Domain names containing Arabic, Chinese, Cyrillic, Tamil, Hebrew or special characters are called internationalized domain name (IDN) and cannot be used in cPanel as addon or parked domains in their original Unicode form. To be able to use them, you will have to first encode them into ASCII by using a free converter like this one.
For example, if you have the domain español.com will be converted to xn--espaol-zwa.com. Now you can use xn--espaol-zwa.com to add the domain in your cPanel.