> That doesn't change the fact that during the critical period people are muuuuch better at acquiring language than after. I don't know about direct comparison

> That doesn't change the fact that during the critical period people are muuuuch better at acquiring language than after. I don't know about direct comparison of abilities of an adult and a child. The trouble is: child does nothing but learning, not just language, but he/she has a lot of daily practice. At the same time adult learning a language could spend a few hours per week learning, forgetting about the language at all other times. This difference itself might explain differences in outcome, there is no need to invent one more reason like "critical period" for the explanation. To learn language child needs ~3 years. Give me 3 years of learning language for 5 hours per day, I'll learn it no worse than a child or even better.