app.php

<?php
class App {
  /**
   * Translates string.
   *  Examples:
   *      echo \App::translate('Páginas');
   *      > Pages
   *      echo \App::translate('Oi %s, é Domingo! Seu e-mail %s está cheio', 'Dev', 'lol@dev.us');
   *      > Hi Dev, is Sunday! Your mail lol@dev.us is full
   *      echo \App::translate('Boa tarde');
   *      > Boa tarde <= hasn't been translated because they do not have a translation for this word
   *      echo \App::translate('Ontem');
   *      > Yesterday
   * 
   * @param string $text text to translate.
   * @param string replaces
   * @return string
   * @todo This is experimental
   */
  public static function translate($text)
  { 
      $replace = func_get_args();
      unset($replace[0]);
      
      $ci =& get_instance();
      
      $session = $ci->auth->get_session();
      $lang = $session['user_idioma'];
      
      if ($lang != LANGUAGE_DEFAULT) {
          $ci->lang->load('app', LANGUAGE_DEFAULT);
          $key = array_search($text, $ci->lang->language);
          $ci->lang->load('app', $lang);
          if ($ci->lang->line($key))
              $text = $ci->lang->line($key);
      }

      if ($replace)
          $text = vsprintf($text, $replace);
      
      return $text;
  }
}

lang_br.php

<?php
$lang['pages'] = 'Páginas';
$lang['saudation'] = 'Oi %s, é Domingo! Seu e-mail %s está cheio';
$lang['random_index'] = 'Ontem';

lang_en.php

<?php
$lang['pages'] = 'Pages';
$lang['saudation'] = 'Hi %s, is Sunday! Your mail %s is full';
$lang['random_index'] = 'Yesterday';