Setting default language in config

Have you copied the appropriate language folders from https://github.com/bcit-ci/codeigniter3-translations into your application/language folder?

Code:

$this->lang->load('error_messages', 'english');
echo $this->lang->line('error1'); // looks in system/language/english/error_messages_lang.php
$this->lang->load('error_messages', 'polish');
echo $this->lang->line('error1'); // looks in application/language/polish/error_messages_lang.php