WordPress Set Locale Simple Plugin

<?php
/*
Plugin Name: Set Locale
Plugin URI: http://yoursite.tld
Description: Sets the locale
Author: Johannes Pilkahn
Version: 1.0
Author URI: http://tramprennen.org
*/

function sl_current_lang() {
    $sl_uri = $_SERVER["REQUEST_URI"];
    $sl_lang = array_pop( explode( '/',  $sl_uri ) );

    return $sl_lang;
}

function sl_set_locale() {

    if( sl_current_lang() == 'en' ) {
        define( 'WPLANG', 'en_US' );
    } else {
        define( 'WPLANG', 'el_GR' );
    }
}

sl_set_locale();

?>