In the recent versions of minecraft there in no option to change the toggle narrator hotkey. It is set to control+b. I think this is a problem because control key is used for sprinting and the b key is really close to the spacebar and easy to hit with your thumb (in 1.8  I used it as my hotbar hotkey), so its very easy for me to accidentally toggle on the narrator, which is very annoying. I think that it would be very easy to add an option to rebind it to somethink like control+p, so you don't turn it on accidentally.