My Preferred & Primary language is set to English (The region is however set to Germany) as shown in the image below.
When I try to shut down or restart, I am presented a dialog in German language.
I have tried to solve this by running
sudo languagesetup in the terminal to set the lang by selecting
Use English for the main language then restarting. This had no effect.
defaults read NSGlobalDomain AppleLocale in the terminal outputs