No I get that forcing alphanumeric is a very arbitrary decision that is far from natural to a large part of the world's population and normally I would advocate

No I get that forcing alphanumeric is a very arbitrary decision that is far from natural to a large part of the world's population and normally I would advocate for everyone to adopt Unicode. However UTF8 passwords is a recipe for disaster that I want no part of. Passwords should be random byte strings, not a random piece of human language. Now technically alphanumeric isn't quite the same as a random byte-string but it is the one subset of text for which you can be almost certain that it will always be represented by the same bytes (although I suspect someone will point out an exception). Note that not only does Unicode have several different binary representations, but even a sequence of code points has 4 different canonicalizations, that I cannot guarantee will always remain the same.