Validation does not work for fields in group

Hello,

When fields are in a group, the validation does not works.
For example, in the metabox below :
– the litte red star displays next “Légende et crédits de la vidéo” (that’s ok)
– the post can be publish even when “vm_video_legend” is empty
– “vm_video_link” displays the english validation message “Please enter a valid URL.” instead of mine “Ce champ doit être une url valide”.

$meta_boxes[] = array(
    'title'      => __( 'La résidence', 'vm' ),
    'post_types' => array( 'residence' ),
    'context'    => 'normal',
    'priority'   => 'high',
    'id'         => 'vm_residence',
    'fields' => array(
        array(
            'name'    => __( 'Vidéo', 'vm' ),
            'id'      => 'vm_video_group',
            'type'    => 'group',
            'fields' => array(
                array(
                    'name'    => __( 'Lien de la vidéo (Youtube, Vimeo)', 'vm' ),
                    'id'      => 'vm_video_link',
                    'type'    => 'oembed',
                ),
                array(
                    'name'    => __( 'Légende et crédits de la vidéo', 'vm' ),
                    'id'      => 'vm_video_legend',
                    'type'    => 'text',
                ),

            ),
        ),
    ),
    'validation' => array(
        'rules' => array(
            'vm_video_group' => array(
                "vm_video_link" => array(
                    'url'  => true,
                ),
                "vm_video_legend" => array(
                    'required'  => true,
                ),
            ),
        ),
        'messages' => array(
            'vm_video_group' => array(
                "vm_video_link" => array(
                    'url'  => __( 'Ce champ doit être une url valide', 'vm' ),
                ),
                "vm_video_legend" => array(
                    'required'  => __( 'Ce champ est requis', 'vm' ),
                ),
            ),
        ),
    ),
);

I also tried to define validation rules and messages like below with no success

<?php 

'validation' => array(
    'rules' => array(
        'vm_video_group' => array(
            "vm_video_link" => array(
                'url'  => true,
            ),
            "vm_video_legend" => array(
                'required'  => true,
            ),
        ),
    ),
    'messages' => array(
        'vm_video_group' => array(
            "vm_video_link" => array(
                'url'  => __( 'Ce champ doit être une url valide', 'vm' ),
            ),
            "vm_video_legend" => array(
                'required'  => __( 'Ce champ est requis', 'vm' ),
            ),
        ),
    ),
),

?>

Can you fix this please ?

Regards,