Here are some useful resources for Android development.

Internationalization

• Internationalizing an Android app

Design

• Android Asset Studio
• Android Cheatsheet for Graphic Designers
• Android Developer Icons
• Android Icons
• Material icons guide
• Android Transition animations explanation with examples

Fragments

• Les Fragments

Asynchronism

• Run multi AsyncTask at the same time

Security

• Using Cryptography to Store Credentials Safely
• Secure your app: Fight the leaks! - Samsung

Libraries

• Android Arsenal
• Libraries for developers
• Top 5 Android libraries every Android developer should know about

Finalizing the app / promoting it

• Free iPhone Mockup Generator & App Demo Videos by Placeit
• Device Art Generator
• Android App Publishing Checklist

Testing

• No more excuses, Android testing is possible
• 3 unit tests to avoid bad surprises on Android

Continuous Integration

• Use GoCD for Android and get rid of Jenkins
• DevOps on Android: From one Git push to production and the talk given by the author
• Continuous Integration on Android

Further reading

• Developing for Android: Introduction
• Deep Dive Into State Restoration (en) - Cyril Mottier, Capitaine Train - Droidcon Paris 2014
• A Story of Software Development Methodologies