to better help the child.
Do you have a name for his particular form of autism? You mention it is atypical, and the specific symptoms may be important.
Once you have the particular name, Google Scholar and the Journal of PLoS Medicine may be good places to begin your search. Do database searches for a review article on the particular form of autism.
Review articles are the best way to come up to speed on any given scientific subject. They also provide a massive list of resources for further study. Specifically, look for review articles published in the last few years. To ensure quality, they must be published in a peer-reviewed, academic journal. In this case, peer-review is your best defense against pseudo-science. The more prestigious the journal, the better. IIRC, Science and Nature are the top two of the life sciences.
If you can't find any review articles on his particular form of autism, try to get one on autism in general. Heck, maybe try to do that, anyway. Between those two papers, there should be a wealth of citations for further research. Best case scenario, they cite a recent textbook.
Another approach would be to speak with a professor from a university. An expert in the field, particularly with knowledge of the specific form of autism, would be the jackpot. You can check their CV for a list of published papers and chapters. If their work on the subject is reputable - e.g. published, peer-reviewed, highly cited, etc. - then they are more likely the be a genuine authority. He or she can more aptly answer your questions and point you in the right direction.