In PHP, this function is used to convert from one cyrillic character set to another.

    convert_cyr_string(string,from,to)

In the above syntax "string" specifies the given input to be split,"from" specifies what Cyrillic character-set to convert from "k - koi8-r", "w - windows-1251", "i - iso8859-5","a - x-cp866","d - x-cp866","m - x-mac-cyrillic", "to" specifies the character set to be converted to.

    <?php
    $str= "How are you!æøå";
    echo convert_cyr_string($str,'w','a');
    ?>

    Hello world! æøå
    Hello world! ¦è¥ 

In the above example the string is converted from "windows-1251" character set to "x-cp866".