Change to a Customize language will not be used after restart

Question

Hi,

I have created a custom language (German - since the built-in one is not fully translated). I can also set this language under "Languages" ➜ "Custom language" ➜ "Language.xml", but it is not included after a restart of Word

Screencast: https://streamable.com/7g5lh2

GIF animation:
GIF-Animation • 2022-08-03_11-10-18.gif

How can I resolve the problem?

Thanks for help.

Andy