this is a big ugly hack and gives far from complete support for these special characters. but still it is useful in some situations like for buttons or comment boxes in your gui.
w= Window(Umlaut.fix("åäö test"), Rect(100, 200, 150, 150));
Button(w, Rect(10, 20, 130, 40)).states_([[Umlaut.fixAll("schööön")]]);
Button(w, Rect(10, 70, 130, 40)).states_([[Umlaut.fixAll("Tätigkeit heiß")]]);
all supported characters... (more can be added on request)
update: there is also asciiCorrect in the wslib quark by wouter snoei
note: broken in sc3.9 under osx