I researched adding hand motions.
Among the vanilla studio features, there is a feature that overrides only hand poses. (anim -> Kinematics -> Hands)
I can add hand poses/motions to the feature.
However, there are several obstacles that put it off.
One of them is that Sideloader needs a code change to accept the mod.
It's a simple change, but users need to update Sideloader.
And another thing is not convenient to use or add.
Because the vanilla feature only provides about 21 hand poses, So it is not a big problem to select a specific hand pose with only the Next and Previous buttons, but If I add hand motions, I will add more than 100 as the first hand motions mod.
So, Similar to character maker pose feature.
I'd like to add a lot of things there, but it's inconvenient to use/add them with the Vanilla UI and game logic.
TL;DR, We need to create a plugin to add and use hand motions in a sane way.
Back to the point, I compared many references at ASLU and ASL Love and many more to check the source and actual sign language.
Some differences were found between source and actual sign language in cases such as pointing at a body part or moving two hands closely.
A common issue is that the distance between the hands is farther than the actual ASL sign. And the fingers do not grip accurately (especially the thumb).
I have corrected them, but still I do not recommend my ASL animations mod as a resource for learning sign language ^a
Motions are in Anim -> Animations -> Kohai -> ASL (NOITOM)
Let me know If you find any issues or parts that must be improved.
DL : NOITOM_American_Sing_Language_Animations_for_CharaStudio_v0.9.0.zipmod