It is not possible to check for availability a domain name that contains national symbols, in UX1 one may see an error message when trying to click the "Submit" button.
Transfer not supported. Domain lookup service is not available at the moment.
A WHOIS checker is used to validate the domain name responses. When trying to validate a domain name with any national symbol in it, the WHOIS checker response cannot be processed by the platform correctly. This behaviour is considered as a bug OA-4455.
Contact your Technical Account Manager or Pooled Technical Associate Team at firstname.lastname@example.org to clarify the status of OA-4455 as no workaround is possible.