Check whether your review is a review without text (rating-only). Reviews without text are detected as English by default, as the AI has no information about the guest’s language. You can manually translate the generated reply draft by changing the selected language in the reply field dropdown.
If you wish to always reply to reviews without text in a certain language (e.g., because most of your guests are German). You can create two automation rules, one rule for reviews with text (setting the language settings to your properties preferences), and another rule for reviews without text (putting e.g., German in both language fields to make sure reviews without text that are detected as “English” will also be replied to as German).