The site is using automated translation through Deepl.
First thing is: German has been set as main language, but translations are made from English. I don't know how this works and what settings have been made to achieve this. Maybe the issue described below is caused by this setting.
The real problem:
Some strings are missing in the translation editor, and some are still shown on the frontend in English though the correct translation is in place in the translation editor.
Example hidden link: The text left to the image is missing in the translation editor, "Back" on the top left is correctly translated "Zurück" in the editor but still displaying in English.
Thank you for contacting WPML Support, I will gladly help you.
According to your debug.info, the WP memory limit needs to be increased, WordPress uses 40Mb as default and the minimum requirements for WPML are 128 MB. (Kindly check this page: https://wpml.org/home/minimum-requirements/)
You can increase it by adding the following code in your wp-config.php file right before the line: /* That's all, stop editing! Happy publishing. */