That's just a normal topic aimed to Vietnamese people. The language is still English, so I guess there is nothing wrong about this. There would probably be an issue if they were posting in their local language.
BTW wonder know why the locked Vietnamese topic is still sticky from 2017.
All official "local topics" are sticky.
There was this local topic for Vietnamese people, but due to spam, he locked it. Since that was the "Vietnamese local board", there is no place for them to post in their language.