Neither Cpanel nor Helm will support domain names entered with international characters.
They will howver support the name when translated into PUNYCODE.
Use the following URL to convert your Internationalised Domain Name (IDN) into PUNYCODE, and then enter the encoded name into Cpanel or Helm.
e.g. οικοδεσπότης-γάτορ.gr would be encoded into PUNYCODE as xn----plbucfmli7bcghsvcof1l.gr
You would then enter xn----plbucfmli7bcghsvcof1l.gr as the domain nam in Helm or Cpanel.