Agreed, KiXtart only really supports extended ASCII / single-byte characters. It has partial support for multi-byte characters, but there is not really any practical way to use it.

You may be able to change your "code page" to display the characters in the correct form on a console, but that is basically just a typeface change - the underlying characters are still the same.

You can create unicode output streams using FSO, but they are a bugger to manage. What exactly do you need to generate the Czech text for?