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.
There is an ancient and noble tradition of burning a straw-Freud, which started during the Freudian analysis vs Jungian analysis and analysis vs behaviorism conflicts decades ago, and it is still used today to signal your allegiance to a specific tribe, usually either skeptical or religious, depending on context. On LW this tradition is honored during the winter solstice, too.
I would recommend against classical Freudian psychoanalysis in this case simply because it was developed for dealing with stuff like this, which is fairly uncommon in our society; and is probably completely unrelated to autism.
I'm sorry I can't give you a more specific advice than this: try to contact families with similar problems and ask what worked for them. Seems to me that no therapy is scientifically proved yet, but I would probably bet on something like CBT.
When dealing with an autistic child, my impression from reading some blogs is that you should not expect any "common sense" at people-related things. Just accept that the autistic child has greater inferetial distances and problem understanding metaphors, therefore explain to them everything very simply and literally.
I assume by "scientifically proved" you mean well supported by the available evidence, in which case CBT has already attained that [edit: I don't mean specifically for autism; Villiam_Bur's comment leads me to infer that he's referring to CBT being a potentially useful therapy more generally]. And the reason Freud is so disparaged is because his methodology was at best proto-scientific and at worst speculation, and yet people still take him seriously. For that reason, I speculate the hostility ostensibly directed towards Freud is actually intended for his current supporters.