[Quoth]

I may be misunderstanding about the English, and indeed it's state.
Nagaland.
Perhaps 90% speak English, though it's the official language. Perhaps they don't have it as a first language. Some African countries have English as an official language because of having very many different tribes / languages.

Also Malta has English as the Official Language. If the UK leave EU, then Ireland & Malta will still be using English. More people speak Polish and Chinese than Irish in Ireland.

Anyway my main point is that there is UK/British English, American English (but some groups in USA have quite different English) and then variations of English in other countries that may have mostly native English speakers.

If editing a British English author you'll manage best if your native English is the British kind and similarly for American. I'd be less confident editing Samuel Clemens or Asimov than any Brontë or John Wyndham.

I've known people from "British", Afrikaans and African backgrounds. Also Canadians, Australians and Americans. Also English, Northern Irish, Irish (Dublin and Rural), both kinds of Welsh and various kinds of Scottish. I've also known perfect speakers of English from Hong Kong (in late 1970s). I've known Germans, Dutch, Swedish, Czech and Slovak people that spoke perfectly good English.

I don't know anyone from India face to face, I was making assumptions based on Wiki research of Nagaland.