"Dych chi'n mynd i'r sinema?"
Translation:Are you going to the cinema?
Well, it should probably accept 'movie theater' but 'movies' is a bit different as it's referring to the films themselves and not the building and it's also a different register. In Welsh, you could talk about the sinema being demolished but in American English you wouldn't talk about the 'movies' being demolished (I don't think — not a speaker of American English).
I might say something like, i'r fflics or something for to the movies but that's both old fashioned and a bit Wenglish.
Thanks for the Welsh perspective.
FYI, you're right that one wouldn't say "the movies are being demolished." in America. However, the standard spoken expression here is indeed "I'm going to the movies." In contrast, "I'm going to the movie theater" sounds as though one is focusing on the physical location for some other reason than watching a movie (maybe to meet someone or to say where the fire happened). "I'm going to the cinema" sounds affectedly British. Oddly enough, the business showing the movies might well be called something like "Fourth Street Cinema" but that has no bearing on the colloquial spoken expression. "Film" is a tad pretentious, and "flicks" is self-consciously old-fashioned or slangy.
In the UK we don't say "movie theatre" the way Americans do. If we're going to see a play, that's at a theatre; if we're going to see a movie, we're going to the cinema. The exception would be if the premises showing a movie happened to be called a theatre: for example, the nearest place to us that shows movies is called "Strode Theatre" (and it also shows plays).