It's needed in such sentences which show amazement, or surprise, also questions.
Co to był za mecz! = What a game that was!
Co to za butelka? = What (kind of) bottle is that? (Why is it here?)
A co to za wygłupy?! = What is this fooling around?!
(just some quick examples as I'm kinda in a hurry)
Immery (I think) made a comment on a similar statement, explaining that without 'za' it would be more like "what (is) a strange question" - the "what" being more literal and not an expression of surprise.
Well: Co to (jest) "butelka"? would be a question for the definition of the word 'butelka'.
I'd propose "Such a strange question!" as a valid, common, English expression.