Internationalised (IDN) Domain Names work by encoding the domain name using a system called Punycode.
When you wish to add an IDN domain in cPanel (parked/addon) or in WHM, you need to convert the domain name into Punycode for the encoded version of the domain name using a Unicode to Punycode Converter tool.
Then when the user enters a URL containing an IDN domain into the web browser, it will convert the IDN domain into Punycode and resolve that domain.