Switching the language in Site Settings is not changing the UI language

[sleidig]

The app language is not easily changeable anymore.

To Reproduce
Steps to reproduce the behavior:

1. Go to Admin > Site Settings
2. Edit and change the "Default Language"
3. Save. The language is still the old one
4. Reload. The language is still the old one
5. Reset the app (from (i) icon bottom left). The language is still the old one

Expected behavior
The language should switch to the new one immediately after saving (?). If necessary, automatically reloading the app.

[sleidig]

While after initial setup we usually have config in one language that cannot easily be switched, the app language should still be changeable, I think.