On Intel Architecture systems, a keyboard is selected during the kdmconfig(1M) part of the installation. To change this setting after installation, exit your GUI desktop environment to the command-line mode. As superuser, type kdmconfig to run the program. Follow the instructions to get the desired keyboard layout.
Additionally you can use the setxkbmap feature to change the keyboard layout simultaneously.
The setxkbmap allows switching the keyboard layout simultaneously when using the Xorg server. This command maps the keyboard. It uses the different command line options. For more information, see setxkbmap man pages.
Open a terminal and type the following command:
$ /usr/X11/bin/setxkbmap cz