"Last night we watched a movie."
Translation:Anoche miramos una película.
According to my in-laws in Argentina it is "vemos una pelicula." But there is no consensus. It depends where you are.
Digging deeper because we know that language can commonly be misused, I found this: Ver significa: percibir una persona, animal o cosa por la vista.
Mirar significa: fijar o dirigir la vista con atención.
Ver means to perceive and mirar means to direct your visual attention to. We have the same distinction in to look at (ver) and to see (mirar).
Then, to watch a movie you probably pay attention to it so mirar una pelicula. And both are acceptable depending on where you are and local usage.