The app has a Chinese localization and runs with Scheme options (see image).
When I hit the text field, I would expect a Chinese keyboard and not a German one.
I only see German, English and Emoji keyboards.
Is there any way to tell the Simulator which keyboard should be used by default?
Unfortunately, this is not automatic. You should manually add a Chinese keyboard and make it the default.
Navigate to Settings/Keyboards, add the Chinese keyboard under Keyboards and drag it to the first place of the list after clicking on Edit.