In my experience it is not so much a matter of not working with a comma (as in - error messages), but it does require extra work. One example is the mineral search window. If I change the amount of any single mineral, but don't change the accessibility, it stays on '0.1'. My system uses comma, so it interprets it as '1' instead of '0,1'. If I am only interested in seeing which bodies have duranium on them and don't care about the accessibility, I still need to change the accessibility from '0.1' to '0,1' - otherwise it only finds acc 1 bodies.
This means a lot more work when making complicated mineral searches as I can't simply change the number, but have to write out the '0,' as well.