I am currently studying sign language in Germany (ie DGS - Deutsche Gebärden Sprache, german sign language).

In the long term I can not think of anything why it should not be possible but here a few difficulties that come to mind:

1. Sign languages are in general not yet as well understood as spoken languages (the grammar, the vocabulary). For example the University of Hamburg is running the "DGS-Korpus" project[1] in order to create the first real dictionary for DGS, currently there is none. i.e. even humans have not a full explicit understanding of the language (DGS) and afaik it's similar for other sign languages

2. As video recordings are not older than 100 years and the community of native speakers per language is much smaller than for spoken languages the amount of recorded speech is much smaller

3. Large parts of sign languages are very productive. That means that the speaker/signer is not limited to a fixed vocabulary and a fixed grammar but allowed to reenact a situation he is telling about ("constructed dialogue" and "constructed action"[2]). Eg when retelling a conversation the storyteller can shift her body to the left or the the right in order to embody multiple people. Instead of saying "I drove the car. I had to turn left and then I saw her on the right side" the signer can just move as he was sitting in the car, holding the the steering wheel, moving it to the left and turning is head to the right. I would compare that to making "phewww... ohhhhh, whoaaa" sounds in order to tell how the plane you sit in took of. Additionally the signer is allowed to allocate locations around her upper body to establish references to previously mentions objects and refer back to them via pronouns.

4. There is no agreed upon notation for writing down signed texts. Sure there are notations for various hand forms and movements directions but especially the productive part of language mentioned above is hard to formalize. E.g. spacial locations that can be used for placing references are not predefined. Some person still learning the language may only be able to use two positions "left to his body" and "right to his body", but a very eloquent signer may be able to establish even 10 references points in front of him and still enable the audience to keep track of them. Such arbitrary reference points can not be written down in a sensible notation.

5. Various sign languages differ much more from each other than one might initially think. Each sign language has its own grammar and vocabulary. For german sign languages it's not even entirely clear what marks a sentence.

6. Sign languages are not sequential but simultaneous languages ie it's possible to express one thing with one hand and another thing with the other hand in parallel

So some first steps might be:

* find a formal grammar for sign languages

* find a formal notation to write down arbitrary sentences

* collect a large corpus

* Train some AI to translate video data into your notation

* Train some AI to translate the notation from one sign language to another (and to spoken/written language as well)

* Train some AI to translate spoken/written language to your notation for some sign language

* Build an avatar that accepts that notation as input and translates it into movement

[1] http://www.sign-lang.uni-hamburg.de
[2] https://www.signteach.eu/index.php/podcastsall/item/construc...