Internationalize the interface

Use the chrome.i18nAPI to internationalize your extension. Start by creating directories to hold language-specific message files within a folder called _locales/. For example:

_locales/en/messages.json
_locales/es/messages.json

Each messages.json file will contain localized strings identified by a key. For example, the following code localizes the tooltip for _locales/en/messages.json. The key for this string is __MSG_tooltip__.

{
  "__MSG_tooltip__": {
   "message": "Hello!",
   "description": "Tooltip"
 }
}

You will use this key inside the manifest.json in place of the "default_title".

{
  "name": "Tab Flipper",
 ...
  "action": {
    "default_title": "__MSG_tooltip__"
  },
  "default_locale": "en"
 ...
}

For more information, see Localization message formats.