Multilanguage german Umlaute

I'm having problems using german Umlaute like "ä" or "ö" in my xml-layout definition (fo example creating a button with the caption "Über"). The aplication crashes instantly.

Open core.font in MyGUI_Media and add your symbols codes there. Add line or several lines like<Code range="x y"/>Where x and y is start and end of interval where Umlauts are.

sorry, I don't get it. Could you explain that a bit more?
Thanks