When enabled, the language that the e-commerce site was localized in when a purchase was made will be stored in the sales order. That language code will be used when selecting an email template when sending transactional emails for the order. Previously, the language of the default customer object was used, which could result in emails that were localized in a language the customer didn't understand. NOTE: to ensure that transactional emails continue to function correctly after this feature is enabled, make sure you have a template for every language your e-commerce site is localized in, that you have set the default language set for every template, and that a template exists for the default language.