Android
Change System Language auf Android
Android stores every installed language in one ordered list. The entry at the very top becomes the active system language, while the others stay available as fallback options for apps that only support certain translations.
To change the active language, open Tap on Settings ➔ Tap on System ➔ Tap on Languages ➔ Tap on System Languages. Here you see every language already installed on the phone.
To add a new one, tap Tap on Add a language and confirm with Select a Language. The new entry appears at the bottom of the list first, which means it has no effect yet.
Drag the language to the first position to set it as default, then confirm with Tap on Change. The interface, keyboard suggestions and system messages switch immediately.
If an app still displays the old language afterwards, it may only support the languages further down your list, or it uses its own language setting instead of the system default. Removing a language from the list only hides it from the fallback order and does not affect saved contacts, messages or files.