Hi,
I can see on your screenshots that the language texts of HikaShop are properly displayed in German.
So that means that Joomla finds the HikaShop German language and uses it for the texts when the current language is German.
This means that on your frontend, the current language is not German.
In fact, if I check your website frontend, HikaShop's interface is in German:
monosnap.com/file/onFQkAlsrY5nLwwKZABN8hDzGn1REH
So I suppose that everything is properly setup already.
It's probably just that the language of the user account you're logged in with on your frontend is English. So edit the user account via the Joomla user manager and check the language setting.