Can't do remote submission to LDO server

A member from zh-hant group reported a remote submission problem.
I've done a test with http://drupal.org/project/l10n_install and self installation. And got following error message from the server:

Translation rejected by http://localize.drupal.org. Reason: Not allowed to submit translations in this language.

Here is my self debug message from l10n_clent:

/**
 * Submit translation to the server.
 */
function l10n_client_submit_translation($langcode, $source, $translation, $user_key, $user_token) {
  $server_uid = current(split(':', $user_key));
  $signature = md5($user_key . $langcode . $source . $translation . $user_token);
  $server_url = variable_get('l10n_client_server', 'http://localize.drupal.org');

  $response = xmlrpc(
    $server_url .'/xmlrpc.php',
    array('l10n.submit.translation' => array(
      $langcode,
      $source,
      $translation,
      (int)$server_uid,
      $user_token,
      $signature
    ))
  );

  watchdog('l10n_client', print_r(array(
    $langcode,
    $source,
    $translation,
    (int)$server_uid,
    $user_token,
    $signature
  ), 1));

Result:
Array ( [0] => zh-hant [1] => Content [2] => 內容deeeeeeeeeeeeeeeeee [3] => 2740 [4] => fb0cfa8eadd6501467a1b3451c04d707 [5] => 5e421943391b6182808c7c9e3eb7ad19 )

( I'm the admin of zh-hant group so I bet not the permission issue. )