I don't see anything wrong with a question asking whether a particular work has ever been translated to a particular language.
First off, such questions are likely to be of practical use. Like identification questions and reading-order questions, they might actually help someone with a real problem, as well as just satisfying idle curiosity. To take your example, I'm interested in the Witcher series but am not fluent in Polish, so whether it's been translated into English is a fairly important question for me.
As b_jonas notes in comments, these questions have lasting value: if there is an existing translation, it won't suddenly disappear, and if there isn't, that answer will stand until someone creates one (which isn't likely to happen overnight). Stack Exchange fields questions about much more rapidly changing things than this on the various software-related sites.
They can also add to one's appreciation of a work. If a book written in French which is well-known in France has never been translated to English, there's likely to be an interesting reason for that. (I've heard of some examples of this kind of thing happening, for various reasons relating to the work itself and possibly political in nature, but I can't remember any offhand.)