I'm wondering if it is possible to change the decimal separator in Altium Designer from a "." to a ","? I have looked for it and Googled it but I can't find anything.
As far as I know it is not possible. But you can change the "comma" on your numeric keyboard to make a "dot" with the following registry entry:
REGEDIT4 [HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\Keyboard Layout] "Scancode Map"=hex:00,00,00,00,00,00,00,00,02,00,00,00,34,00,53,00,00,00,00,00
Save this to a file named comma.reg, execute it and when asked, allow Windows to add the changes to the registry.