Sorry for the late answer. I am not sure if I understand correctly. Are you running Knoppix from CD or USB ? And if I understand right you want to boot Knoppix with German locale, but be able to switch between German and Brazilian Portuguese layouts. Or you want to boot in German with Brazilian keyboard layout.
If you run Knoppix from USB it is a simple thing, but if you run it from CD you have to remaster it which is a lengthy process.