MultilingualPress Add on to filter non public sites.

mlp-filter-site.php

<?php # -*- coding: utf-8 -*-
/**
 * Plugin Name: MultilingualPress Add on to hide Non-public Sites
 * Description: This is a simple add-on for the MultilingualPress plugin to hide non-public sites (i.e., languages) from translation lists such as the Language Switcher widget or the Quicklinks.
 * Author:      Inpsyde GmbH
 * Author URI:  http://inpsyde.com
 * Version:     2015-09-16
 * License:     GPLv2+
 * Network:     true
 */

defined( 'ABSPATH' ) or die();

add_filter( 'mlp_translations', 'mlp_hide_non_public_sites' );

/**
 * Hide translations for non-public sites.
 *
 * @param Mlp_Translation[] $translations Translation objects.
 *
 * @return Mlp_Translation[]
 */
function mlp_hide_non_public_sites( array $translations ) {

	foreach ( array_keys( $translations ) as $site_id ) {
		if ( ! get_blog_option( $site_id, 'blog_public' ) ) {
			unset( $translations[ $site_id ] );
		}
	}

	return $translations;
}

The add on was created for this support topic, maybe heloful for other users about background and goal. https://wordpress.org/support/topic/hide-a-non-plublic-site-from-switcher