Hi, Speedy_13!
Thanks for taking the time to contact us and let us know you have a doubt regarding language settings on your Surface Duo.
If you buy a Surface Duo from German distribution and change the Android language settings to Polish, you can also change the screen keyboard to Polish/international QWERTY. The keyboard will not stay as German QWERTZ unless you choose that option in the keyboard settings.
To change the keyboard layout, you need to go to the Virtual keyboard menu in the Settings and select the keyboard app that you are using. Then, you can choose a language or layout that matches the Polish/international QWERTY keyboard.
I hope this answers your question. If you have any other questions, please feel free to ask me. I’m always here to help!