Very familiar topic

I know 5 or 6 languages but I hang up talking or struggle to speak at all.
What helped encourage interactive communication?
It's hard to compare an adult to a child. For me, I feel overwhelmed, overstimulated, bright lights, background noise, all that keeps my wheels spinning that could be devoted to having the conversation. Overstimulation is a state of too much sensory input. Bright and/or flickering lights, noise, uncomfortable clothes, being touched, smells etc. Also poor sleep, lack of physical acrivity, dehydration, hunger, lack of breaks - they contribute to the feeling. Especially hard to get those physiological needs met when being autistic and having alexythymia. Routine helps. Even if you don't feel like it, take a 10-minute break every hour or so and drink, go to the bathroom, have a snack. Crowds or many people in one room indoors are overstimulating, so it's better to avoid those. Talk to people 1 on 1 or in small groups. Online shopping or activities are a less stimulating alternative. Some autistic people work online and like it better, but I prefer to see people. I don't work on site 40 hours a week but enough to have face to face contact, perhaps half of the 40 hours.
The second issue is that sensory issues, for me personally, make it harder to interact with others than for an average person, I have bad hearing because of autism filtering of the sensory input - there is noise that isn't filtered out and human speech sounds unclear. I can hear very quiet soudns very clearly, they're "zoomed in", but people - uh.... it takes effort to understand. Similarly I pick up on body language, but can't always see the facial expression, because the shadows and light make it blurry. - The solution to this problem is to make sure you're being heard and seen (gotta love the people who I never know tried to interact with me and claim to be ignored) and give the autistic person the time to form and articulate a response, it is harder for us and for a lot of us it takes more time.
That was my perspective. Recently a few people remarked that
1. They have no clue if I even hear them and I have to confirm somehow, say "aha" or if I don't feel like articulating even that then nod. Apparently autistics don't make faces and neurotypical people do as a part of communication. For sure it is different for different people, but I don't think I'm aware of making faces on purpose. I make a face when it's instinctual and it expresses a feeling without concious effort. So I wasn't aware that I'm being perceived as "no clue if he hears me or not" or as ignoring, you can't suddenly get a different brain and see things like others do. I didn't know about the facial expressions or that it matters and anyone pays attention. I saw that others come up with sophisticated verbal responses (not monosyllables) and I try to do the same, but I fail, because before I speak someome already interrupts me, because I'm too slow. ... So the takeaway is that your son might have a completely different perception of the situation and have no idea what you want from him. I have felt this way a number of times, but nobody explained for nearly 30 years. Except for criticism that I don't do enough of x or y, especially that I should speak in more complex sentences or "be confident" (no clue what it's supposed to mean in practice, because clearly not feeling confident, because I heard this even when feeling relaxed and confident). I would avoid abstract feeling names "be more [feeling]", and be more specific instead about behaviours and body language. Another takeaway is that an autistic person might find a "standard response" like a fast reciprocal complex verbal response to small talk too hard and impossible to do, so might never be "back and forth" the same way as neurotypical people. Another takeaway is that it doesn't mean they don't understand or don't empathise, but communication of autistic people is different, because our sensory perception is different often to the degree that humans are hard to comprehend and communication is so ineffective we get conditioned to be loners, there is no positive reinforcement in e.g. seeking to play with others as a child. I was a speaking child, but I remember trying to play with children as inaccessible, because I didn't hear well, and therefore it was no fun and I didn't get what the children said or did often. Blocks were fun.
2. The second remark was that I don't talk and hide in the corner while I didn't perceive it this way. It was explained to me that I'm supposed to talk about obvious things even if I personally don't find the interesting to share. That this kind of thing builds relationships. I don't perceive it this way and I don't think you have to talk a lot to be a friend or talk at all, in my opinion, hanging out is fine. I didn't realise there is anything any different about me in that regard. Again the same takeaway: an autistic person might have a differrnt opinion on communication, a different perception of it, and you might need to explain and be specific, because again, throwing around statements such as "be more open" doesn't explain much.
when it comes to communicating needs, emotions,
There is also the issue that he might not know what he is feeling or needs. Alexythymia is very common with autism, it is the inability to read your internal states such as feelings, physiological needs such as pain or hunger... A child might need help learning to recognise what they feel and what cues to look for.