Showing different pages depending on a cookie value

Question

You could hook into the template redirect function.

function my_page_template_redirect() {

    if ( isset( $_COOKIE["myCookie"] ) ) {
        if( $_COOKIE["myCookie"] == "en" ) {            
            wp_redirect( 'you path' );
            exit;
        }
    }

}
add_action( 'template_redirect', 'my_page_template_redirect' );

And you could better use wp_redirect() function to redirect inside WordPress.