(Hah, I just looked around a bit more, and Wikipedia cites an archived mailing list message that I don't remember seeing before: https://web.archive.org/web/20181027195101/http://blade.naga... I remember at some point Emacs Lisp specifically being cited as an inspiration, but I might be confabulating that, I didn't find a source for it.)
Also, here's a fun paragraph from the opening comments of quail.el (lightly reformatted):
> [There was an input method for Mule 2.3 called ‘Tamago’ from the Japanese ‘TAkusan MAtasete GOmen-nasai’, or ‘Sorry for having you wait so long’; this couldn't be included in Emacs 20. ‘Tamago’ is Japanese for ‘egg’ (implicitly a hen's egg). Handa-san made a smaller and simpler system; the smaller quail egg is also eaten in Japan. Maybe others will be egged on to write more sorts of input methods.]
And now it's more clear to me why that is.
In fact, I think next time I'm writing Common Lisp code, I'm going to figure out how to create Janet's | as a reader macro.
[1] https://news.ycombinator.com/item?id=6094610 [2] https://github.com/emacs-mirror/emacs/blob/master/lisp/progm...