> It's certainly not the case that it "will only work for English and a few European languages"; it will work for much of the world.
I respectfully disagree.
Consistently broken in the same way for everyone is better than unreliably working for some people, reliably working for other people, unreliably broken for a third group and reliably broken for a fourth group.
Filenames should be created as the user typed it - don't change the input before storing it.
Filenames should be displayed as the user typed it - don't render output different to what was input.
Tools should match filenames as the user expects it - in this case (hehe) it should perform a case-insensitive match. Ambiguity resolution has to be performed in the case where there is more than one match.
cat > MyFile.txt # Create 'MyFile.txt'
ls # Display 'MyFile.txt'
echo myfile* # Display 'MyFile.txt'
vim myfile.txt # Opens 'MyFile.txt'
The first problem with this is in automated shell scripts: there is no interactivity so the script can't prompt the user
"Which of the following files did you mean to open: [MyFile.txt, myfile.txt]?". This means that a script which relies on 'foo.txt' will fail if someone creates a 'Foo.txt' in the same directory.
Another issue with this is that userspace calls to `open()`, `stat()`, etc aren't able to fail and return a list of case-insensitive matches in the case of ambiguity. This makes handling the ambiguity the applications (very complex) problem - before any `open(fname)` call, the application will first have to `scandir()` to get all the filenames, then perform a case-insensitive match against the list to get all the CI matches, then prompt the user to select the correct one.
> The fact of the matter is, two out of the three most used systems today are case-insensitive
I think it's more that they are case-aware than case-insensitive; after all the filesystem certainly stores the case, and they both retrieve the case correctly.
It's the tooling that faces the user which "fix" cases to prevent two files with the same name in different cases being created.
You can certainly create file 'FOO' and file 'foo' on Windows in the same directory, and then the tools tend to randomly open only one of them no matter which on the user clicked on.[1]
Which is why I say that the actual filesystem is case-sensitive. The user programs normalise the case for the user.
[1] EDIT: I accidentally did this once, and had to write another small tool to remove files with the filename as typed because the normal tools (del, explorer.exe) just randomly choose one file to remove.