Во первых хочу поблагодарить автора оригинального кода за очень простое и красивое решение.

Комментарии в теле кода вполне достаточны , хочу только заметить,что от оригинала данный код отличается одной функцией - если поле alias не ="" (не пустое ), то новый псевдоним не создаётся. Это позволяет модифицировать псевдоним вручную при необходимости.

 
/*==============================================================================
  Title: AutoAliasRus2Lat
  Category: Plugin
  Author: Predvoditelev Sergey
  Author URI: http://predvoditelev.ru/blog/
  Version: 1.0.0
  Last Update: 07.12.2007 19:30
==============================================================================*/
 
/*==============================================================================
Описание:
Данный плагин при сохранении страницы автоматически создает псевдоним (Alias)
для страницы на основе её заголовка (Page Title), при этом символы кирилицы
заменяются на транслит.
==============================================================================*/
 
/*==============================================================================
Данный плагин основан на популярном плагине для WordPress - RusToLat.
Побробнее об RusToLat:
Plugin Name: RusToLat
Plugin URI: http://mywordpress.ru/plugins/rustolat/
Description: This plugin convert cyrillic characters in post title to latin characters. 
Very usefull for russian-speaking users of Wordpress. 
You can use this plugin for creating human-readable links. 
Thanks to Alexander Shilyaev for idea. Send your suggestions and critics to
 <a href="mailto:skorobogatov@gmail.com">skorobogatov@gmail.com</a>.
Author: Anton Skorobogatov <skorobogatov@gmail.com>
Contributor: Andrey Serebryakov <saahov@gmail.com>
Author URI: http://skorobogatov.ru/
Version: 0.3
==============================================================================*/
 
// Вы можете выбрать стандарт, по которому будет производится транслитерация заголовков.
// off - Отключена
// iso - ISO 9-95
// gost - ГОСТ 16876-71
// По-умолчанию используется ISO 9-95
$rtl_standard = 'iso';
 
global $alias;
global $pagetitle;
 
$gost = array(
   "Є"=>"EH","І"=>"I","і"=>"i","№"=>"#","є"=>"eh",
   "А"=>"A","Б"=>"B","В"=>"V","Г"=>"G","Д"=>"D",
   "Е"=>"E","Ё"=>"JO","Ж"=>"ZH",
   "З"=>"Z","И"=>"I","Й"=>"JJ","К"=>"K","Л"=>"L",
   "М"=>"M","Н"=>"N","О"=>"O","П"=>"P","Р"=>"R",
   "С"=>"S","Т"=>"T","У"=>"U","Ф"=>"F","Х"=>"KH",
   "Ц"=>"C","Ч"=>"CH","Ш"=>"SH","Щ"=>"SHH","Ъ"=>"'",
   "Ы"=>"Y","Ь"=>"","Э"=>"EH","Ю"=>"YU","Я"=>"YA",
   "а"=>"a","б"=>"b","в"=>"v","г"=>"g","д"=>"d",
   "е"=>"e","ё"=>"jo","ж"=>"zh",
   "з"=>"z","и"=>"i","й"=>"jj","к"=>"k","л"=>"l",
   "м"=>"m","н"=>"n","о"=>"o","п"=>"p","р"=>"r",
   "с"=>"s","т"=>"t","у"=>"u","ф"=>"f","х"=>"kh",
   "ц"=>"c","ч"=>"ch","ш"=>"sh","щ"=>"shh","ъ"=>"",
   "ы"=>"y","ь"=>"","э"=>"eh","ю"=>"yu","я"=>"ya"
  );
 
$iso = array(
   "Є"=>"YE","І"=>"I","Ѓ"=>"G","і"=>"i","№"=>"#","є"=>"ye","ѓ"=>"g",
   "А"=>"A","Б"=>"B","В"=>"V","Г"=>"G","Д"=>"D",
   "Е"=>"E","Ё"=>"YO","Ж"=>"ZH",
   "З"=>"Z","И"=>"I","Й"=>"J","К"=>"K","Л"=>"L",
   "М"=>"M","Н"=>"N","О"=>"O","П"=>"P","Р"=>"R",
   "С"=>"S","Т"=>"T","У"=>"U","Ф"=>"F","Х"=>"X",
   "Ц"=>"C","Ч"=>"CH","Ш"=>"SH","Щ"=>"SHH","Ъ"=>"'",
   "Ы"=>"Y","Ь"=>"","Э"=>"E","Ю"=>"YU","Я"=>"YA",
   "а"=>"a","б"=>"b","в"=>"v","г"=>"g","д"=>"d",
   "е"=>"e","ё"=>"yo","ж"=>"zh",
   "з"=>"z","и"=>"i","й"=>"j","к"=>"k","л"=>"l",
   "м"=>"m","н"=>"n","о"=>"o","п"=>"p","р"=>"r",
   "с"=>"s","т"=>"t","у"=>"u","ф"=>"f","х"=>"x",
   "ц"=>"c","ч"=>"ch","ш"=>"sh","щ"=>"shh","ъ"=>"",
   "ы"=>"y","ь"=>"","э"=>"e","ю"=>"yu","я"=>"ya"
  );
 
if($alias == "") {
switch ($rtl_standard) {
    case 'off':
        $alias = $pagetitle;
        break;      
    case 'gost':
        $alias = strtr($pagetitle, $gost);
        break;
    default: 
        $alias = strtr($pagetitle, $iso);
        break;
}
 
$alias = strtolower( $alias );
$alias = preg_replace('/&.+?;/', '', $alias); // kill entities
$alias = str_replace( '_', '-', $alias );
$alias = preg_replace('/[^a-z0-9\s-.]/', '', $alias);
$alias = preg_replace('/\s+/', '-', $alias);
$alias = preg_replace('|-+|', '-', $alias);
$alias = trim($alias, '-');
 
}