Huawei
Change the System Language auf Huawei
Huawei phones ask for a system language once, during the initial setup. That choice is not permanent. EMUI keeps a list of installed languages and always uses whichever one sits at the top of that list as the active system language.
If the language you want is not installed yet, EMUI treats it as unavailable, even if you select it briefly in a menu. Adding it first and then moving it to first place is what actually switches the interface, menus, and system apps over to the new language.
To change it, go to Open the settings ➔ Tap on System & updates ➔ Tap on Language & input ➔ Tap on Language and region. From there, either drag an already installed language to the top of the list, or tap add language if it is missing.
After picking the language via Choose a language, confirm the switch with Confirm with Change. The interface updates immediately, without a restart.
Keyboard languages and some third-party apps have their own language settings and may not follow the system change automatically. Check those separately if text input still shows the old language.