HERE WeGo relies on the OS (both Android and iOS) for the voice options it offers. This means that the text-to-speech (TTS) system installed on your phone will be the one through which we offer our list of voices within the app. If you wish to use a type of voice guidance that is currently not on the list, you may install your desired TTS directly from your phone's system settings (outside the HERE WeGo app). Your TTS options will vary depending on your device model and your OS version. 

To change the voice's speed, please check the voice options under your phone's settings.