The following code will preserve the structure of original $lang array:
$find = 'value1';
$result = array_filter($lang, function($rec) use ($find) {
return in_array($find, $rec);
});
Where $result will be:
array (
'lbl_mylabel1' =>
array (
'key1' => 'value1',
),
'lbl_mylabel2' =>
array (
'key2' => 'value1',
),
'lbl_mylabel3' =>
array (
'key3' => 'value1',
),
)