I make Mac apps, and they are English only, even though my native language is German. Translating the app to German would be straightforward, since I could do it myself. However, it would make future development much more complex; I'm already struggling to keep up with one language. Especially for German I don't think that the effort would pay off; most German speakers understand English reasonably well (epsecially in my target demographic).
However, some countries are different. For example, I frequently get poor reviews from Spain; it's obvious that the people complaining didn't understand the description and purchased the wrong app. It fits my personal experience/prejudice that people in Spain are less likely to speak English. However, a Spanish translation would be more difficult because I'd need to hire someone, and I'm not sure if additional sales in Spain would make up for the up-front translation costs.
But, it's something to keep in mind: Consider how much of your target demographic speaks English even though it's not their native language. There are large variations among different demographics.