It’s working as expected. The half translations issue is likely due to either the Turkish translations being incomplete, or that we haven’t pulled them into the app build. Using a different language in Damus from your general iOS language preference is already supported out of the box by Apple.

iOS Settings > General > Language & Region. Ensure that English is also a preferred language, but it doesn’t necessarily have to be listed as the first one.

Then,
iOS Settings > Damus > Preferred Language > English.