[eluser]marcoss[/eluser]
You got that wrong, what you want to change is the language folder, you do that in config.php, where you have this,
Code:
$config['language'] = 'english';
change it to slovak,
Code:
$config['language'] = 'slovak';
that will tell codeigniter to look for error files on that folder, if you then need an
extra language file (ie, not the system ones) you loaded in the autoload.php file or manually when you need them.