You have to convert the IDN domain to punycode before you can do a WHOIS. There are online conversion tools here: http://mct.verisign-grs.com/index.shtml
You need to convert it to punycode at this url and then perform whois search. For example: The punycode of the domain you mentioned is "xn--pw0a62s.com"
I have revised www.saferwhois.com to allow direct input of IDN domains. No conversion to punycode required. Feedback appreciated. I know I have to add more domain extensions.