I suggest you back up and consider the more general problem - separating the interface to your program from the core logic. If you do a good job of that you may not have to resort to a message catalog right away (although that might still be a good idea, depending on how you rate the chances of an i18n project in your future).

In the web world the most common way to separate interface from logic is via a model-view-controller architecture (MVC). You didn't give us enough information to guess whether that would be directly applicable to your app, but anything you can do to make your code interface-agnostic will help you when it comes time to make cosmetic changes, i18n changes included.

-sam