Xubuntu: Missing possibility to switch keyboard layout on desktop (live and installed)

In Xubuntu there is no option to switch between multiple keyboard layouts.
The only way to use an explicit keyboard is to only define that single keyboard laylout.
Recognized with Xubuntu 20.04 and 20.10 either with live system ("Try Xubuntu") or installed desktop.

The installed desktop already has the x11-xkb-utils and xfce4-xkb-plugin packages installed.

Reproduction:
* Boot Live CD, keep English and click "Try Xubuntu"
* Menu "Settings > Keyboard"
* Tab "Layout"
* Disable "Use System Defaults"
* Add "German (no dead keys)" and move it to the top

Now you have two keyboard layouts, but English is still enabled and not German (although German is placed before English), and there's no possibility to switch to the German keyboard layout.
Open Mousepad to verify that still the English QWERTY is active, instead of the German QWERTZ.

* Go again to "Settings > Keyboard", tab "Layout"
* Remove "English"

Open Mousepad once again to verify that now the German QWERTZ is enabled.