using gettext format could bring the following pros:
- Extract the language definitions from source code with lots of tools or the sample code from other PHP applications
- Translators could translate modules without touch the source code with editors like poedit( http://www.poedit.net/ ) and more
- Translators could collaborate in many platforms, like Launchpad( https://dev.launchpad.net/Getting ), Pootle( http://translate.sourceforge.net/wiki/pootle/ ) or even Drupal ( http://localize.drupal.org/ ). The friends in Taiwan also made a similar tool for localization in Chinese.
- Modules could share the language definitions and translators don't have to translate the same sentences again and again.