Adding a new locale to Beta and Release builds


The majority of the technical work has already been completed when setting up Nightly builds.

There are a few important prerequisites before adding a new locale to Beta and Release.

For the localization community:

  • Localization should have reached a high level of completion, especially for user facing parts of the UI:
    • All Tags with high priority (4 and 5 stars) should be at 100% (or very close).
    • Lower priority Tags should be at least above 30%.
  • Localization team has demonstrated a consistent effort, being able to keep up for at least a couple of cycles with the incoming flow of new strings.
    • There must be more than one active translator on the project, to ensure that the content has been peer reviewed.
  • There is a relevant number of users on the Nightly channel testing the localization. This number varies based on the language, for minority languages 10-20 users is an excellent result. Also, a trend showing growth is important as well.

For the localization PM:

To track this work, you need to file a bug in Firefox::Build Config (like this example), blocking the original tracking bug for the locale (fx-l10n-LOCALE).

Verify language name

First of all, make sure that MOZ_LANG_TITLE in toolkit/ has the correct value, since it’s used to set up the language pack on AMO.

The language name associated to the locale code is displayed in a few places in Firefox interface (language settings for web content, contextual menu for dictionaries). The language name needs to be defined in:

  • languageNames.ftl: ID with structure language-name-LOCALECODE = (name of the language in English). Note that the locale code can only be a 2/3 letter code, locales like ca-valencia are not valid.
  • mozIntl.jsm:
    • Add the locale code in the availableLocaleDisplayNames constant, language set.
    • Add the localized language name in the nativeLocaleNames map. The localized language name should also be stored in this repository.
  • add a value in the form LOCALECODE.accept = true. This is needed to list the language in the language settings dialog for web content.

Add locale to build configuration

First of all make sure that your environment is correctly set up, update your local mozilla-unified clone and make sure it’s on the central bookmark:

$ cd ~/mozilla/mercurial/mozilla-unified
$ hg pull -u
$ hg up central

The file to modify is in browser/locales/shipped-locales, open it with your text editor of choice.

$ atom browser/locales/shipped-locales

And add the new locale to the list. With Atom and the Sort Lines package installed, you can press F5 to make sure that the list is in alphabetical order.

After you’ve finished editing the file, check the status of the repository, and the diff. Let’s consider for example the task of adding Urdu (ur).

$ hg status
M browser/locales/shipped-locales

$ hg diff
--- a/browser/locales/shipped-locales
+++ b/browser/locales/shipped-locales
@@ -83,14 +84,13 @@ son

M in hg status indicates that the file has been modified, + in hg diff that the line has been added. Follow the instructions available in this document to create a patch, submit it for review, and land it.

You also need to set the relnote-firefox flag to ? in the bug, the suggested comment is Suggested for release notes: "Locale added: LANGUAGE_NAME (LOCALE_CODE)".

Update language pack settings on AMO

The language pack for the new locale will be uploaded automatically by release automation on (starting with the Beta version). A few follow-up manual steps are needed:

  • The Mozilla account needs to be added as author for the language pack.
  • The target_locale field needs to be set for the language pack (via Django admin UI).
  • The locale needs to be defined in this JavaScript file.

For the first two steps, an email needs to be sent to AMO administrators (amo-admins(at)

These steps will make the language pack available in both the Language Tools page and the API used by Firefox to add new languages from preferences.