I teach English as a second language to mainly middle-aged european business people, nearly all spoken/listening. There are I believe about 180 million Europeans who have English but are non-native speakers. I don't find the concept of "proper English" helpful in the least

Whatever, but if you speak English with a fat Scottish accent, I’m afraid our conversation will be short.

one of their biggest problems is occasionally coming across native UK English speakers who "speak proper" and think that's enough, and it's not their problem that people don't understand them and are shy or afraid to reply in case they make a Grammer/vocabulary error