function mlp_navigation_with_login()

mlp_navigation_with_login.php

<?php

// copy from here

/**
 * Create a navigation like: DE | EN | RU | Log in
 *
 * @return string
 */
function mlp_navigation_with_login()
{
	$linked = (array) mlp_get_interlinked_permalinks();
	$items  = $login = array ();

	$links[] = array (
		'permalink' => '',
		'lang'      => mlp_get_current_blog_language()
	);
	
	$links = array_merge( $links, $linked );

	// add log in/out link
	if ( ! is_user_logged_in() ) {
		$login['permalink'] = wp_login_url( $_SERVER['REQUEST_URI'] );
		$login['text']      = __( 'Log in' );
	}
	else {
		$login['permalink'] = wp_logout_url( $_SERVER['REQUEST_URI'] );
		$login['text']      = __( 'Log out' );
	}

	$links[] = $login;

	// format the items
	foreach ( $links as $link ) {
		// log in/out
		if ( isset ( $link['text'] ) )
			$text = $link['text'];
		else
			$text = strtoupper( strtok( $link['lang'], '_' ) );

		$hreflang = '';

		if ( ! empty ( $link['lang'] ) )
			$hreflang = 'hreflang="' . esc_attr( $link['lang'] ) . '"';

		$items[] = sprintf(
			'<a href="%1$s" rel="nofollow" %2$s>%3$s</a>',
			esc_url( $link['permalink'] ),
			$hreflang,
			$text
		);
	}

	return '<p class="lang-login-nav">' . join( ' | ', $items ) . '</p>';
}

Gives an notice if the linked permalinks array $links is empty. If you array merge these 2 array it doesn't have an empty array in the loop.
See https://gist.github.com/jmslbam/c2d9240e76654cd27481/revisions#diff-6a0f70159046c3eb1bd4a4a7b317eed4L12

Thanks btw!