Is there any mumble integration features in Unvanquished? I thought there was but I can't find anything about that on the internet, but I found some things like unvanquished transated sentences that indicate such a thing might exist.

Does that exist? Is there any documentation about it?

cl_useMumble and cl_mumbleScale are the two cvars related to mumble. I don't know anything more.

There is also voip i think but no one uses it.