Should I translate my app?

Right now, because of the crisis, non-American iPhone owners tend to have more money to spend on apps than Americans. If you wish to tap into that market, your app pretty much has to be available in your customers' language - and not just in a crappy automatic translation either. Customers are several times as likely to buy something online if the description is in their language, assuming of course that the translated description sounds just as alluring and just as professional as the original.

Another reason to translate your app is that non-Americans have somewhat different tastes. Just compare the top 10 paid apps in a foreign App Store with the ones in the American App Store. Some game developers for example make the majority of their sales in South America, and not nearly as many in the states. When you translate an app that isn't faring so well in the USA, there is always a chance that it will hit a nerve in a foreign market.

Finally, many developers have deliberately limited the sale of their app to North America, so that it doesn't even show up in other countries' App Stores. There are a few valid reasons, e. g. if there are copyright or legal issues publishing the app outside a certain country, but most developers are probably just not thinking. The traditional reasons for limiting your market (high postage fees, insecure payments, not wanting to negotiate with shop owners abroad, etc.) do not apply here, because Apple is already taking care of all of that. To increase your income with foreign customers, all you have to do is to allow Apple to sell your app around the world and wait for the money to come in. If not everybody is doing it, that's another point in favor of you doing it: you have less competition.

Is my app translateable?

Almost all apps are. The only apps that are hard or impossible to translate are word games. Even for a decidedly local app, such as a San Francisco restaurant finder or a Berlin public transport map, offering foreign-language versions is typically a good idea because of all the tourists taking advantage of these apps. As a tourist in a foreign city, I am in fact much more likely to use this kind of app than a resident would be.