If you’re calling from another file you edit the pragmas in the file you’re calling from. Seems easy enough.
I actually am not quite clear on the details: one source made it sound like a limited set of scripts was enabled by default. Perhaps someone who knows Perl better can clarify.
If I'm in a Japanese file and want to call a function in a Greek file, I don't see how I can avoid writing a Greek identifier in the middle of the Japanese.
So, no calling functions in other files that use other scripts?
A reasonable restriction is to demand that all characters in any one identifier are from the same script, and that purely typographical devices such as ligatures are banned.