I wondered about that when I was in college. Had a fellow student who was from China and had pretty poor spoken skills, but I had to write something (I think it was a write-up of a circuit) with him (on an old Mac SE/30) and his written English was amazing. It was such a weird split and not that uncommon or confined to the Chinese as I later found out.

I think it comes down to reading a lot and absorbing that formalism, but not really speaking that way because, well, spoken English is a different bird.