Knoppix is available in German and English ISOs
plattypus1,
Do you have an especially old Knoppix disc?
You should be able to boot in english by specifying the following at the boot prompt:
knoppix lang=us
However, english versions have been coming out for months. There are two simultaneous releases. The German release has the letters "DE" in the filename and the english version contains the letters "EN".
Both are essentially the same except for the settings in the floppy disc image used to make the CD bootable.
Regards,
Nathan Chilton