If you are using UTF-8 charset you will face a problem with Arabic language
to solve this problem i used this function

<?php
function chunk_split_($text,$length,$string_end)
{
    $text = iconv("UTF-8","windows-1256",$text);
    $text = str_split($text);
    foreach($text as $val)
    {
        if($a !== $val)
        {
            $a = $val;
            $x = 0;
        }else{
            $a = $val;
            $x++;
        }
        if($x > $length)
        {
            $new_text .= $val.$string_end;
            $x = 0;
        }else
        {
             $new_text .= $val;
        }
        
    }
    $new_text = iconv("windows-1256","UTF-8",$new_text);
    return $new_text;
}
?>