add_language_slug_to_blog_name_in_admin_bar.php

<?php
/**
 * Plugin Name: Cross Media Cloud | Add language slug to blog name in admin bar
 * Description:	Show the blog language within the drop down of sites within the admin bar
 * Version:     1.0
 * Author:      Cross Media Cloud
 * Author URI:  https://www.cross-media-cloud.de
 * License:     GNU General Public License v2 or later
 * License URI: http://www.gnu.org/licenses/gpl-2.0.html
 */

 if( ! defined( 'ABSPATH' ) )
	exit;

add_action('wp_before_admin_bar_render', 'add_language_to_blog_name');
function add_language_to_blog_name( $wp_admin_bar ) {

	global $wp_admin_bar;

	$wp_admin_bar->add_menu( array(
		'id'    => 'site-name',
		'title' => get_bloginfo( 'name' ) . ' | ' . get_bloginfo( 'language' ),
	) );

}

add_action( 'wp_before_admin_bar_render', 'f711_tweaked_admin_bar' );
function f711_tweaked_admin_bar() {

	global $wp_admin_bar;
	$elements = $wp_admin_bar->get_nodes();
	foreach( $elements as $element ) {

		if ( $element->parent == 'my-sites-list' ) {

			// reduce the adminbar Id to the blog ID
			$idinteger = str_replace( 'blog-', '', $element->id );

			// Switch to the Blog, get the language option. If empty, it's English
			switch_to_blog( $idinteger );
			if ( get_option( 'WPLANG' ) != "" ) {
				$language = get_option( 'WPLANG' );
			} else {
				$language = 'en_EN';
			}
			//set the new title for the Admin Menu
			$newtitle = $element->title . ' | ' . $language;
			restore_current_blog();

			// define new menu element
			$args = array(
				'title'     => $newtitle,
				'id'        => $element->id,
				'parent'    => $element->parent,
				'href'      => $element->href,
			);
			// remove the old one
			$wp_admin_bar->remove_node( $element->id );
			// add the new one right afterwards.
			$wp_admin_bar->add_node( $args );

		}

	}

}