Joomla has an extension already for IDN Domains.
I used this as a base for a project & it worked well.

Here are the file locations

http://api.joomla.org/Unknown/_simplepie—idn—idna_convert.class.php.html

I realize that IDNs are really being embraced by developers. One of the problems is many are sitting on valuable domains. With development, developers know what needs to be fixed or improved on. If you just sit on your portfolio you won’t even realize what advances are available.

Looking forward to developing more over the weekend with the team.