I wonder if, like with lip reading, they switch from American English to a different language that's not so peculiar they would have and much less error rate
reminds me of the handwriting recognition language Graffiti from palm/handspring days.
It ended up altering my handwriting even after I stopped using it.
I suppose Spanish or German would be easier to recognize than English, due to the more distinct sounds, but Chinese would be much harder, due to the tones.