My DH is autistic and when I met him he was fluent in Russian, Polish and German. He "got by" in French, Spanish, Swedish, Italian, Suomi, Mandarin, Arabic and Gaelic.
He also played piano at a concert level, and 8 other instruments but did not manage the well with the cello, fiddle, oboe or trumpet.
My pet theory is that he lives a binary life - things are either right or wrong. He works in finance - the sums at the end of the spread sheet are either right or there's a mistake to be found. That's why he liked the piano, the note is either right and in the right place or not. He wanted all the notes to be in the right place and kept practicing until they were. I THOUGHT he was expressing himself through music, but he wasn't seeing music in the way I was hearing it at all, for him it was a technical enterprise and he enjoys watching a orchestra jigsaw the notes together as a team - I'm probably expressing that clumsily.
Same with languages - his accent was "as good as a native speaker" or it was not, and so he kept going until it was. He lived and worked in Russia as a new graduate until he felt he "passed" as a native - then moved to Poland, then Germany, and I suspect he'd have kept travelling on only I met him and we settled down!
He says he's no longer fluent (it's 30 years since he lived in Russia) but he's handy for keeping up with the news from Ukraine as he still has an ear for a thick Russian accent.
He's the smartest person I've ever met - but is often totally bemusing/bemused as he can't "read" emotions as they are not binary, well, not in me.
I'm ADHD. It's not a boring marriage...