>If filesystems are using binary data for filenames, there can be a case when is really no way to address a file by typing its name, even if you can type in that language
You could do that trivially in UNIX since forever.
Don't know about other UNIXes, but at least on GNU/Linux, neither IMEs nor filesystems are working with text data - it's all binary strings (with a few restrictions, like unacceptability of NULs). The only place where those binary strings are converted to text is when they're rendered (and this may cause some encoding-related oddities). So, sure one can do that.
I would've actually preferred for identifiers to be Unicode text strings.
You could do that trivially in UNIX since forever.