Best mobile apps developer and UI designer for next killer apps

I am looking for the best mobile apps developer and designer who can solve the the problems of making an apps that can be marketed in many different countries in the world (US market first, China market) in both iPhone and Android platform. Currently we have mobile apps developer from China which has mainly Chinese content. We will roll out this mobile apps in the US market. Note that China apps will have different features from US apps. We need to hire experienced apps developer who is able to make sure that US customers can only see US based or content in English (without seeing Chinese content), even though the apps itself has Chinese content mainly. The current China developer said UI language can automatically be changed based on iPhone setting language. But surely this is not what US customers would prefer to see, because the content is still Chinese (menu in English only). Please recommend if we should make one apps (use youtube as an example), which can show content relates to that country where the users come from? US customers see English content, Chinese customers see Chinese content in one single apps or two separate apps. Proposed apps site structure and hosting solution must provide excellent streaming experience. Your willingness to study the market prior to start working on the project so that it helps us to deliver the best user experience and user interface will be great asset and bonus to the success of this project. Kindly share your prior experience if you have done so.