Cine is really cinema (accepted translation here for example) or if you prefer movie theater. So wrong to translate it as the movie (or film as we say in the UK! La pelicula in Spanish btw) Duo is accepting movies not as the plural of a single movie but as a "down with da kids" equivalent of cinema.
It's not an idiom, it's not slang, and it's not new. "The movies" meaning "the movie theater" has been in use since I was a child in the 1970s, perhaps for longer. Remember, Duolingo is an American company, so of course it defaults to American English. It also accepts phrasing from different dialects, but the course contributors can't be expected to know all of them. If enough people report that their translation should be accepted, the course contributors will add that version to the prompt's answer database.
This is clearly a new idiom and not a translation from literal Spanish. If this is actually how a Spanish speaker would phrase going to movies or a movie, DUO should clarify and introduce this with other idioms and not equate the word "cine" to movie or movies when it actually refers to a PLACE where movies may be viewed. Unfortunately, in English, we idiomatically speak of going to a movie when we mean going to a movie theater. With conflicting idioms, confusion reigns....
Of course "cine" means "cinema" (the place where fims/movies are shown), and this is exactly how it is introduced at Duolingo. The "problem" is only caused by the English language (at least the American variant) where it is idiomatic to talk about "the movies" when the place is meant.
I'm not fluent so it would be nice to get conformation of this from a native Spanish speaker. I believe 'cine' in this case is used like a plural/collective noun (like moose). When referring to one movie 'película' would be used. That said 'cines' is a word though I believe it is usually used to refer to multiple buildings where movies are shown and not multiple movies. Multiple movies would be either las películas o el cine.
I think that we're going through a beta-testing phase with the new changes to Duolingo. The range of accepted answers on quite a few new questions is too narrow. But Duolingo does make changes in response to reports, so the system is improving. It has given me some replies saying my rejected answer would now be accepted. Reporting helps us all.
Well, "movie theatre" is a strange mixture, because "theatre" is the British way of writing "theater" (American English), but only Americans call a cinema "movie theater". So "movie theater" might be accepted, but I'm not sure if it is at the moment. Next time try "movie theater", and, if it's not accepted, report it.
It's very rare for someone to say in English; let's go to the movie theater. Furthermore, in English there's a very subtle difference between go to the movie and go to the movies. In general if I use movies it means we haven't chosen a movie. Movie means we know which one we want to see.
"Cine" is always singular. It means "movie theater" or "cinema".
"Cines" is always plural. It means "movie theaters" or "cinemas".
But there are dialects of English that refer to that same place in the singular as "the movies". This is not the same as "película" or "películas", which is the actual movie or movies that you are sitting down to watch in the dark with popcorn.
When do you go?
When do you want to go?
¿Cuándo quieres ir?