Error in accents and accents Codeigniter Angular

When returning a result in Codeigniter and Angular the accents become

contrase\u00f1a
        ^^^^^^

How can I solve the error?

Code PHP Codeigniter

$this->output->set_content_type('application/json');
$this->output->set_output(json_encode($response));

Angular Code

$scope.ErrorMessage = data.message;

I have the following code:

function getMessage($key){
    $file = parse_ini_file('application/messages.properties');
    return $file[$key]; 
}