Read this and you will understand :
(from Moderbill support)
I've tried everything I can think of. The cURL post that is coming from ModernBill is being sent as UTF-8, the CGI class used by the Plesk wrapper is declared as UTF-8, and if I print the shell command to screen, it has UTF-8 characters. As far as I can see the problem is with Perl sending the command to get executed. If you have a Perl programmer on hand, you can look further into the plesk_wrapper.cgi file to see if it's possible. At this point, I don't see that it is possible. Plesk Expand works because it does not rely on the command-line creation utilities. It is an XML based API and I have tested it (with Greek characters incidentally) and know it works. You might want to contact Plesk again, but I doubt that they will do any more development on the wrapper file, though it was originally theirs. I'm sorry I can't give better news on this. I really wanted this to work with 7.5, but that does not appear possible.