I don't have any experience with CAboots but with US footwear I always go one size up. Not sure what sizing is like in Germany but living in New Zealand I've found that US shoes tend to be one size too small. I take a NZ size 11 but I always order size 12's if I'm importing from the US.
Hope this helps
P.S You might want to try a pair of these------------ A little more accurate than the CA boots I think and they run a little larger in my experience. I went a size up like I usually do and got a pair of these in size 12, they fit me fine with room to spare (good for adding comfort insoles)!