I have several iOS/iPhone apps that have been continually selling in small amounts in over 2 dozen different countries, even though the app UIs and all the store descriptions are only in English.  In a few countries where English is not the official or native language, a few apps are selling far better than is proportionate for those country's population size compared with the U.S.So why Internationalize apps?What kind of increase, if any, in sales might a typical app see if it is Internationalized into given local languages?  Which major languages might be likely to see the greatest improvement in app sales or downloads due to a localized app description?
Value of Internationalization in the iPhone App store?
iphone;internationalization
It's going to depend on your market.If your market is a largely technical or is quite niche then translating probably isn't an issue as your users are probably OK with it being in English and in some cases may actually prefer it being in English.If your market is the general population then translation is probably a good idea as it will increase the reach of your application. In certain countries that protect their native languages (e.g. France) translation would be pretty much essential.So you need to analyse your current market and where you want to go with your apps to see if internationalisation is actually worth it. Then tackle the languages in market order, but languages like French, Spanish and Portuguese that are either 1st or 2nd languages in a number of countries would seem to be the most obvious choices.