The codebase for the C-Toolkit is old. Really old.
Well, there's no support for Unicode characters longer than 8-bit which may result in weird/garbage characters on screen.
The character-handling needs to be rewritten in order to support Unicode characters.
Use other encodings such as US-ASCII, ISO-8859-1 for the JVM (as a launch parameter property) and in Toolkit.setEncoding(String encoding) until this has been fixed.