In the category view I see categories with labels in German (see attachment).
Is that correct?
Absolutely.
When a database is created, IMatch populates the standard categories using the category schema of the current IMatch user language (if available).
You can delete the categories if you don't want them or replace them with the English counterparts via the Category Import using C:\ProgramData\photools.com\IMatch6\Presets\system-en.imcsx