I just ran into this, but NOT on Paramount+ or Star Trek! I wanted to watch the series "Sprung" on FreeVee. You can watch it either through Amazon Prime or Freevee (Amazon own Freevee). When I watch through Prime, no problem, but when I decided to try the Freevee app, it plays in German! The captions also default to German if they are on. Oddly, this is only my Ultra 4800. A Roku 4 does not have this problem.
Exact same thing happening on mine with TNG language defaulting to Deutsch. I have to change audio track to English every time for over a week now. I've tried everything you mentioned. No solution yet.
Deutsch is 1st Alphabetically on the drop down list of languages so something is causing the language to default to first language available every episode. Seems like a Paramount issue to me but either way Someone needs to fix this software bug either P+ or Roku. Very annoying
"Black Books" did the same thing! Just switched languages one day. I looked in settings and it says it's in English, but that is NOT what they are speaking.
I am having the same issue with Bosch and other shows. Very frustrating!
It's not just a Roku problem, as my Star Trek TNG and Voyager dvd's, play in English but when I try to back them up to my HDD, because DVD's will eventually De Laminate. They only dub in German.