WordPress plugin to deal with language cookies. Create one page for each language. Then a menu with them. Configure the arguments in the plugin file. Than do your thing in your theme with $_COOKIE[cookie_name].

language-cookie-wpse-113662.php

<?php

/**
 * Plugin Name: Language Cookie
 * Plugin URI: http://wordpress.stackexchange.com/q/113662/12615
 * Description: Create one page for each language. Then a menu with them. Configure the arguments in the plugin file. Than do your thing in your theme with $_COOKIE[cookie_name].
 * Version: 0.1
 * Requires: PHP 5.3+
 * Author: Rodolfo Buaiz 
 * Author URI: http://www.rodbuaiz.com
 */

add_action( 'plugins_loaded', function() {
	$args = array(
		# Pair of cookie value => page-slug or page-id
		'translation_pages'	 => array(
			'en' => 'english',
			'ar' => 'arabic',
			'pt' => 5594
		),
		# Site where plugin is running
		'domain'			 => 'plugins.dev',
		# Name of the croissant stored in your system
		'cookie_name'		 => 'my-site-language',
		# Appended to the language menus, used to get back to the same origin page. 
		# # Ex:http:example.com/somepage?lingo=http%3A%2F%2Fexample.com%2Fsomepage
		'query_var'			 => 'lingo',
		# Check for oscilations in code
		'debug'				 => false,
	);
	new B5F_Cookie_Translate( $args );
} );

class B5F_Cookie_Translate
{
	/**
	 * Holds the plugin options
	 *
	 * @var array
	 */
	protected $params;

	/**
	 * Array of cookie names
	 *
	 * @var array
	 */
	protected $cookies;

	/**
	 * Array of page names (aligned with $cookies)
	 *
	 * @var array
	 */
	protected $lingo_pages;

	/**
	 * Set up basic information
	 * 
	 * @param  array $options
	 * @return void
	 */
	public function __construct( array $options )
	{
		$defaults = array(
			'translation_pages'	 => array( ),
			'debug'				 => false,
			'domain'			 => 'example.com',
			'cookie_name'		 => 'hello_cookie',
			'query_var'			 => 'change_lenguage',
		);

		$this->params = array_merge( $defaults, $options );
		$this->cookies = array_keys( $this->params['translation_pages'] );
		$this->lingo_pages = array_values( $this->params['translation_pages'] );

		add_filter( 'wp_get_nav_menu_items', array( $this, 'nav_items' ), 11, 3 );
		add_action( 'template_redirect', array( $this, 'redirect' ) );
		if( $this->params['debug'] && !is_admin() )
			add_filter( 'the_content', array( $this, 'debug' ) );
	}


	/**
	 * Add query var to translation menu items
	 * 
	 * @param  object $items
	 * @param  object $menu
	 * @param  array $args
	 * @return object
	 */
	public function nav_items( $items, $menu, $args )
	{
		if( is_admin() )
			return $items;

		# http://kovshenin.com/2012/current-url-in-wordpress/
		global $wp;
		$current_url = urlencode( home_url( $wp->request ) );

		# Build array with Page IDs
		$object_ids = array( );
		foreach( $this->params['translation_pages'] as $page )
		{
			$get_page = is_int( $page ) ? get_page( $page ) : get_page_by_path( $page );
			if( $get_page )
				$object_ids[] = $get_page->ID;
		}

		# Build return array
		$new_items = array( );
		foreach( $items as $item )
		{
			# object_id is the only reference to the original item
			if( !empty( $item->url ) && in_array( $item->object_id, $object_ids ) )
				$item->url = $item->url . "?{$this->params['query_var']}=$current_url";

			$new_items[] = $item;
		}
		return $new_items;
	}


	/**
	 * Template redirect action
	 * 
	 * @return void
	 */
	public function redirect()
	{
		$c_name = $this->params['cookie_name'];

		# No cookie set, let's do it
		if( !isset( $_COOKIE[$c_name] ) )
			$this->set_cookie( $this->cookies[0] );

		# One of our pages, change cookie
		if( is_page( $this->lingo_pages ) )
		{
			$q_var = $this->params['query_var'];
			$goto = isset( $_GET[$q_var] ) ? esc_url( urldecode( $_GET[$q_var] ) ) : '';

			foreach( $this->params['translation_pages'] as $lingo => $page )
			{
				if( is_page( $page ) && $_COOKIE[$c_name] != $lingo )
					$this->set_cookie( $lingo );
			}

			$this->do_redirect( $goto );
		}
	}


	/**
	 * Set cookie
	 * 
	 * @param  string $lingo Cookie value
	 * @return void
	 */
	private function set_cookie( $lingo )
	{
		$domain = '.' . $this->params['domain'];
		setcookie( $this->params['cookie_name'], $lingo, time() + 3600 * 24 * 365 * 3, '/', $domain );
	}


	/**
	 * Redirect browser
	 * 
	 * @param  string $where URL for redirection
	 * @return void
	 */
	private function do_redirect( $where = '' )
	{
		$where = empty( $where ) ? home_url() : $where;
		wp_redirect( $where );
		exit();
	}


	/**
	 * Enable printing of the cookie name with the_content
	 * 
	 * @param  string $content
	 * @return string
	 */
	public function debug( $content )
	{
		$text = isset( $_COOKIE[$this->params['cookie_name']] ) ? $_COOKIE[$this->params['cookie_name']] : 'Cookie not set';
		return "<h1>$text</h1>$content";
	}


}