Well it is all here... :) in my custom setting:
Letter "c" in full screen video, you can choose what ever suites you.
It is built in fuction to call script within xbmc, in my case I am calling "script.xbmc.subtitles"
So if you would want just this in your kbd file it would be:
Just replace "C" with what ever you want :)
Have a nice flicing :)