Why Internationalization is Easy and Localization is Hard

JavaScript has a really powerful built-in library for internationalization, but very little support for localization. For the past few years, I've been closely involved with work trying to address this imbalance, defining the Unicode MessageFormat specification, championing the Intl.MessageFormat JS proposal in TC39, and working on other related proposals in TC39 and W3C/WHATWG. I'll share with you the current state of the art, what's already possible, and some of the reasons why "solving" localization is so difficult.