Does Dandy understand sign language or literally anyone else
Great question! Actually a good amount of the known cast knows some signs! Here's the specifics tho :D
Mickey and Oswald are fluent but rusty. It'd be janky and unnatural but It'd get the point across. their mother was fluent and taught them it growing up (im going down the epic mickey ds game route for their family and dynamic lol)
Jessica and her husband rodger are also fluent! Jessica learned it specifically because she wanted to go into teaching and felt heartbroken when she couldn't talk to some students directly. She is also fluent in Spanish for this reason. (She and her husband have sign names given to them by a deaf kid :D)
Sonic understands ASL but he doesn't understand signing it back so there's an interpreter for him
The rest of the teachers either only know a few (bathroom, water, lunch, recess. Thats about it) signs or know nothing </3
As for dyles immediate friend group:
Dandy: he's kind of good at it? He can do small talk but not hold an actual conversation. It's also grammatically incorrect and actually SEE (signing exact english) sign language not asl </3
Shelly: she only recognizes specific signs, definitely not able to hold a conversation.
Vee: she's fluent but she's slow. (She just looks up how to sign everything lol)
sprout: he wants to learn, but none of the signs retain so he has to relearn them over and over and over again (they write to each other instead)
Astro: the most naturally fluent of the group, but hes hard to understand as he'd randomly switch which set of arms he's using to sign.
(Only dandy has a sign name, and only because dyle got tired of signing dandicus over and over again when talking about him)
Bendy: not a clue. Never even conceptualized asl as a thing. Believes dyle is making it up on the spot (in the way he really looks up to dyle for it, if that makes sense)
Boris: only knows a few signs, not anything substantial or noteworthy
Mugman: the most fluent of the group! In the same way someone would be the tallest hobbit....
Cuphead: somehow worse than bendy