How to extend the ctl-x 8 map?

[Skip Montanaro]

I found myself at a loss to type Ł characters in an email today. I realize
I can type CTL-X 8 RET and enter the Unicode phrase corresponding to that
letter, but would like something a bit less verbose, like CTL-X 8 / L. I
see an iso-spanish function in iso-cvt.el and corresponding translation
table, but don't understand how it's involved (if at all) with the CTL-X 8
keymap stuff. Does someone have an example of extending the reach of that
keymap?

Thanks,

Skip Montanaro