Language mix

Hello, I have a big problem with my woocomerce store. After a week of research, it now looks like unfortunately your plugin is responsible.

There is a mixing of German and English when I use the plugin. Here are a few examples …

The annotations in wordpress become alternating German/English:
https://ibb.co/1r2YYkF

Customer mails are in German and English:
https://ibb.co/prW74Qw

The website is set to “German (Sie)”, the admin account is set to “German (Du)”.

The problem persists even when I deactivate the plugin and EVEN when I delete it. So I can not get rid of this problem once it exists. Very strange …

For testing, I installed a backup from April, where everything was still good. Then I installed the plugin and since then the error is back.

Please help me, I can not start my online store like this.