Thanks, GAGL, for your usual thoughtful and well-researched response. I, too, admire your use of the Cyrillic alphabet (which, by the way, I can read).
Being that both spellings seem to have equal weight, and it is a foreign currency name translated from another language (particularly using a different alphabet), perhaps designating them both as rare might be a fair solution. I don't know, then, if there are other similar examples since it's a peculiar situation, but a uniform solution might be applied if they come up later.
