Samsung
Change Default Keyboard Language auf Samsung
Samsung Keyboard treats the system language as the default input, no matter how many additional languages you install afterward. This is why the keyboard keeps reverting to the wrong language when you switch apps or restart your phone, even though a second language is already added.
The order of the installed keyboard languages controls which one loads first. The language at the top of the list becomes the default, and every language below it only appears as a switch option.
To change the default, open Settings ➔ General management ➔ Samsung Keyboard settings ➔ Languages and types. Open the menu inside this screen and tap Reorder. Drag the language you want as default to the first position in the list and confirm.
This only works if the language is already installed as a keyboard language. If it is missing, add it first under Languages and types before reordering.
Reordering affects only the keyboard input language, not the system display language. Changing the system display language is a separate setting that also affects menus, apps, and notifications, not just typing.