[Editor's Note: The data cited in this article is excerpted from Inside Facebook Gold, our membership service tracking Facebook's business and growth around the world. Visit Inside Facebook Gold to learn more about our complete data and analysis offering.]

English is still by far the most-used language on Facebook, with some 231 million users. However, Facebook just crossed the 500 million user milestone — which means that over half of all users are accessing the site in another language. With an increasingly international audience, where should marketers and application developers focus their attention?

Earlier this week, we detailed the growth of Facebook’s top 10 languages. In a sense, our findings provided an easy answer to the above question. Spanish, with 68 million users, is Facebook’s second-largest language; that’s roughly the population of France. In turn, French is third-largest, with 26 million users. These user groups are easily large enough to warrant attention.

However, large groups of foreign-language users can also be a double-edged sword. On the positive side, people in a particular language group are now together on one platform in a way that they never before have been.

The negative, at least for some purposes, is that the geographic distribution of these users is extremely wide. Very few Spanish-language users are in the United States; meanwhile, even the top five countries for the language only represent about 50 million of the total group:

It’s easy to imagine scenarios in which it would be desirable to reach all of the users of a particular language; educational products, for instance, know no borders. However, a company that can only effectively distribute its product in a certain region — continental Europe, for example — may find it more worthwhile to focus on a concentrated language group like Turkish, in which all but handful of the 23 million users are in Turkey itself.

For application developers and others who want to maintain an online-only contact with their audience, Facebook’s language stats still present some challenges. For instance, Indonesian is now the fifth-largest language on Facebook with 21 million users. Appealingly, the country’s population is known for a willingness to spend online, albeit in smaller amounts than people in richer countries.

However, in an interview on Inside Social Games, Wooga CEO Jens Begemann told us his gaming company has stopped targeting Indonesians, among other Asian groups, in part because the Indonesians who are online are likely to have basic fluency in English anyway, obviating the need for his company to do extra translation work.

Wooga’s plan is to add other language groups in the future, including Portuguese, which grew 11.8 percent over the past month due to new Brazilian users, but for the moment still has only 7.2 million users — not quite enough for the company to invest in the market.

In the end, the decision of which market to invest in should mainly balance the number of potential users, their likelihood to monetize well, and the unique situation of the company planning to localize its product or application. But there are many more potential considerations, including the average age and sex of users in each language group; those metrics are available as part of an Inside Facebook Gold subscription.