Translate Trait in OctoberCMS v4

Need Help
#1

For a brand new site, I’m trying to understand the core Translate logic without using the Rainlab Translate plugin (the logic seems similar)…

I have a multisite (locales ‘en’ and ‘fr’) and I get an error when I use the Translatable trait in my Custom Setting Model when I save the attribute in the translation widget.

Call to undefined method System\Controllers\Settings::formBeforeSave()

My class :

<?php namespace Acme\Demo\Models;

class MySetting extends \System\Models\SettingModel
{
    use \October\Rain\Database\Traits\MultisiteGroup;
    use \October\Rain\Database\Traits\Translatable;

    public $translatable = [
        'about_description',
        'focus_description',
    ];

    (...)

Also, is Translation of CMS Pages (title, URL, SEO, etc.) implemented?

Thanks