One other idea that I think would be useful for speed reasons would be if you were to provide support for Zend Server acceleration and caching. We currently use the community edition of Zend server, and have found that the caching features are very good for our own code. The Shared Memory storage that the server offers would be a good fit for your localization system since all of the language files and keys could be loaded into shared memory once and wouldn't have to be initialized with every page see more load. The other nice thing is that Zend Server's shared memory API is very simple to implement, and only requires a single function call each to save/recall/clear a particular key in Shared Memory.