I know a few people who were born deaf, and have been raised in "Deaf Culture" - They are intelligent and erudite, and in one case an immensely gifted artist, but their writing is poor and difficult to understand by hearing-standard English speakers.

It turns out ESL is very, very, very different from spoken English, and the rules of grammar only really make sense to most people if they can "hear" them, either through language or sign - so ESL-native speakers come across as semi-fluent to us, and we to them, despite both of us claiming to write in English!