Inspired by the lcfirst function a simple mb_lcfirst to cope with multibyte strings:

<?php
function mb_lcfirst($str, $enc = null)
{
  if($enc === null) $enc = mb_internal_encoding();
  return mb_strtolower(mb_substr($str, 0, 1, $enc), $enc).mb_substr($str, 1, mb_strlen($str, $enc), $enc);
}
?>