Interesting issue...
I have found all files. Though not solved the problem.
In Joomla the translation is as it should be. Also in CB Login module.
My guess is that there is something somewhere in conflict where EN overrides the other language specifically for this little string.
My knowledge in code is too poor to find the exact problem, thus the solution. But I definitely welcome some expert to find it and hope this information/guessing led somewhere. It doesn't look very smart to have everything else translated but this little thing.
/C