Hi,
Language file missing for ctools current 8.x-3.4 version and this is creating an error for german language installation. Please refer to the main site ticket for this issue.

https://www.drupal.org/project/ctools/issues/3133715

NÜTZLICHE LINKS

[DE] Translation Tracker (Issue-Übersicht)
https://www.drupal.org/node/2917376

Richtlinien für Übersetzungen des Userguides (in Englisch):
https://www.drupal.org/docs/user_guide_guidelines/guidelines-translating...