Added missing translation for back_to_shipping_categories_list

Fixes #4993
Do not blindly accept just any month for CreditCard expiry

Fixes #4971
Silence two warnings

Fixes #4985

Silences this:

    [WARNING] You are not setting Devise.secret_key within your application!
    You must set this in config/initializers/devise.rb. Here's an example:

And this:

    [deprecated] I18n.enforce_available_locales will default to true in the future. If you really want to skip validation of your locale you can set I18n.enforce_available_locales = false to avoid this message.

in the sandbox app.
Added localization for multiple SKU info

Fixes #4994
Validate price maximum.

Price is constrained to be precision: 8, scale: 2 at the database level,
but that validation isn't reflected in the model.

This will lead to errors when prices are 1,000,000 or above, which is a
lot in USD, but 1 million Vietnamese Dongs is less than $50 USD.

Fixes #4944