Setxkbmap: Multiple layouts with different variants

You can set

localectl set-keymap --no-convert <keymap>

Which will change the keymap used at startup. Substitute keymap here with the one you'd like to use. Also ensure that you change your other locale information.

You could try kbindkeys, numlockx and a slightly customized keyboard.

Once you install xbindkeys, you have to run it. It will tell you what to do to create the basic configuration.

Then you use xbindkeys -k to identify the key and modify the configuration file (it's all documented in the default configuration file).

At last, I suggest you run xbindkeys -v -n to see if everything works. If it does, you can run xbindkeys for that session and maybe add it to your startup scripts.

In my case, the Windows key (right) does the binding, and my ~/.xbindkeysrc is:

"numlockx toggle"
    m:0x10 + c:134
    Mod2 + Multi_key

Now you can add the mappings. You will use the fifth and sixth levels (numlock and shift+numlock).

At the top of /usr/share/X11/xkb/symbols/cz, right after:

default  partial alphanumeric_keys

add this snippet:

xkb_symbols "with_numpad" {
    include "cz(basic)"

    key.type[Group1] = "EIGHT_LEVEL_ALPHABETIC_LEVEL_FIVE_LOCK";
    key <AC07>  { [         j,          J,   apostrophe,     NoSymbol , 1, 1] };
    key <AC08>  { [         k,          K,      lstroke,     NoSymbol , 2, 2] };
    key <AC09>  { [         l,          L,      Lstroke,     NoSymbol , 3, 3] };
};

Now, when you press the window key (right), xkeybind will set numlock, which in turn will make J,K,L and so on return 1,2,3.

Last step, set the new keyboard with:

 setxkbmap cz with_numpad