You haven't commented too much on the specifics of how your application interacts with the user or generates HTML pages - Depending upon how much of this has been built within your application, a lot of work could be shifted into template files. This allows for the generation of locale-specific output with a simple change of the output template employed by your script.

Furthermore, this allows for a clear distinction between code and presentation, such that there is no need to rewrite the code base for each language which your application supports.

If you are interested in pursuing this development path, I would recommend that you explore the feature-set of the Template Toolkit before re-inventing any wheels.