In the latest installment of their "Localizing PHP Applications 'The Right Way'" tutorial series (part four), they show off a feature of gettext that makes it simpler to deal with singular versus plural versions of your translations.
In Part 3 you learned some of the more important aspects of real-world localizing your application, such as using a default fallback locale and separating messages into multiple domain files depending on their usage. In this part I’ll show you what is arguably the most powerful feature of gettext – handling plural forms. The plural forms feature of gettext you enable you to localize your application perfectly and professionally.
The simple example they give is the difference between things like "1 file" versus "2 files". English is simpler than some other languages but gettext has special handling you can add to your translation files to help. A rule placed at the top of your file defines where to start the singular vs plural switch.