You don't have to learn a new language: PHP-GTK. 😉
I'd say that you should go ahead and learn the new language if you think that you're going to need it in the future. If you're referring to C or C++, then I think that you should. That way, you'll be able to more than just web programming.
However, if you intend on sticking to web programming in the future and not expanding your horizons, then I would go the web browser way. This would also be the thing to do if you have limited time for the project.
But if you have time, I'd learn the new language. In the competitive job market that there is today, you can never know to many languages. (Learning Mandarin Chinese might help too. 😉)