It's there already. [Only registered and activated users can see links. ]

Credit goes out to turboccc for originally pointing it out:
Hi all,

I was told today Garmin has an Avatar voice on their site here: [Only registered and activated users can see links. ]
It is an encrypted voice that works on most newer gps model, but not on Garmin XT. For older models or Garmin XT software, you can try this one: [Only registered and activated users can see links. ]

It is not perfect, but 90% is pure na'vi language. Only a few exceptions have been left in English.