chrome.i18n | API | Chrome for DevelopersManifest If an extension has a /_locales directory, the manifest must define "default_locale". Concepts and usage You need to put all of its user-visible strings into a file named messages.json. Each time you add a new locale, you add a messages file under a directory named /_locales/_localeCode_, where localeCode is a code such as en for English. Here's the file hierarchy for an internationalized
