Hands-free/Driving Mode: How to change the reading voice's language (and voice: male/female etc...)?
Go to settings > language and input > text to speech output.

There you can select one of your installed voices.
You can install voices from the Play Store.
My personal best and free is IVONA (https://play.google.com/store/apps/details?id=com.ivona.tts&amp;hl=de)