Switch language within the app

But one thing they noticed is that we can't select language after the app's been installed

Current behavior is that the default system language will be used (if not available, whatever is closeby (es when choosing es_CU for example), then according to the priority if that also fails using the source language: en_US. Nowadays you can change per app the language, see https://developer.android.com/guide/topics/resources/app-languages

This is a user request. I'm not sure what priority this should be given.