1. Set your system/game to German.

2. Try to input a floating point number, e.g. edit the maximum travel distance of a piston

The keyboard will show a ',' instead of a '.', but not accept the input using the comma.

If you use the + and - buttons, the displayed number will also use a ','. Those numbers appears to be localized to German, although the rest of the game is not, so that looks a little strange anyway.