[Gelöst] fetal error

Background of the issue:
I am trying to get the Arabic interface to work correctly on the frontend. I started scanning items in Theme and plugins localization, and then the Arabic interface stopped working and showed a fatal error. The issue can be seen at: versteckter Link

Symptoms:
The Arabic interface no longer works and shows a fatal error.

Questions:
Why does the Arabic interface stop working after scanning items in Theme and plugins localization?
How can I fix the fatal error to ensure the Arabic interface works correctly?