curiousHow common is it for someone in Russia to refer to a very close friend as "sister" or "brother"? I know that in Asian cultures, this occurs far more often than not, but I'm not clear if the same thing happens in Russian culture.
Context is a letter being written to someone else. The letter is most likely written during the 1970's-1980's (maybe a bit earlier, but definitely around the Cold War era), and it's been found by a journalist in present day. The letter is addressed to "my brother", and I need to know if it can be safely assumed that the two people really are siblings, or if there's a possibility that they're just close friends.
(It'll also be really helpful if someone can let me know that, if they can be just friends, exactly how close would they have to be for terms like "brother" and "sister" to be used?)
Thanks in advance!
