for English speakers, the literal translation of “нифига себе” appears as “по-фига to-yourself” instead of being completely in English.
фига is a kind of (sometimes) rude hand signal that we don’t have in western-European societies. So it doesn’t translate properly which is why it would have been left like that.
I beg to differ. I haven’t seen this in decades, but it was very “popular” here in Germany when I was in my teens (mind me, that was 30-40 years ago).
I wouldn’t have a clue about Germany, I’m from Australia and we don’t use it here. I listed the wikipedia article which is the authority on the subject not me.
I wouldn’t translate wow as нифига себе, though a lot depends on context: it could be OK in a conversation with your friend, but in other cases it may be not. The main difference between wow and нифига себе is that the latter is not just an exclamation, but it’s formed from фига which is a half obscene word and very often фигня is used as an euphemism to х…ня. In dictionaries it is marked as colloquial, vulgar and nonstandard. In my view Ничего себе! or Ух ты! are more adequate translations.