Преобразование из UTF-8 в KOI8-R:

   use Unicode::Map8;
   use Unicode::String qw(utf8);
   my $koi8 = Unicode::Map8->new("koi8-r");
   $koi8_string = $koi8->to8(utf8($utf8_string)->utf16);

Обратное преобразование 

   use Unicode::Map8;
   use Unicode::String qw(utf16);
   my $koi8 = Unicode::Map8->new("koi8-r");
   $utf8_string = utf16($koi8->to16($koi8_string ))->utf8; 


Другой метод:

   use Encode;
   $koi8_text = from_to($utf8_text, "utf8", "koi8-r");
   $utf8_text = from_to($koi8_text, "koi8-r", "utf8");