language_header.module

<?php
/**
 * @file
 * Language header module.
 */

define('LANGUAGE_HEADER_HEADER', 'X-Accept-Language');
define('LANGUAGE_HEADER_PROVIDER', 'language_header');
define('LANGUAGE_HEADER_CONFIG_PATH', 'admin/config/regional/language/configure/header');

/**
 * Implements hook_menu().
 */
function language_header_menu() {
  return array(
    LANGUAGE_HEADER_CONFIG_PATH => array(
      'type' => MENU_VISIBLE_IN_BREADCRUMB,
      'file' => 'language_header.admin.inc',
      'title' => 'Configure HTTP header language negotiation',
      'page callback' => 'drupal_get_form',
      'page arguments' => array('language_header_admin_form'),
      'access arguments' => array('administer languages'),
    ),
  );
}

/**
 * Implements hook_language_negotiation_info().
 */
function language_header_language_negotiation_info() {
  return array(
    LANGUAGE_HEADER_PROVIDER => array(
      'name' => t('HTTP header'),
      'weight' => -5,
      'config' => LANGUAGE_HEADER_CONFIG_PATH,
      'file' => drupal_get_path('module', 'language_header') . '/language_header.module',
      'description' => t('Determine the language from HTTP header'),
      'callbacks' => array(
        'language' => 'language_header_language',
      ),
    ),
  );
}

/**
 * Identify language from a custom HTTP header.
 *
 * @see language_initialize()
 * @see language_provider_invoke()
 *
 * @param \stdClass[] $languages
 *   An associative array of enabled languages.
 *
 * @return string|bool
 *   Valid language code or FALSE if header is not set or language
 *   code is not valid. FALSE needs to be returned to allow other
 *   language providers to determine the language code.
 */
function language_header_language(array $languages) {
  $header = language_header_name();

  return isset($_SERVER[$header], $languages[$_SERVER[$header]]) ? $_SERVER[$header] : FALSE;
}

/**
 * Returns the name of HTTP header where the language code should be set.
 *
 * @return string
 *   Name of HTTP header.
 */
function language_header_name() {
  return 'HTTP_' . str_replace('-', '_', strtoupper(
    variable_get('language_header_header', LANGUAGE_HEADER_HEADER)
  ));
}