Afaik there is no translation/multi-language support for address lists, so that's the expected behavior. If your tenant is German and all users prefer the language, you can rename any existing lists via Set-AddressList, but keep in mind this will affect the display names for all users.
The other side of the coin is the regional settings on the device/browser - depending on the language configured therein, some UI elements will be translated. But afaik this does not apply to Address list entries.