I feel like you'd lose most of the advantage of a voice interface if you had to learn a new (and presumably difficult) high-bandwidth vocal signal language. It

I feel like you'd lose most of the advantage of a voice interface if you had to learn a new (and presumably difficult) high-bandwidth vocal signal language. It might still be useful for some niche scenarios where it's very important to have your hands free or to operate over an audio channel, but the real notable advantage of a voice interface is that most humans already use speech as their primary method of communication with other humans.