IDN stands for Internationalized Domain Name. IDNs are domain names that contain characters from non-ASCII (American Standard Code for Information Interchange) character sets. For example the characters õ, ä, ö and ü used in Estonian languages are non-ASCII characters. Same applies to Swedish å, Romanian ș, Greek and Cyrillic alphabet.
At the moment EE, EU, FI, COM and NET IDN domain names can be ordered through Zone. You can place an order HERE.
The maximum length of a IDN cannot be more than 63 characters. This limit applies after the name has been converted into an ACE string for use by the DNS (Domain Name System). For example, abcdef.eu is 6 characters long, xyz.eu is 3 characters long, JÕULUD.EU, however, is considered 13 characters long, because after conversion it’s ACE string is www.xn--bcher-kva.eu. Although, after the conversion e.g. the length of the domain Ä.EU would be 7 characters in ACE string, it cannot be registered, as EU domain name should be at least 2 characters long.
A great tool that will help you find out ACE string of an IDN domain can be found HERE.
Different alphabets cannot be used in single IDN domain. Mainly to prevent the use of homoglyphs in domain names. Homoglyphs are characters from different scripts/alphabets that look so similar that it is difficult to tell them apart just by looking, but have different UNICODE numbers but look identical. For example, cyrillic character “a” and latin character “a” identical by looking, but have a different UNICODE numbers accordingly 0430 and 0061. Therefore, in order to avoid confusion and legal disputes, different alphabets cannot be used in single IDN domain name.