Hi, thanks for reaching out. The following documents provides list of supported languages and regions for custom neural voice. Furthermore, with Custom Neural Voice Lite (public preview), you can create a model for demonstration and evaluation purpose. No application is required. Microsoft restricts and selects the recording and testing samples for use with Custom Neural Voice Lite. You must apply the full access to Custom Neural Voice in order to deploy and use the Custom Neural Voice Lite model for business purpose.
--please don't forget to Accept Answer if the reply is helpful. Thanks.--