CristianOspina

Mmm never mind, I solved:

add_action('save_post', 'save_other_video_thumbnail', 100, 1);
function save_other_video_thumbnail($post_id) {
$postdata = get_postdata($post_id);
	if ($postdata['post_status'] == 'future') {
		get_video_thumbnail($post_id);
	}
}

This is a part of the SQL:
AND (wp_postmeta.meta_key = 'personas' OR (mt1.meta_key = 'idioma' AND CAST(mt1.meta_value AS CHAR) = '') OR (mt2.meta_key = 'idioma_2' AND CAST(mt2.meta_value AS CHAR) = '') )
apparently what happens is that the order meta_key is added to meta_query then the order does not affected, being ordained by default:
GROUP BY wp_posts.ID ORDER BY wp_posts.post_date desc LIMIT 0, 15

Then, there is another way to sort by meta_key without combining with meta_query?

This is the same problem on StackOverflow. But I can not get my code works… Help please!