Well you could simply dub it into English and problem solved. However US movies are a success because they are dubbed into
multiple languages.
Do you speak...
Disney typically does 40+ languages.
https://www.hollywoodreporter.com/news/argo-django-unchained-inside-weird-427453
However even the language isn't enough to appeal to local audiences. Subtle changes in cultural settings are also made.
China simply hasn't made any movie that appeals to global audiences and so isn't going to go through the hassle of Internationalization.
Plus having mainly Chinese actors in some types of movies may have a lagging credibility issue. You are still seen as backwards and not inventors to most of the world. So having some futuristic Star Wars type movie with an all Chinese cast may look out of place.
Not yet. We are $9.5B so far this year. You are still #2...which considering your population advantage and "so-called" 400 million middle class is quite baffling.