Changing KDE language settings messed up locale

Hello everyone,

I tried to change the change the language in KDE’s settings in the “region and language” section. I did this because I wanted the Java compiler to show its messages in English, and I thought everytime I needed it I could temporarily set the language to English and then back to Austrian German, which I use otherwise.
When I tried to change the settings I got a warning that my system can’t auto-generate locales, so I changed it back (or I thought so) and didn’t think about it anymore.

Since the next reboot after the fiddling the GUI is partly in English, partly in German.
I tried to change locale settings in the terminal and generate new locals, but that didn’t help.

The output of locale is as follows:

locale: Cannot set LC_CTYPE to default locale: No such file or directory
locale: Cannot set LC_MESSAGES to default locale: No such file or directory
locale: Cannot set LC_ALL to default locale: No such file or directory
LANG=de_DE.UTF-8
LC_CTYPE="de_DE.UTF-8"
LC_NUMERIC=de_AT.UTF-8
LC_TIME=de_AT.UTF-8
LC_COLLATE="de_DE.UTF-8"
LC_MONETARY=de_AT.UTF-8
LC_MESSAGES="de_DE.UTF-8"
LC_PAPER=de_AT.UTF-8
LC_NAME=de_AT.UTF-8
LC_ADDRESS=de_AT.UTF-8
LC_TELEPHONE=de_AT.UTF-8
LC_MEASUREMENT=de_AT.UTF-8
LC_IDENTIFICATION=de_AT.UTF-8
LC_ALL=