It just occurred to me, when film or TV content is being dubbed, and they need a crowd shouting in the target language, what do they do? My guess is that there are places that specialize in recording "crowds chanting stuff" etc, and everybody sends that work to them.

I imagine they use the same stock sounds that their local theaters do when a scene is taking place in a supposedly crowded room. Sound engineers: I don't know exactly what they do but is probably pretty cool.