While Facebook continues rolling out new features around birthday calendaring and gifting, popular app Birthday Calendar is continuing to grow by taking a road less traveled by most Platform applications: translation into many languages.

With about 7.5 million monthly active users today, Birthday Calendar is the 2nd most popular app for Facebook users in French, Spanish, and Italian (Pet Society by Playfish is #1 in all three). BigDates Solutions, the developer of Birthday Calendar, is using Facebook’s crowd-sourced translation service to let users translate the app into their local language.

Here’s how it looks:

Inside Facebook’s Karl Bunyan recently wrote a tutorial for developers interested in translating their apps. (Facebook’s translation tool is very powerful, but your apps must be built in FBML.) However, as Birthday Calendar is showing, it very well could be well worth your effort.

With over 67 million active Facebook users in Europe, many more Facebook apps would likely gain significant additional traction were they to translate their applications too.

AppData for Birthday Calendar – Last 90 Days