Learning sign language for your alters that dont talk? Heck, yeah!
One of our littles is a symptomholder of our autism and is non-verbal, one of us doesnt speak due to trauma. Can I speak? Yeah. Am I learning it anyway for a better life? Heck, yeah.
Its an really important skill to have and can make so many people happy and is so crucial. Also, if you have autism or trauma (or find speaking hard for any other reasosns) then ITS OKAY TO SIGN.
If you arent disabled or deaf but have time and resources then go learn, its gonna make somebody so happy in the future!