Delete a language.
$langcode: Language code of the language to be deleted.
TRUE if language is successfully deleted. Otherwise FALSE.
function language_delete($langcode) {
  $languages = language_list(Language::STATE_ALL);
  if (isset($languages[$langcode]) && !$languages[$langcode]->locked) {
    $language = $languages[$langcode];
    module_invoke_all('language_delete', $language);
    // Remove the language.
    db_delete('language')
      ->condition('langcode', $language->langcode)
      ->execute();
    language_update_count();
    // Update weight of locked system languages.
    language_update_locked_weights();
    drupal_static_reset('language_list');
    $t_args = array(
      '%language' => $language->name,
      '%langcode' => $language->langcode,
    );
    watchdog('language', 'The %language (%langcode) language has been removed.', $t_args);
    return TRUE;
  }
  return FALSE;
}