Localization community, tools & process, part 2 of 3 – A Node.js holiday season, part 10

This is episode 10, out of a total 12, in the A Node.JS Holiday Season series from Mozilla’s Identity team. Let’s talk some more localization!

El equipo de Localización

In our previous post “How to Localize Your Node.js service”, we learned how to add i18n-abide to our code.

We wrapped strings in both templates and JavaScript files.
As developers, our work ends there. But the work of getting our prose localized has just begun.

The toolchain

Persona’s Node.js based L10N toolchain is compatible with the larger Mozilla community, but retains the friendliness and flexibility that Node is known for.

The Mozilla project is nearly 15 years old, with one of the biggest (and coolest) L10n communities in Open Source.
As a result, it has many existing tools, sometimes old crotchety tools.


GNU Gettext is a toolchain that allows you to localize text from webapps or native apps. When you write your Node.js code and templates, you put in English strings like normal, but each string is wrapped in the function call ‘gettext’.

gettext does a few different things for you:

  • During a build step, gettext extracts all the strings into a string catalog
  • At runtime, gettext replaces the English string with its localized equivalent.

String extraction during the build step is how we’ll create a catalog of strings from your code and template files.

All these strings end up in text files that end with the .po file suffix. I’ll refer to these as PO files.

PO Files

.PO files are plain text files with a specific format that the Gettext tools can read, write, and merge.

An example snippet of a PO file named zhTW/LCMESSAGES/messages.po:

#: resources/views/about.ejs:46
msgid "Persona preserves your privacy"
msgstr "Persona 保護您的隱私"

We’ll examine this in more detail below, but we can see that msgid is the English String and msgstr has the Chinese translation. Comments are anything that start with a #.
The comment above shows the location in the codebase the string is used.

Gettext provides many other tools: it can manage Strings, PO files, etc. We’ll cover these in a bit.

Why a new toolchain?

Before we get into the Node modules that make working with Gettext easy, we must ask ourselves… why this toolchain?

A year ago I did a deep survey of all the Node L10n and I18n modules.
Most “reinvent the wheel”, creating their own JSON based formats for storing Strings.

The Mozilla community already uses many tools such as POEdit, Verbatim, Translate Toolkit, and Pootle. Instead of forcing new tools on the community, we decided to make our tools work within their standards.

Which is how we’ll tell our localizers what all of our strings are and how they will give us the finished translations. PO files are the data exchange medium of the L10n community.

Coming from PHP and Python at Mozilla, I’ve found that Gettext works very well. As a web application gets large and has more prose, there are many nuances of localizing text that require the well tested tools and APIs of gettext.

Providing PO Files to localizers

So our code is marked up with gettext calls. Now what?
Get thee a String wrangler. This person or persons can be you, a localization expert, or a build system guru.

What does a String wrangler do?

  • First time extraction of Strings from the software
  • Extract new, changed, or note deleted strings in later releases
  • Prepare the PO files for each localizer team
  • Resolve conflicts and mark strings which have changed or been deleted

This may sound complicated, but there is some good news!
These steps can be automated. Most of these steps can be automated. When problems crop up, the string wrangler is responsible for them.

msginit, xgettext, msgfmt and other GNU Gettext tools tools are a powerful way to manage catalogs of Strings. Only the String wrangler needs these tools, most developers (as well as Node.js) can remain blissfully ignorant of them.

Setup locale filesystem

$ mkdir -p locale/templates/LC_MESSAGES

This directory is where we’ll store the PO template or POT files. The POT files are used by the Gettext toolchain.

Extract the Strings

In the last post, we installed i18n-abide with

npm install i18n-abide

Among other command line tools, it provides extract-pot.
To extract strings into a locale directory, we would use this command.

mkdir -p locale/templates/LC_MESSAGES
$ ./node_modules/.bin/extract-pot --locale locale .

extract-pot creates a .POT file, which is a PO file Template.

This script will recursively look through your source code and extract Strings.

So how does extract-pot create these POT files? You can use traditional GNU Gettext utilities, but we’ve also written a Node module jsxgettext, which is a nice cross platform way to go.
extract-pot uses jsxgettext behind the scenes.

jsxgettext parses your source files looking for uses of Gettext functions, and then it extracts just the String part. It then formats a PO file, which is compatible with any other Gettext tool.

