Total side note, and shameless self-promotion, but The "U.S. International - Scientific" Keyboard Layout - Michael Goerz
Still: do not require Unicode in the public API of your package; you can use something like
function f(; eta=1.0, η=eta) end
if you want to allow for Unicode in your API, in addition to ASCII. Certainly, do not require it in your package name. Internally, you can go wild. But also: know your audience. What might be a useful addition to the heavily mathematically educated users of one package might severely limit the userbase of another. I’d strongly recommend keeping things in English, as the lingua franca of scientific computing. I would actually support having this as a requirement for the General registry, and then have separate “regional” registries for Spanish, Chinese, etc. It’s certainly worthwhile to also have code in one’s native language, especially for very young students, even if that means that code can’t have a global reach.