chrome.i18n

Description: Use the chrome.i18n infrastructure to implement internationalization across your whole app or extension.
Availability: Since Chrome 5.
Content Scripts: Fully supported. Learn more

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 extension that supports English (en), Spanish (es), and Korean (ko):

In the extension directory: manifest.json, *.html, *.js, _locales directory. In the _locales directory: en, es, and ko directories, each with a messages.json file.

How to support multiple languages

Say you have an extension with the files shown in the following figure:

A manifest.json file and a file with JavaScript. The .json file has "name": "Hello World". The JavaScript file has title = "Hello World";

To internationalize this extension, you name each user-visible string and put it into a messages file. The extension's manifest, CSS files, and JavaScript code use each string's name to get its localized version.

Here's what the extension looks like when it's internationalized (note that it still has only English strings):

In the manifest.json file, "Hello World" has been changed to "__MSG_extName__", and a new "default_locale" item has the value "en". In the JavaScript file, "Hello World" has been changed to chrome.i18n.getMessage("extName"). A new file named _locales/en/messages.json defines "extName".

Important: If an extension has a _locales directory, the manifest must define "default_locale".

Some notes about internationalizing:

  • You can use any of the supported locales. If you use an unsupported locale, Google Chrome ignores it.

  • In manifest.json and CSS files, refer to a string named messagename like this:
    __MSG_messagename__
  • In your extension or app's JavaScript code, refer to a string named messagename like this:
    chrome.i18n.getMessage("messagename")
  • In each call to getMessage(), you can supply up to 9 strings to be included in the message. See Examples: getMessage for details.

  • Some messages, such as @@bidi_dir and @@ui_locale, are provided by the internationalization system. See the Predefined messages section for a full list of predefined message names.

  • In messages.json, each user-visible string has a name, a "message" item, and an optional "description" item. The name is a key such as "extName" or "search_string" that identifies the string. The "message" specifies the value of the string in this locale. The optional "description" provides help to translators, who might not be able to see how the string is used in your extension. For example:
          {
            "search_string": {
              "message": "hello%20world",
              "description": "The string we search for. Put %20 between words that go together."
            },
            ...
          }

    For more information, see Formats: Locale-Specific Messages.

Once an extension or app is internationalized, translating it is simple. You copy messages.json, translate it, and put the copy into a new directory under _locales. For example, to support Spanish, just put a translated copy of messages.json under _locales/es. The following figure shows the previous extension with a new Spanish translation.

This looks the same as the previous figure, but with a new file at _locales/es/messages.json that contains a Spanish translation of the messages.

Predefined messages

The internationalization system provides a few predefined messages to help you localize. These include @@ui_locale, so you can detect the current UI locale, and a few @@bidi_... messages that let you detect the text direction. The latter messages have similar names to constants in the gadgets BIDI (bi-directional) API.

The special message @@extension_id can be used in the CSS and JavaScript files, whether or not the extension or app is localized. This message doesn't work in manifest files.

The following table describes each predefined message.

Message name Description
@@extension_id The extension or app ID; you might use this string to construct URLs for resources inside the extension. Even unlocalized extensions can use this message.
Note: You can't use this message in a manifest file.
@@ui_locale The current locale; you might use this string to construct locale-specific URLs.
@@bidi_dir The text direction for the current locale, either "ltr" for left-to-right languages such as English or "rtl" for right-to-left languages such as Japanese.
@@bidi_reversed_dir If the @@bidi_dir is "ltr", then this is "rtl"; otherwise, it's "ltr".
@@bidi_start_edge If the @@bidi_dir is "ltr", then this is "left"; otherwise, it's "right".
@@bidi_end_edge If the @@bidi_dir is "ltr", then this is "right"; otherwise, it's "left".

Here's an example of using @@extension_id in a CSS file to construct a URL:

      body {
        background-image:url('chrome-extension://__MSG_@@extension_id__/background.png');
      }
      

If the extension ID is abcdefghijklmnopqrstuvwxyzabcdef, then the bold line in the previous code snippet becomes:

      background-image:url('chrome-extension://abcdefghijklmnopqrstuvwxyzabcdef/background.png');
      

Here's an example of using @@bidi_* messages in a CSS file:

      body {
        direction: __MSG_@@bidi_dir__;
      }
      
      div#header {
        margin-bottom: 1.05em;
        overflow: hidden;
        padding-bottom: 1.5em;
        padding-__MSG_@@bidi_start_edge__: 0;
        padding-__MSG_@@bidi_end_edge__: 1.5em;
        position: relative;
      }
      

For left-to-right languages such as English, the bold lines become:

      dir: ltr;
      padding-left: 0;
      padding-right: 1.5em;
      

Locales

You can choose from many locales, including some (such as en) that let a single translation support multiple variations of a language (such as en_GB and en_US).

Supported locales

You can use any of the locales that the Chrome Web Store supports.

Searching for messages

You don't have to define every string for every supported locale. As long as the default locale's messages.json file has a value for every string, your extension or app will run no matter how sparse a translation is. Here's how the extension system searches for a message:

  1. Search the messages file (if any) for the user's preferred locale. For example, when Google Chrome's locale is set to British English (en_GB), the system first looks for the message in _locales/en_GB/messages.json. If that file exists and the message is there, the system looks no further.
  2. If the user's preferred locale has a region (that is, the locale has an underscore: _), search the locale without that region. For example, if the en_GB messages file doesn't exist or doesn't contain the message, the system looks in the en messages file. If that file exists and the message is there, the system looks no further.
  3. Search the messages file for the default locale. For example, if the extension's "default_locale" is set to "es", and neither _locales/en_GB/messages.json nor _locales/en/messages.json contains the message, the extension uses the message from _locales/es/messages.json.

