Payer.LanguageCodeparameter with the PaymentPage Initialize request. A list of all supported languages and their code, can be found with the request specification.
Billing|DeliveryAddressForm.AddressSource, within the Payment Page Initialize request. As the name suggests, it controls the source of the payers address and it has three values:
SAFERPAY-option and display an address form on the payment page itself.
PaymentMethodsarray, through the Payment Page Initialize request.
Payer.Billing|DeliveryAddress, but instead inside
PaymentMeans.PayPalcontainer, as this can differ from the e-mail, that is saved within the address!