I'm not familiar with that disc, but most or all Knoppix distros take "cheat codes" at the first boot prompt. See the cheat code section of the wiki for full details. To force language on a non-english distro you would type knoppix lang=us (assuming you have a us and not a uk keyboard). You can also include other cheat codes on the same line. That = can be tricky, as it is in different places on different keyboards. If the disc you have is booting in German and you have a us keyboard then the = is shift-zero, otherwise you may have to hunt for it.