Here is the mcinp's version of mb_str_pad bugfixed: 

<?php
function mb_str_pad($input, $pad_length, $pad_string=' ', $pad_type=STR_PAD_RIGHT,$encoding='UTF-8'){
        $mb_diff=mb_strlen($input, $encoding)-strlen($input);
        return str_pad($input,$pad_length-$mb_diff,$pad_string,$pad_type);
    } 
?> 

Still working correctly only if $pad_string is non-multibyte string