You can put this sentence in two ways to express it as a question:
bạn là người Việt Nam? with intonation at the end just like some other languages, or you will be able to tell base on the scenario.
bạn là người Việt Nam phải không? in which "phải không" at the end indicates a question. This is also introduced in the course.
"You are Russian?" is a perfectly proper question in English, though it may be confusing, if the intonation is unclear. Like V. Ivanov, I'm quite surprised that tone can be used to indicate a question in a tonal language. I don't think it's possible in Chinese, for instance.
Hm, I think this question is simply wrong. If I say "Bạn là người Việt Nam?" than Vietnamese would understand: "You are Vietnamese!". Correct it should be "Bạn là người Việt Nam không?". since the Vietnamese intonate the words and not intonate the whole sentence like we Westerner it do, if we ask questions.