Meta query with compare by more than 2 fields

Question

i have 5 sets of meta boxes in some custom postype. So.. i know how to compare two meta box values...

Example:

'meta_query'        => array(
    'relation'  => 'AND',
    array(
        'key'     => THEME_PREF.'source_lang_1',
        'value'   => $sourceLang,
        'compare' => '='
    ),
    array(
        'key'     => THEME_PREF.'target_lang_1',
        'value'   => $targetLang,
        'compare' => '='
    ),
),

But...
what if i need to check 4 fields - the verification isnt true..
meaning it doesnt returnes only the right results
only "posts" that answer both conditions.

$transargs = array(
    'post_type'         =>  'translators',
    'orderby'           =>  'date',
    'order'             =>  'DESC',
    'posts_per_page'    =>  -1,
    'meta_query'        => array(
        'relation' => 'OR',
        array(
            'relation' => 'AND',
            array(
                'key'       =>  THEME_PREF.'source_lang_1',
                'value'     =>  $sourceLang,
                'compare'   =>  '='
            ),
            array(
                'key'       =>  THEME_PREF.'target_lang_1',
                'value'     =>  $targetLang,
                'compare'   =>  '='
            )
        ),
        array(
            'relation' => 'AND',
            array(
                'key'       =>  THEME_PREF.'source_lang_2',
                'value'     =>  $sourceLang,
                'compare'   =>  '='
            ),
            array(
                'key'       =>  THEME_PREF.'target_lang_2',
                'value'     =>  $targetLang,
                'compare'   =>  '='
            )
        ),
    )   
);
$trns_query = new WP_Query($transargs);

To elaborate
i get a lot of results where the first condition of each meta query is met but not the second one and thus the relation and

Example:
$sourceLang = 1;
$targetLang = 2;

i might also get
(which is not good... the AND doesnt work?)...
result that equals $sourcelang(1) / targetLang(5)

Answer 1

Nested relations among subset of meta queries are possible on WP 4.1 that is planned to be releaded next coming December 10, 2014. See trac ticket.

So wait a few days or use the beta version.