I'm very happy to announce that we're now supporting DNS hosting for all IDN TLDs.
To use DNSimple to manage the DNS for an internationalized domain name go to the Add a Domain page, enter the domain name, leave the Register or transfer this domain unchecked, and press Add Domain.
The domain name can be the unicode string or the punycode transcription. Our system will automatically convert the domain name to the appropriate representation.
IDN registration support is currently limited to .COM and .NET TLDs.