Naturally sort an associative subarray by its keys in a descending direction

I'm trying to sort an array by the value of a sub-key in DESC order but I'm stuck. I've could make it with ksort but it was in ascending order.

Here's my array:

$array_by_lang = array(
    [no] => array(
        [3-1] => array(//some informations),
        [3-10] => array(//informations),
        [3-7] => array(//informations),
        [5-1] => array(//informations)
    )
)

What I want to obtain is something like:

$array_by_lang = array(
    [no] => array(
        [5-1] => array(//informations),
        [3-10] => array(//some informations),
        [3-7] => array(//informations),
        [3-1] => array(//informations)
    )
)

I think, you need "reversing natural sort by key". Just with array_multisort and array_reverse (see also natsort):

    $array_by_lang = array(
        'no' => array(
            '3-1'  => array('info_1'),
            '3-10' => array('info_2'),
            '3-7'  => array('info_3'),
            '5-1'  => array('info_4'),
        )
    );


    array_multisort(array_keys($array_by_lang['no']),SORT_NATURAL, $array_by_lang['no']);
    $array_by_lang['no'] = array_reverse($array_by_lang['no']); // reverse natural order - "DESC"
    var_dump($array_by_lang);

Output

array(1) {
  ["no"]=>
    array(4) {
    ["5-1"]=>
      array(1) {
        [0]=>
        string(6) "info_4"
    }
    ["3-10"]=>
      array(1) {
        [0]=>
        string(6) "info_2"
    }
    ["3-7"]=>
      array(1) {
        [0]=>
        string(6) "info_3"
    }
    ["3-1"]=>
      array(1) {
       [0]=>
       string(6) "info_1"
    }
   }
}