The Message Definitions file for United States English is named TRD0LENU; it is provided on a release tape.
The Assembler file for TRD0LENU is on the z/OS release tape as member CL2ASSEM.
No action is required to use this file for messages in United States English. The file is provided to be used as the basis for creation of message definitions in other languages. Refer to Chapter 14: “Message Definitions,” for details.