PHPMaster.com: Localizing PHP Applications "The Right Way", Part 1
Localizing software applications in general used to be a cumbersome and error-prone task resulting in a lot of messy code. Some developers even use different versions of code for the same application but for different locales, which makes managing the codebase practically impossible. Enter gettext, the wonderful open-source tool that will make your life easier by allowing you to concentrate on your code. Localization becomes a matter of writing separate translation files for the target language, which can easily be done by a translator using Poedit.
They help you get your environment set up - PHP and a href="http://poedit.net/"Poedit, a gettext catalog editor - for both linux- and Windows-based OSes. They walk you through the creation of a simple project and a few basic "hello world" tokens. Using the files is as easy as setting the correct locale and default domain for your application. Then output is just a basic echo away.