TYPO3 Core

The language of our admin is set to "german" and also TYPO3-sitelanguage, but our CKEditor is always in english in TYPO 12.3.0 (non-composer).

Without language-settings for RTE the attribute "options" in HTML-Code is

"language":{"ui":"en","content":"en-us"}

with language-settings for RTE "editor.config.language.content: de" and "editor.config.language.ui: de":

"language":{"ui":"de","content":"en-us"}

The detection in https://github.com/TYPO3/typo3/blob/main/typo3/sysext/rte_ckeditor/Classes/Form/Element/RichTextElement.php seems not working and propably the language-files for other languages are missing?!