Android apps are global, they get downloaded all around the world. And this means not only supporting multiple languages via xml files. Its about plurals, date formats, currencies up to things like right-to-left
This topic tries to give an introduction into this large topic for new developers.
I did a specific talk about Right-to-Left 2015 and realized lots of developers still need to know the basics. Groupon apps supports many languages and countries, so there are real examples.