Change array key without changing order

Something like this may also work:

$langs = array("EN" => "English", 
        "ZH" => "Chinese", 
        "DA" => "Danish",
        "NL" => "Dutch", 
        "FI" => "Finnish", 
        "FR" => "French",
        "DE" => "German");
$json = str_replace('"EN":', '"en":', json_encode($langs));
print_r(json_decode($json, true));

OUTPUT:

Array
(
    [en] => English
    [ZH] => Chinese
    [DA] => Danish
    [NL] => Dutch
    [FI] => Finnish
    [FR] => French
    [DE] => German
)

Tested and works :)

function replace_key($array, $old_key, $new_key) {
    $keys = array_keys($array);
    if (false === $index = array_search($old_key, $keys, true)) {
        throw new Exception(sprintf('Key "%s" does not exist', $old_key));
    }
    $keys[$index] = $new_key;
    return array_combine($keys, array_values($array));
}

$array = [ 'a' => '1', 'b' => '2', 'c' => '3' ];    
$new_array = replace_key($array, 'b', 'e');