Here is an excerpt from a POT File.

#: resources/views/about.ejs:46
msgid "Persona preserves your privacy"
msgstr ""

#: resources/views/about.ejs:47
msgid ""
"Persona does not track your activity around the Web. It creates a wall "
"between signing you in and what you do once you're there. The history of "
"what sites you visit is stored only on your own computer."
msgstr ""

#: resources/views/about.ejs:51
msgid "Persona for developers"
msgstr ""

Later, we’ll create PO files from this template.

After your localizers edit their PO file, it will look more like this:

#: resources/views/about.ejs:46
msgid "Persona preserves your privacy"
msgstr "Persona 保護您的隱私"

#: resources/views/about.ejs:47
msgid ""
"Persona does not track your activity around the Web. It creates a wall "
"between signing you in and what you do once you're there. The history of "
"what sites you visit is stored only on your own computer."
msgstr ""
"Persona 只是連結您登入過程的一座橋樑,不會追蹤您在網路上的行為。您的網頁瀏覽"

#: resources/views/about.ejs:51
msgid "Persona for developers"
msgstr "Persona 的開發人員資訊"

You can view the complete zh_TW PO file, to get a better idea.

Create a locale

The Gettext tool msginit is used to create an empty PO file for a target locale, based on our POT file.

$ for l in en_US de es; do
    mkdir -p locale/${l}/LC_MESSAGES/
    msginit --input=./locale/templates/LC_MESSAGES/messages.pot 
            -l ${l}

We can see that we’ve created English, German, and Spanish PO files.

PO files

So we’ve extracted our Strings and created a bunch of locales.

Here is a sample file system layout:


You can give your localizers access to this part of your codebase. The Spanish team will need access to locale/es/LC_MESSAGES/messages.po for example. If you have a really big team, you might have es-ES for Spain’s Spanish and es-AR for Argentinian Spanish, instead of just a base es for all Spanish locales.

You can grow the number of locales over time.

Merge String changes

Release after release, you’ll add new Strings and change or delete others. You’ll need to update all of the PO files with these changes.

Gettext has powerful tools to make this easy.

We provide a wrapper shell script called merge-po.sh which uses GNU Gettext’s msgmerge under the covers.

Let’s put the i18n-abide tools in our path:

$ export PATH=$PATH:node_modules/i18n-abide/bin

And run a String merge:

$ ./node_modules/.bin/extract-pot --locale locale .
$ merge_po.sh ./locale

Just like the first time… extract-pot grabs all the Strings and updates the POT file. Next merge_po.sh updates each locale’s PO file to match our codebase. You can now ask your L10n teams to localize any new or changed Strings.

Gettext versus Not Invented Here

It is easy enough to throw out Gettext and re-invent the wheel using a new JSON format. This is the strategy that most node modules take.
If you have a healthy application, as you add locales and develop new features, you will find yourself frustrated by a thousand paper cuts.
Without merge_po.sh, you’ll have to write your own merge tools. This is because if you have 30 locales, you’ll need to update 30 JSON files without losing the work they’ve already done.

Gettext offers a powerful merge feature, which will save us many painful hours of coordination.

Wrapping Up

Now that we have various catalogs of strings in a po file per locale, we can hand these off to our localization teams.

It is always a good idea to talk to the localizers before you start the extract / merge steps. Give them a heads up on when the PO files will be ready, how many strings they have, and when you’d like to have the localization finished by. Also, you can read Gettext tutorials, as they are all compatible with our setup.

Okay, go get your Strings translated and in the next installment, we’ll put them to work!

Previous articles in the series

This was part ten in a series with a total of 12 posts about Node.js. The previous ones are:

About Austin King

Seattle based non-dogmatic Artist / Programmer type human. Rogue web developer with the Apps Engineering team. Spell check is for the week.

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About Robert Nyman [Editor emeritus]

Technical Evangelist & Editor of Mozilla Hacks. Gives talks & blogs about HTML5, JavaScript & the Open Web. Robert is a strong believer in HTML5 and the Open Web and has been working since 1999 with Front End development for the web - in Sweden and in New York City. He regularly also blogs at http://robertnyman.com and loves to travel and meet people.

More articles by Robert Nyman [Editor emeritus]…