From the author of My Year as an Amateur Android Game Developer, which came across earlier today [1]. I was startled to see that over 40% of my users were Spanish-speaking (Spanish-speaking users make up only about 3% of all Android Market users). I added the Spanish translation more or less on a whim; I suppose it let me compete in a more narrow market.
[1] http://news.ycombinator.com/item?id=2368077