Internationalized domain names (IDN) and DNS / Bind9 problem

To use domain names with special characters ( παράδειγμα.δοκιμή or مثال.إختبار), you need to transform them into proper format.

To accomplish that, we use idn command from libidn package.
It should be included in base repository so simple: yum install libidn would suffice.

To get real name of domain you need to have UTF-8 terminal coding enabled, then run:

idn παράδειγμα.δοκιμή

The result should be: xn--hxajbheg2az3al.xn--jxalpdlp
This is now your domain name and to include it in Bind9, you just have to set it in config file. Example:

#### My greek domain ####
zone "xn--hxajbheg2az3al.xn--jxalpdlp" {
        type master;
        file "mydomain.zone";
};

I strongly recommend you to comment these IDN’s, so you will know exactly which domain is which, without the need of reversing the transformation.
Note: You should set mydomain.zone zone same as any other domain.