• $NewMessage is a global variable which, if set, is applied to the symbol name and tag of messages that are requested but have not yet been defined.
• $NewMessage is applied to the symbol name, tag and language of a message if an explicit language is specified.
• Mathematica looks for the value of name::tag or name::tag::lang after $NewMessage has been applied.
• You can set up $NewMessage to read the text of messages from files when they are first needed.
• A typical value for $NewMessage might be Function[ToExpression[FindList[files, ToString[MessageName[#1, #2]]]]].
• New in Version 2.