But I think the younger a person is, the easier it is to learn languages. We had some time ago when my nephew got married. Visit from his wife's girlfriend. They live in Sweden and both work at the university. He is Spanish, she is German and her little daughter, 6 years old, has no problems using several languages. She speaks German with mom, Spanish with dad, and since the parents don't speak each other's mother tongues so perfectly, they also talk in English. No problem for the no girl, who of course also has to speak Swedish in her kindergarten. The little one really impressed me.
One of my grandfathers was Swedish. If I had to try to speak Swedish, no one would understand me, because, like French, the "music" of the language is hard to imitate. I had a friend who studied Chinese. Chinese really is a set of separate languages, not "dialects". He was in an advanced class with a distinguished professor, who tried to teach in Mandarin, which wasn't his native "dialect". He was so bad, the students had to ask him to speak in English so they could understand him.
I worked with a woman from Hong Kong. We went out to a local Chinese restaurant for lunch. She starts ordering in Chinese, since the waitress is clearly a student from China. The waitress cuts her off, in English. "I'm sorry, I don't speak Cantonese."
I also have a couple of friends who were in the Peace Corps years ago in Ethiopia. In training, people had to speak in Amharic, and at dinner in particular for the first few days they had to point to things in order to eat. In Ethiopia, Susan came up to an old man to ask him a question in Amharic. He says, in Amharic, "I don't speak English." She says, in Amharic, "But I am speaking to you in Amharic."
Ira taught chemistry in Tigray, which was had as much trouble then as it does now. He eventually had to leave when the Army came in. But while he was there, he used a British textbook from about 1890 that said that the inert gases do not form compounds. In fact, there was what was then recent research indicating that they could. He told the kids the textbook was wrong about this. The principal called him in and said that one NEVER says the textbook is WRONG.
We really need Star Trek's "universal translator" so everybody hears everything in their preferred tongue.
I agree with you about kids. They haven't be socialized yet to feel shame for mistakes and suppress logic for social reasons. That's why it's so much fun to hear them question rules. "Why?". Another friend was at the zoo with his kids. The giraffe suddenly has a huge erection. "What's that?". The father says "nothing". His wife says "well he doesn't have an ego".