I've seen many Chinese immigrants in Montreal whose English needs to get mended. But they put no efforts in it.

I'm afraid by that, they've drastically narrowed down their future career choices and flexibility.

Anyways, they made that choice. Who am I to insist they should enhance their English? Moreover, it's really very painstaking and time-consuming (been there, done that), as a matter of fact which most of native speakers of Western languages never have seemed to comprehend, by the way.