Translation:That cinema always offers good movies.
5. When the plural indefinite or partitive article is used with an adjective that precedes a noun, des changes to de.
Yeah, I can't imagine anybody saying a theatre "proposes" films, nor "suggests" nor "recommends" - unless it has some odd arrangement whereby it has a list of suggestions and the patrons vote on what it will show next. I do like "offers", and I'm glad Duolingo accepted "shows" just now. Could the francophones among us verify that this usage of "proposer" is colloquial French?
There must be any number of cinemas which have only one theater. But this sentence doesn't let you know one way or the other. "toujour de bon film" and "toujours de bons films" sound identical. Seems like this happens a lot. Curious that the French language doesn't require a distinction in such cases. -Or, am I missing something?
There is no "toujour". It is "toujours". In this context, it will be understood as "always". The movie theater/theatre always puts on (shows/presents) what.... "a good film", or "good films". Maybe it is a little confusing because of using "de" instead of "des". When there is an adjective before the noun, the "des" switches to "de" (as explained above).