Function for loading a textdomain into a WordPress theme.

WordPress: Theme Textdomain

/**
 * Makes theme available for the built-in localization
 **/
function xld_localization_support(){

     $locale = get_locale();

     load_theme_textdomain( 'textdomain', get_template_directory() . '/languages' );
     $locale_file = get_template_directory() . "/languages/$locale.php";

     if ( is_readable( $locale_file ) ){
          require_once( $locale_file );
     }

}

add_action( 'init', 'xld_localization_support' );