If the domain name that you are trying to use in cPanel as a parked or an addon contains non-Latin characters (Chinese, Arabic, Cyrillic, etc.) in its name, it needs to be first encoded by using this or similar tool.
You should then use the converted form of the domain when adding it in cPanel.
Example: If you owned the domain bücher.com its converted alternative would look like this:
In cPanel you need to use xn--bcher-kva.com when adding the domain. When your site visitors type bücher.com, their browsers will automatically convert the name to xn--bcher-kva.com and will then establish a connection to your site.