Engadget:

Yesterday, version 4.26 of the app quietly appeared in the App Store, which allows iOS users to “record your own voice directions to guide you on the road.”

To access the voice recording option, go into Waze’s advanced settings and hit “Sound & voice.” Then tap the “Voice directions” option, which takes you to a screen that offers the option to record a new voice. The system will then lead you through quite a few prompts to record your own directions, so make sure you set aside some time to go through every option.

You can see a lot of people will set up, “Turn left, dummy!” as their voice prompts.