The voice tab allows you to select your bot's language and voice.
You can use a server generated voice or native device voice.
You can use a native voice on Android and iOS mobile apps, or on Chrome or other web browsers that support the HTML Speech API.
This list of native voices depend on the platform and OS, and the devices configuration.
A server voice is consistent across all platforms.
If you use a native voice, and the browser or platform does not support TTS, then the server voice will be used as a fall back.
If a native voice is set, and it is available it will be used, otherwise any voice for the language will be used, otherwise the default native voice.