How to set the primary language for TMDB-data

I generally use both Trakt and TMDB, but as a German user I am actually quite happy that it is possible, at least in the context of apps, to use Trakt’s service in German using TMDB’s data.
I realize that I can change the language of the description for a single show or movie - but how can I set German, for example, as the primary language for the TMDB data fetched by the app? For example, when I open the profile of an actress, I always get it in English, even though the biography is available in German at TMDB.
How I can set the alternate language I realized - but for the primary language it is unclear to me.
A bit of a curious dilemma, as I have the exact opposite problem with my app for movies (“Movie Mate”). There, the overview shows everything in English TMDB data, but the data for movies and actresses are in German. This confuses me.
Thanks for the great work and your support. Stay healthy!

Thanks for reporting! Funny enough, the language is fixed to US English and there was never a setting for this.