Validation field label language

Hi, that part haven't made it to the official user guide. But here's what it says in the development branch:

To use translated strings from language files, we can simply use the dot syntax. Let’s say we have a file with translations located here: app/Languages/en/Rules.php. We can simply use the language lines defined in this file, like this:

PHP Code:

$validation->setRules([
        'username' => [
            'label'  => 'Rules.username',
            'rules'  => 'required|is_unique[users.username]',
            'errors' => [
                'required' => 'Rules.username.required'
            ]
        ],
        'password' => [
            'label'  => 'Rules.password',
            'rules'  => 'required|min_length[10]',
            'errors' => [
                'min_length' => 'Rules.password.min_length'
            ]
        ]
    ]
); 


I did this in Config/Validation.php

PHP Code:

public $updateSettings  =   [
                'site_name'             =>      ['label' => 'App.site_name', 'rules'  =>  'required'],
        ]; 


But still give site_name, not what site_name in App language file.