It's not a different voice so much as a synthesized approximation of the main voice. You can disable it through settings if you don't like it.
I haven't had any issues with mispronunciations yet. I'm actually very pleased with the system. The auto volume reduction and beep are nice. It gets my mind back on getting where I wanted to go instead of just driving. Which is apparently a serious problem for me, the car is just too much fun to drive.