[Availability Subscriber] - User Language

[mamontani]

Is your feature request related to a problem? Please describe.

When the customer register for the availability notification, the current language is not saved in the AS entity.
This means that, when there is a change in the product inventory, the system is unable to know in which language the customer needs to receive the email and the default one is always chosen.

Describe the solution you'd like
To solve the issue, we could save the language / locale in the AS entity as soon as the customer subscribes for the availability notification and use that infrormation in order to trigger the email in the correct language.
This way, any VETX account will be able to use this data to send the notification in the correct language in any multu-language store.
Also, it would be a good idea to also save the sales policy the customer belongs to, in order to only send the notification to the customer when the inventory changes in a warehouse which has a langing dock tied to that sales policy.