xmlencode.php

<?php

/**
 * Converts UTF-8 to XML-safe HTML entities: Изложение => &#1048;&#1079;&#1083;&#1086;&#1078;&#1077;&#1085;&#1080;&#1077;
 */
function xmlencode($string) {
  $string = (string) $string;

  // Replace < and ' and & etc.
  $string = htmlspecialchars($string, ENT_XML1 | ENT_QUOTES);

  // Replace ë etc.
  $string = preg_replace_callback('#[\x{0080}-\x{00ff}]#u', function($match) {
    return '&#' . ord(utf8_decode($match[0])) . ';';
  }, $string);

  // Replace Russian etc.
  $string = mb_convert_encoding($string, 'HTML-ENTITIES');

  return $string;
}