gistfile1.php

<?php
/*

Handles URL Rewriting in WordPress 3.0 like this:

fastigheter-spanien/X -> property/X&lang=sv
fastigheter-usa/X -> property/X&lang=sv
properties-spain/X -> property/X&lang=en
properties-usa/X -> property/X&lang=en

Answer for: http://wpquestions.com/question/show/id/694

By: Mike Schinkel

Copy this to your theme's functions.php file or put the code in a plugin. 
Be sure to rename the "my_*()" functions to something unique that makes 
sense in your sites context.

*/
add_action('init', 'my_init');
function my_init() {
	global $wp,$wp_rewrite;
	$wp->add_query_var('lang');
	$wp_rewrite->add_rewrite_tag('%lang%','([^/]+)','lang=');
	$wp_rewrite->add_permastruct('fastigheter', 'fastigheter-%lang%/%property%');
	$wp_rewrite->add_permastruct('properties',  'properties-%lang%/%property%');

	register_post_type('property',
		array(
			'label'          => 'Property',
			'public'          => true,
			'show_ui'         => true,
			'query_var'       => 'property',
			'rewrite'         => array('slug' => 'property'),
			'hierarchical'    => true,
			'supports'        => array(
				'title',
				'editor',
				'excerpts',
				'custom-fields',
				'page-attributes',
				'thumbnail'
			),
		)
	);

	/*
	 * The line that follows should be deleted and go in a plugin activation hook
	 * or you can just update permalinks in the admin once (after adding this
	 * code) by going here:
	 *
	 *    http://example.com/wp-admin/options-permalink.php
	 *
	 * (replace example.com above with your domain)
	 *
	 */
	$wp_rewrite->flush_rules(true);
}
add_filter('request', 'my_request');
function my_request($request) {
	if (isset($request['lang']))
		switch ($request['lang']) {
			case 'spanien':
			case 'spain':
				$request['lang'] = 'sv';
				break;
			case 'usa':
			default:
				$request['lang'] = 'en';
		}
	return $request;
}
function get_property_lang() {
	global $wp_query;
	return (isset($wp_query->query_vars['lang']) ? $wp_query->query_vars['lang'] : '');
}