Tried streaming the movie "Oppenheimer" last night and it came through in Spanish. My Roku player is set to English and all other streams come through correctly... in English. Even the Oppenheimer trailer is in English, but the movie itself is in Spanish.
It's frustrating that Roku only allows you to post your complaint and not contact them directly about a problem.
It would probably help to mention what channel/app this happened on. Justwatch lists it as available on several, but “The Roku Channel” is not one of them.
There is no FREE version of Oppenheimer available, at least the recent one with Christopher Nolan. It is available through Prime if you are a subscriber. Otherwise, it is Buy/Rent from several other services.
Roku is only responsible for The Roku Channel. All others are controlled by their developers/services. In the case of Prime, language selection is not fun. You have to up-arrow from the menu bar when you start playing, then choose Language.
https://www.amazon.com/gp/help/customer/display.html?nodeId=GQ4468BXX9PLQADD