You would probably have to change the entire iPad to German under Settings > General > International > Language. If VoiceOver supports German, that should do it; but honestly I don't know. Don't panic when it goes into a kind of reset. This is necessary to change all the system labels and such.
Shouldn't hurt anything to try, and you can go back to your previous settings if it does not work.
This will change a lot of other default settings, like how date, time, telephone numbers, etc, are displayed. You can force the Region Format back to what you want in the International settings.
In the same area you can set up multiple keyboards for different languages, so you can leave it in German and still do whatever editing you like with your normal keyboard if you like. When you have more than one keyboard you will see a world key next to the space bar. It will allow you to switch between them.