In Codeigniter 3 I use alpha to validate form for only letters
$this->form_validation->set_rules('firstname', 'FirstName', 'trim|required|alpha',
array('required' => 'please refill', 'alpha' => 'don't want integer')
);
but the problem is the Thai Language letter is not work T_T(it's work only for English letter). I have already put a meta charset utf-8 on head section, but it's not work too. How should I do?