As someone who needs non-ascii characters to write my name: please don't. You are making things worse just to be "courteous" about something we don't care about and will actually be annoyed at if we have to find how to write a letter in the keyboard or worse case scenario, figure out how to change the layout to the correct one before I even logged in.
Likewise. My last name contains a non-ascii character. In ~2009 I started at a company whose admin conveniently set up an account for me on their Ubuntu server... on which no-one could then log in locally because the login manager crashed when trying to display the list of users. I logged in via ssh and changed my name to the nearest ASCII equivalent.
I always feel slightly worried on sites that demand that I give my full legal name (such as the US ESTA form), and then refuse to handle it because it includes "illegal" characters.
"Legal name" is a catch-all term that usually means "approved for use on government issued ID". Are there instances when that's not always the case and some forms of ID (not just, say, an ID card, but also in tax filings, for example) actually have different rules? Amazingly, sometimes yes. But usually that's what it means.
Legal system as in court of law? They tend to use more letters than I have in my actual passport (definitely more than fits into mrz) and depending on which court we talk about they also use different alphabets. They also assume certain structure in those nsmes, which differs from one court to another.
Yes, I had a pleasure do deal with two courts that use two different alphabets this year. They one of the two referenced the other. The name written in neither of two matches whats actually written in my passport. It isn't a complicated name by any reasonable metric.
Taxes are easier -- they just ids and names are display only kind of stuff, sourced from the base registry.
This has happened to me with passwords containing foreign characters. The system would accept it, but further logons would be impossible. Now I always strip diacritics to be safe.
A friend mentioned using control characters in passwords... like ^F and ^B, but not ^C because that's the interrupt character. Feels vaguely risky to me (does ^U empty the line? does ^W delete the last word? does your terminal emulator do some weird encoding like it does for cursor keys?) but if it works, why not?
I suspect I have run into a couple bugs because of password generators putting characters that some backend system cannot process in the password. Halfwish they just did DKWhhjwqjkwqjmHSJKHAIUHQwdmlsadkl instead.
I sometimes use this as a quick test of software quality. If it can't handle non-ascii characters in 2024, then it will probably be more trouble that it's worth.
