Change Default Language

For change the default language, I change in file: astpp/application/libraries/locale.php
the line:
function set_lang($lang = FALSE) {
$current_locale = $this->CI->session->userdata ( 'user_language' );
if (empty ( $current_locale )) {
$current_locale = 'en_US';

to

function set_lang($lang = FALSE) {
$current_locale = $this->CI->session->userdata ( 'user_language' );
if (empty ( $current_locale )) {
$current_locale = 'pt_BR';

This works fine. But when I use the footer flags to change language to English, the language don't change to english. Change to French and Spanish, but to english no.

I thinks is something with url:
/application/modules/user/language/' . $lang . '/LC_MESSAGES/messages.mo

In thie folder /application/modules/user/language/ don't have folder en_US.