UTF-16 is the internal format of the ICU library (International Components for Unicode, the support library from the Unicode standards people) which is a common way to add "full fat" Unicode support to a programming language. This has knock-on effects everywhere. If you're using ICU, you either use UTF-16, too, or you constantly convert back and forth every time you interact with ICU. You're often best off using UTF-16 in memory and only converting to UTF-8 when you write files or transmit over the network.