Who decides when new punctuation is to be created?

There isn’t one. There is no governing body on language usage, grammar, or punctuation, at least as far as English is concerned. (The Academie Francaise does make edicts on what is acceptable in French, and what is not.)

Language is considered living and evolving.

Most punctuation was decided upon by typesetters. If the need for another punctuation mark arises, it would nowadays be decided by a font designer and whatever keyboard manufacturer agrees to design a keystroke for it. That is why some but not all keyboards have € for the Euro.

It’s not quite the same thing but Ray Tomlinson the inventor of email, picked the @ symbol to separate user from host because it wasn’t much used at that time. It quickly became an international icon that everyone knows and uses.

I would not be surprised if emojis become punctuation within a generation or two.

I was curious to know whether other languages share our punctuation. I did a Web search and found this site What I gather is that there is a lot of similarity but also some differences. Note that this is a commercial Web site; don’t bother following the language links.

One fun thing that I learned is that some languages that are written from right to left, like Arabic and Persian, use commas and question marks that are the mirror image of the ones we use. Hebrew, which is also written right to left, uses the same question mark and comma symbols as we do.