"Who is the mayor of this city?"
Translation:Thị trưởng của thành phố này là ai?
Maybe correct, but not equally correct. I think "... là ai?" is much more natural than "ai là ...". I never heard the latest.
If I'm right, then I prefer the don't accept "ai là ...", so we have to learn to avoid it. In other words, we learn to think as a Vietnamese and don't do direct translation.