International Day of Sign Languages (23 September)

A serious one for a change. Proposed by the World Federation of the Deaf, accepted by the United Nations in 2018.
WFD "represents over 70 million deaf people worldwide who collectively use around 300 different sign languages."
Yes, 300. There's a list here:
https://en.wikipedia.org/wiki/List_of_sign_languages
A lot of them are highly localized, as you might expect. But they are not all independent local inventions. The table shows that some are historically derived from others, so that we have "families" analogous to spoken-language families.
New Zealand Sign Language was made an official language of NZ by Act of Parliament in 2006. The table says that American SL "is also officially recognized as a language in Canada", but I don't know if that's the same thing.
Practical importance? I don't know. Maybe no more than the International Day.