You can add/change the keyboard command for any menu item in any Mac app via your Mac’s system preferences. It is under Keyboard preferences. Prior to Snow Leopard you need to redraft the app to see the change take effect.
do you possibly know the way to type the application command in the shortcuts window?
I have tried
Format>Text>Writing Direction>Right to Left
and
Format/Text/Writing Direction/Right to Left
and
Format… Text… Writing Direction… Right to Left
and
Format,Text,Writing Direction,Right to Left
but none of them work - and i obviously have no idea how to do it the right way!