On the Lingohub site there's a new post showing how internationalization (i18n) is handled in 5 major PHP frameworks - CodeIgniter, CakePHP, Zend Framework Symfony and Yii.

As discussed in the previous articles on PHP internationalization, PHP provides native support for string translation using gettext and PHP arrays. These can be used in any PHP project. Additionally, some popular PHP frameworks offer their own way of string translation. In this article, I want to provide a brief summary of the internationalization process with five of the most popular PHP frameworks currently out there. In this How-To you will read about using CodeIgniter, CakePHP, Zend, Yii and Symphony.

There's only a bit of sample code here, so it's not a complete tutorial for all of them. Mostly its links to more information about how each framework does things - modules used, formats and configurations.