You should be able to access Apple Support services in any country that Apple has official representation. As such, should you need to seek support from Apple, this should not be a concern.
All iPads are usable worldwide. All Apple iPad USB power adapters are designed for use with power sources rated to provide 100V AC to 240V AC at 50Hz to 60Hz. Apple iPad USB power adapters also comply with the IEC/UL 60950-1 and IEC/UL 62368-1 standards for use with power sources rated to provide 115V AC at 400Hz (typically found onboard commercial airlines).
While your Power Adapter will be fully usable when travelling internationally, you may require a simple pin-adapter to allow the Power Adapter to be used with AC power outlets in different countries. For example, a Power Adapter designed for an Australian AC Power-outlet will require a simple plug-adapter for the standard European round 2-pin socket. Travel adapters are readily available. Alternatively, you might simply obtain a replacement European Power Adapter when you return to Germany.
WiFi+Cellular models of iPad, sold in different countries, may differ in coverage for additional cellular-radio bands applicable to the country of purchase. That said, the main Cellular-radio 4G/5G bands are relatively universal.
While you are hopefully unlikely to call upon your device warranty, the terms of warranty for devices purchased in Australia may differ from those within EU Member States:
Legal - Apple Products and Australian Consumer Law - Apple
To complicate matters further, Apple also provides an international one-year limited warranty for products purchased in some regions. International Warranty service is limited to the available service level in the country where the warranty claim is made.
Be aware that the optional AppleCare+ coverage, if purchased, is only valid within the country of purchase.
It is generally recommended that you purchase a device in the country within which you intend to spend most time - as this significantly simplifies the warranty position should you ever need to call upon it.