Translation for a WordPress Child Theme

child-functions.php

<?php
/*
 CHILD THEME functions.php file
 */
if ( !function_exists('child_localization')) {
  function child_localization() {
    load_child_theme_textdomain('child_text_domain',  get_stylesheet_directory() . '/lang');
  }
  add_action('after_setup_theme', 'child_localization');
}

// useful debug tool : http://marketpress.com/product/debug-translations/
// thank you @jennybeaumont ;)

parent-functions.php

<?php
/*
 PARENT THEME functions.php file
 */
if ( !function_exists('parent_localization')) {
  function parent_localization() {
    load_theme_textdomain('parent_text_domain',  get_template_directory() . '/languages');
  }
  add_action('after_setup_theme', 'parent_localization');
}