I'd like to see their working for that number. Let's say we subtract 20% from Canada + the UK + the US, we get ~320 million. add Nigeria and Uganda and you have easily 400 million. That's without Australia, Ireland, New Zealand or any of the African or Caribbean countries.

> You have easily 400 million

No you don’t: https://en.wikipedia.org/wiki/Languages_of_Nigeria

~60 million people in Nigeria speak English out of 230 million people, but that 60 million isn’t almost exclusively native speakers.

There aren't that many native English speakers in Nigeria and Uganda. To me, it looks like your back-of-the-envelope calculation will come pretty close to 400 million.