Drupal language custom provider

module.locale.inc

<?php

/**
 * @file
 * Handles localization for module.
 */


/**
 * Language callback for selecting the active language.
 */
function MODULE_language_provider_callback($languages) {
  include_once DRUPAL_ROOT . '/includes/locale.inc';

  list($language, $_GET['q']) = language_url_split_prefix(isset($_GET['q']) ? $_GET['q'] : NULL, $languages);

  if ($language === FALSE && isset($languages['pt-pt'])) {
    return $languages['pt-pt']->language;
  }

  return locale_language_from_url($languages);
}

/**
 * Language callback for language switcher.
 */
function MODULE_language_switcher_callback($type, $path) {
  return locale_language_switcher_url($type, $path);
}

/**
 * Language callback for URL rewrite.
 */
function MODULE_language_url_rewrite_callback(&$path, &$options) {
  locale_language_url_rewrite_url($path, $options);

  if (empty($options['language'])) {
    return;
  }

  switch ($options['language']->language) {
    case 'pt-pt':
      $options['prefix'] = '';
      break;

    default:
      $options['prefix'] = $options['language']->language . '/';
      break;
  }
}