Doesn't the GECOS field already cover some of this use case?

I must sadly approve of this answer.

And it's not as though a non-Latin-alphabet username would really help that much, since so much text - especially in path names and URLs - is in English. There is, however, the full name of each user, and I'm guessing that should be much easier to have non-Latin UTF-8 in. And for non-computer-literate users who need a lot of hand-holding, they might actually see mostly/only their full names.

I would like to reiterate that I was specifically thinking of logging in at the console, since (as I mentioned) the GUIs are already displaying the GECOS field (which supports full Unicode) in an interactive picker, at least under most reasonable configurations. I do not understand how you're going to get very far at the command line if you can't type in ASCII.

>for them to lean 1 (one) English world

Yes, what a shame they can't just lean one world. Or just learn to live in one English world.
Or just lean on one word to avoid learning English.
Or something.

(yeah, cheap shot, but come on, if you're gonna get on a soapbox about folks learning to spell one word, you really should double check that you spelled *word" correctly, and avoid inadvertently proclaiming that there is one English World - it's the kind of thing that could end up really getting under a Scot's skin).

I used to have a non-ASCII character in my surname, an "ö". After spending many hours of travel mentally preparing for the possibility of a heavily armed but dumb border guard making trouble for me because the UK travel company's software supplier apparently didn't realise that travellers on international journeys might have non-ASCII names (turned the "ö" into like 5 random characters) I started booking tickets with "o" instead. I figured that the kind of ignoranus who wrote the ticketing software above wouldn't notice the missing dots - and anyone who does notice will understand my explanation why I gave a false name. And this wasn't in 1960, this was ca 2001 or later. Remember, this was with a travel company. Not a local bus company, these people did substantial international travel. In fact the brand was "Eurolines" - but they couldn't even handle German names.

Similarly, until 2010 or so I would not use äöüß in filenames. Ever. To this day I still only use my native languages properly for low-risk "user-only" files - so I might use it for a LibreOffice file or a video, but I would not use it for a login username, anything in /etc, and so on. I just don't want the extra hassle. But I'm fairly advanced with IT - how is a typical user supposed to know that some software still can't handle such things, many DECADES after the problem was partially solved with Unicode? Do we really expect children today to learn a 1950s (!) encoding just so they know what characters they can use in a username? Surely there's more useful things that can be taught instead. E.g. pretty much anything else ;)

That being said: I wouldn't hold my breath for non-ASCII login usernames to become reliably usable with the infamous "long tail" of software. But huge progress has been made, and I think it's important to keep going.