materio-base-d7/sites/all/modules/sandbox/search_api_base_language/search_api_base_language.module

<?php

/**
* Implements hook_search_api_alter_callback_info
**/
function search_api_base_language_search_api_alter_callback_info() {
  $callbacks['base_language'] = array(
    'name' => t('Base language'),
    'description' => t('The language to use when indexing content.'),
    'class' => 'SearchAPIBaseLanguage',
    'weight' => 100,
  );
  return $callbacks;
}