When will we be able to hear the Navajo language to assist with our learning ?
No one really knows.
To shed some light, consider the case of Swahili:
The Swahili course was supposed to get audio "shortly" after its public release in February 2017. There were a number of official announcements. It was even announced that all the recordings had been completed over a year ago. Swahili graduated "beta" months and months ago. Still no audio.
Maybe things will be different with Navajo, who knows?