The english wording here is: "No recommended extension could be found matching 'test', displaying results of the search in all extensions.". You can change the translation there: https://l10n.xwiki.org/translate/xwiki-platform/xwiki-core-resources/de/?checksum=1be5d936f23f7db3
I'm going to close this ticket, as it can be solved directly by changing the translation.