Wikipedia_Entry_Inserter.php

<?php
/**
 *Plugin Name: Wikipedia_Entry_Inserter
 *Version:     0.1
 *Plugin URI:  http://argcandargv.com
 *Description:  insert wikipedia entry with [wiki] and [/wiki]
 *Author:      Yu Jing
 *Author URI:  http://argcandargv.com/
 */

function Wikipedia_Entry_Inserter($outer){
	if(!is_singular()){ return $outer; }
	$outer = preg_replace('/\[wiki\](.+?)\[\/wiki\]/','<a href="//en.wikipedia.org/wiki/$1" rel="nofollow" title="$1" target="_blank">$1</a>', $outer);
	$outer = preg_replace('/\[wiki:zh\](.+?)\[\/wiki:zh\]/','<a href="//zh.wikipedia.org/wiki/$1" rel="nofollow" title="$1" target="_blank">$1</a>', $outer);
	return $outer;
}

add_filter('the_content', 'Wikipedia_Entry_Inserter');

?>