A little while ago I wrote about creating some very large hands and fingers in Second Life in order to investigate sign language.
I had some static hands and I was trying to find time to write a script to help animate them, so they could take positions for various signs.
At the ITE expo I came across the stand for the Pupeteer scripts by Todd Borst (his shop is landmarked on his profile in SL)
Picture from snapzilla
With this I was able to prove that the hands would at least work in some form.
So it needs a bit of work, but as Roo pointed out we could make the sign lexicon a user generated set of content. People creating their own signs and providing them to all the users of the “device”.