Why can't I change movie language?
When the movie is displayed it says: german, english, french. I pay 4.50 to rent it, and then it's only in german. My husband does not speak german, so I just paid 4.50 for nothing. this sucks.
Apple TV 4K, tvOS 16
In what country did you purchase this rental? What was the movie title?
The listed language support is separated for audio languages and subtitle languages. Those would often differ [e.g. more subtitle tracks than audio tracks]. Please be precise about what was listed.
When multiple languages are offered in a stream, then users can change that as described here: Change subtitles or languages for videos in the Apple TV app or iTunes Store - Apple Support. German may (or may not) be the default/primary audio language, but more may be available.
In some countries or regions, you may find some movies as multiple items in the Store, each item with different language support. Verify that you got the intended edition. If you got the wrong edition accidentally, then contact the staff to have it corrected.
Not all movies have the languages that you would like, so check the included language tracks on the Details page (scroll down to Languages) in the Apple TV app.
I pay 4.50 to rent it
Are you perhaps in Switzerland/using a Swiss Apple ID account? (Other countries seem to use x.99 prices more often, although pricing for each region is up to the supplying studio.)