root/compat.php

<?php

if (!function_exists('mb_strlen')) 
{
  // from Typo3
  // author Martin Kutschker <martin.t.kutschker@blackbox.net>
  function mb_strlen($str, $encoding="utf-8") 
    {
      if($encoding != "utf-8")
    { return -1; }

      $n=0;

      for($i=0; isset($str{$i}); $i++) 
    {      
      $c = ord($str{$i});

      if (!($c & 0x80)) // single-byte (0xxxxxx)
        $n++;

      elseif (($c & 0xC0) == 0xC0) // multi-byte starting byte (11xxxxxx)
        $n++;
    }

      return $n;
    }
}

if (!function_exists('mb_substr'))
{
  // from Typo3
  // author Martin Kutschker <martin.t.kutschker@blackbox.net>
  function mb_substr($str, $start, $len=null, $encoding="utf-8")
    {
      if($encoding != "utf-8")
    { return -1; }

      $byte_start = utf8_char2byte_pos($str,$start);

      if ($byte_start === false) 
    return false; // $start outside string length 

      $str = substr($str,$byte_start); 

      if ($len != null) 
    {
      $byte_end = utf8_char2byte_pos($str,$len);

      if ($byte_end === false) // $len outside actual string length
        return $str;
      else      
        return substr($str,0,$byte_end);
    }

      else return $str;
    }

  function utf8_char2byte_pos($str,$pos) 
    {
      $n = 0;  // number of characters found     
      $p = abs($pos); // number of characters wanted 

      if ($pos >= 0) 
    {
      $i = 0;
      $d = 1;
    } else {       
      $i = strlen($str)-1;
      $d = -1;
    } 

      for( ; isset($str{$i}) && $n<$p; $i+=$d) 
    {
      $c = (int)ord($str{$i});
      
      if (!($c & 0x80)) // single-byte (0xxxxxx)        
        $n++;
      elseif (($c & 0xC0) == 0xC0) // multi-byte starting byte (11xxxxxx)
        $n++;
    }

      if (!isset($str{$i})) 
    return false; // offset beyond string length 

      if ($pos >= 0) 
    {
      // skip trailing multi-byte data bytes
      while ((ord($str{$i}) & 0x80) && !(ord($str{$i}) & 0x40)) 
        { $i++; }
    } else {      
      // correct offset
      $i++;
    } 
          
      return $i;      
     }

    if (!function_exists('mb_strtolower')) {
      function mb_strtolower($msg, $encoding) {
          return $msg;
        }
    }
}