In the following figure, the message named "colores" is in all three locales that the extension supports, but "extName" is in only two of the locales. Wherever a user running Google Chrome in US English sees the label "Colors", a user of British English sees "Colours". Both US English and British English users see the extension name "Hello World". Because the default language is Spanish, users running Google Chrome in any non-English language see the label "Colores" and the extension name "Hola mundo".

Four files: manifest.json and three messages.json files (for es, en, and en_GB).  The es and en files show entries for messages named "extName" and "colores"; the en_GB file has just one entry (for "colores").

How to set your browser's locale

To test translations, you might want to set your browser's locale. This section tells you how to set the locale in Windows, Mac OS X, and Linux.

Windows

You can change the locale using either a locale-specific shortcut or the Google Chrome UI. The shortcut approach is quicker, once you've set it up, and it lets you use several languages at once.

Using a locale-specific shortcut

To create and use a shortcut that launches Google Chrome with a particular locale:

  1. Make a copy of the Google Chrome shortcut that's already on your desktop.
  2. Rename the new shortcut to match the new locale.
  3. Change the shortcut's properties so that the Target field specifies the --lang and --user-data-dir flags. The target should look something like this:
    path_to_chrome.exe --lang=locale --user-data-dir=c:\locale_profile_dir
  4. Launch Google Chrome by double-clicking the shortcut.

For example, to create a shortcut that launches Google Chrome in Spanish (es), you might create a shortcut named chrome-es that has the following target:

path_to_chrome.exe --lang=es --user-data-dir=c:\chrome-profile-es

You can create as many shortcuts as you like, making it easy to test in multiple languages. For example:

path_to_chrome.exe --lang=en --user-data-dir=c:\chrome-profile-en
      path_to_chrome.exe --lang=en_GB --user-data-dir=c:\chrome-profile-en_GB
      path_to_chrome.exe --lang=ko --user-data-dir=c:\chrome-profile-ko

Note: Specifying --user-data-dir is optional but handy. Having one data directory per locale lets you run the browser in several languages at the same time. A disadvantage is that because the locales' data isn't shared, you have to install your extension multiple times — once per locale, which can be challenging when you don't speak the language. For more information, see Creating and Using Profiles.

Using the UI

Here's how to change the locale using the UI on Google Chrome for Windows:

  1. Wrench icon > Options
  2. Choose the Under the Hood tab
  3. Scroll down to Web Content
  4. Click Change font and language settings
  5. Choose the Languages tab
  6. Use the drop down to set the Google Chrome language
  7. Restart Chrome

Mac OS X

To change the locale on Mac, you use the system preferences.

  1. From the Apple menu, choose System Preferences
  2. Under the Personal section, choose International
  3. Choose your language and location
  4. Restart Chrome

Linux

To change the locale on Linux, first quit Google Chrome. Then, all in one line, set the LANGUAGE environment variable and launch Google Chrome. For example:

      LANGUAGE=es ./chrome
      

Examples

You can find simple examples of internationalization in the examples/api/i18n directory. For a complete example, see examples/extensions/news. For other examples and for help in viewing the source code, see Samples.

Examples: getMessage

The following code gets a localized message from the browser and displays it as a string. It replaces two placeholders within the message with the strings "string1" and "string2".

      function getMessage() {
        var message = chrome.i18n.getMessage("click_here", ["string1", "string2"]);
        document.getElementById("languageSpan").innerHTML = message;
      }
      

Here's how you'd supply and use a single string:

      // In JavaScript code
      status.innerText = chrome.i18n.getMessage("error", errorDetails);
      
      "error": {
        "message": "Error: $details$",
        "description": "Generic error template. Expects error parameter to be passed in.",
        "placeholders": {
          "details": {
            "content": "$1",
            "example": "Failed to fetch RSS feed."
          }
        }
      }
      

For more information about placeholders, see the Locale-Specific Messages page. For details on calling getMessage(), see the API reference.

Example: getAcceptLanguages

The following code gets accept-languages from the browser and displays them as a string by separating each accept-language with ','.

      function getAcceptLanguages() {
        chrome.i18n.getAcceptLanguages(function(languageList) {
          var languages = languageList.join(",");
          document.getElementById("languageSpan").innerHTML = languages;
        })
      }
      

For details on calling getAcceptLanguages(), see the API reference.

Summary

Methods
getAcceptLanguages chrome.i18n.getAcceptLanguages(function callback)
getMessage string chrome.i18n.getMessage(string messageName, any substitutions)
getUILanguage string chrome.i18n.getUILanguage()

Methods

getAcceptLanguages

chrome.i18n.getAcceptLanguages(function callback)

Gets the accept-languages of the browser. This is different from the locale used by the browser; to get the locale, use i18n.getUILanguage.

Parameters
function callback

The callback parameter should be a function that looks like this:

function(array of string languages) {...};
array of string languages

Array of the accept languages of the browser, such as en-US,en,zh-CN

getMessage

string chrome.i18n.getMessage(string messageName, any substitutions)

Gets the localized string for the specified message. If the message is missing, this method returns an empty string (''). If the format of the getMessage() call is wrong — for example, messageName is not a string or the substitutions array has more than 9 elements — this method returns undefined.

Parameters
string messageName

The name of the message, as specified in the messages.json file.

any (optional) substitutions

Up to 9 substitution strings, if the message requires any.

getUILanguage

string chrome.i18n.getUILanguage()

Since Chrome 35.

Gets the browser UI language of the browser. This is different from i18n.getAcceptLanguages which returns the preferred user languages.