I'm not from Pair but I can tell you after using apktool on their apk file. It looks like a well written normal Android app supporting a variety of screen size

I'm not from Pair but I can tell you after using apktool on their apk file. It looks like a well written normal Android app supporting a variety of screen sizes on Android 2.2 and above. Text is only available in English. They use regular Android screen layouts and widgets inside (lists, images, text etc). The Android compatibility library is used (primarily fragments) so it should layout well no matter what. They have composed their app using numerous different Activities as is best practise for Android, although they force several into portrait mode. Mixpanel is used for analytics. There are several "realtime" sockets related thirdparty libraries. All the code was Java (ie no C/C++/ObjC was involved). I obviously can't see their source code, but based on what I do see they have a textbook example of how to write an Android app following best practises.