@Henri - This issue was fixed in version 0.1.3-1.1maemo12, currently in testing: http://maemo.org/packages/package_instance/view/fremantle_extras-testing_free_armel/supertux-stable/0.1.3-1.1maemo12/
You only need to configure the keys in the keyboard settings according to your keyboard layout.

Good work, but i need to use the English keyboard for moving while in the world map. I'm waiting for the new version!