The Messages property is included only for backward compatibility with sites created in Commerce Server 2.0, and will be discontinued in future releases. Use the Language property of the PipeContext object to pass the desired message set to the order processing pipeline (OPP) components.
The Messages property identifies the alias of the message sets to use to return basket and purchase errors in the OrderForm. This value must identify one of the message sets added to the MessageManager through a call to that object’s AddLanguage method.