1. You can customize the text and language of error messages by using the Websydian pattern MessageStore. Please refer to the documentation for more details (http://www.websydian.com/websydiandoc/WsyPres/MsgStore/Default.htm).
   This pattern enables support for multi-language applications as well as logging of the error messages that are reported by the application.
    
2. A simpler solution is to modify each pattern that generates an error message. E.g. the session error messages can be modified by changing the message objects scoped under the EventDispatcher function.
   For other error messages you should create a function that inherits from WSYBASE/WebShell. In the pre point 'Start send message' you can change the text of the error message by changing the value of the field Environment<*Message text>.

When you have done this then let your EventHandler, PageGenerator, and EventDispatcher functions inherit from the new WebShell function.
This solution only supports one language and the reported errors are not logged.