<?php
 $regularArray = array(      
        array( "label" => "Hello World", "value" => 1 ),
        array( "label" => "Hej Världen", "value" => 2 )
    );
    $regularArray[1]['label'] = utf8_encode( $regularArray[1]['label']);
    echo $jsonArray = json_encode( $regularArray );
    $data = json_decode($jsonArray, true);
    $data[1]['label'] = utf8_decode($data[1]['label']);
    print_r($data);

?>

[{"label":"Hello World","value":1},{"label":"Hej V\u00c3\u00a4rlden","value":2}]Array
(
    [0] => Array
        (
            [label] => Hello World
            [value] => 1
        )

    [1] => Array
        (
            [label] => Hej Världen
            [value] => 2
        )

)