Tutorials - internationalizing your app

As a developer, you probably want to see your apps in many hands. One way to make it happen is to enable your application for translation.

With minimal effort, you can mark your application strings for translation, expose them to community translators and integrate these translations into your package. The translations building process is handled by the SDK itself and if you happen to use Launchpad, translators will quickly see your project and help you, but you still need to mark your user-visible strings as translatable. Let's get started.


A few terms you need to understand before diving in.

  • Gettext: the technology used by Ubuntu to translate applications
  • Internationalization (i18n): what you will be doing in your app to enable translations
  • Localization (l10n): what translators do
  • User locale: for most cases, you can think of it as the language the user has chosen for the UI of their system. However, locale is the broader term that includes the group of settings associated with a particular localized configuration: language, date/time format, currency, etc.
  • POT files: template files containing all your application strings, exposed to translators. There is generally only one and it is also known as “Translation template.”
  • PO files: what translators (or an online translation system) produce, they contain translated strings based on a POT file. There is a .po file for each language a translation is available in, and the files are commonly called the “Translations”.
  • MO files: binary files loaded in your app at runtime, built from PO files. These are the only files that your packaged app will need to ship to use translations.

Getting started

First, make sure you are up-to-date on what an SDK app needs in term of preparation, for example, adding click targets to build for a specific device.

During this tutorial, we are going to use a sample app and see what it takes to get a translated version into users hands. You can grab the code by running:

bzr branch lp:~davidc3/howmanyapples/no-i18n

Or read it online ›

Or simply use one of your existing projects and try to follow along (Note: make sure to update your project to the latest SDK template by following these steps).

This tutorial is generic, so that in practice you can apply the steps to any QML project that uses the Ubuntu UI Toolkit.

Before getting into the code, let's have a look at some common methods.

Marking a string for translation

The SDK provides an i18n API with a very straightforward way to do that. Marking a string is as simple as calling i18n.tr(string).

For example:

Label {
    text:i18n.tr("My Label")

Managing plural forms

In many latin languages such as english or french, putting a sentence to the plural form is - most of the time - simply a matter of adding an “s”. But this is not the case in a lot of languages, for example, Arabic has six different plural forms, Croatian and Russian have three, etc.

The i18n API gives you a clean solution:

i18n.tr("%1 cat", "%1 cats", nb_of_cats).arg(nb_of_cats)

In the example, the first argument to i18n.tr() is the english singular form, the second one is the English plural, then comes the integer which will trigger the change of form. They will be used to generate a translation template suited to all languages.

Working with the plural form and i18n has been extensively documented, for more information on that topic, such as a guide to design a correct plural form, have a look here.

Providing context

Translators only see the string enabled for translation, not the code around, which means they can be confused by the exact meaning or context of a string, and most of the time, they don’t see the app in action at this specific step. Don’t let them in the dark and make sure they fully understand what the purpose of your strings are.

You can do that by adding translators comments to your code. Above any translatable string, you can add a special comment starting with “TRANSLATORS:”. Note that the default Ubuntu SDK setup will only pick up translators comment starting this way. For example

// TRANSLATORS: %1 refers to the amount of animals, %2 to the species
text: i18n.tr(Do you want to buy %1 more %2?).arg(nb_animals).arg(species)

In practice

If you haven't already, download the source of the sample app by opening a terminal with Ctrl+Alt+t and running

bzr branch lp:~davidc3/howmanyapples/no-i18n

Open it with the SDK

cd no-i18n
ubuntu-sdk .

It will open the editor. Click on Main.qml in the left column. The file should look like this: http://bazaar.launchpad.net/~davidc3/howmanyapples/no-i18n/view/head:/Main.qml

Now, try to change all user-visible strings to i18n.tr(string)

Hint: They are located at lines 27, 47 49, 51, 53, 74, 92, 108, 132 & 140

Try to run the app with Ctrl+R, to see if it launches. If it doesn't, make sure to check the error log for typos you could have made.

That's it, you know how to internationalize!

But that's not all, you can see that at lines 74 and 92, you have the potential to use the plurals method

Change line 74 to:

text:i18n.tr("You are making %1 for %2 guest",
            "You are making %1 for %2 guests",

The third argument of the tr() method (here "guests") is the value that triggers the change to the plural form. Therefore, at line 92, you can do:

text:i18n.tr("You will need %1 apple for this recipe", "You will need %1 apples for this recipe", apples).arg(apples)

Other internationalization features

In this app, you also have the opportunity to use localized currencies, with the toLocaleCurrencyString() method

Change line 108:

text: "This will cost you %1".arg(price)


text: i18n.tr("This will cost you %1").arg(Number(price).toLocaleCurrencyString(Qt.locale())

It will pick the correct currency symbol and the right number format depending on the locale.

This is a feature of the Locale QML Type, documented here, which provides a list of convenient methods for app developers: metric and imperial units formats, nativeCountryName, nativeLanguageName, dateFormat, timeFormat, etc.

The Date type is also worth looking into if your application is displaying dates or times. This will be the topic of another tutorial.

Let's have a look at the final internationalized version of our sample app

As you can see, I've also added a few translator comments. Make sure to use them for any strings needing context!

Building the POT file

The POT file will be located in a po/ folder in our app and will contain every string we have marked for translations (including translators comments).

The SDK automatically builds it during the build step of your application. When you run it, create your click package or click the build button, it generates or re-generates it.

If you use Launchpad to get your app translated collaboratively by a community of translators, the Translations page (https://translations.launchpad.net/<projectname>) will propose you to use this POT file for translations and automatically import available translations back in your project, as .po files, when they are available. Remember to add the .pot file to revision control and to set up your project fortranslations.

Building translations before publishing your app

Once translators have worked on your app, make sure you run a last bzr pull to get all the translations (.po files) from Launchpad before building the actual files (.mo) that will be shipped in your package.

Build your application one more time or simply create your click package from the Publish tab of the SDK to build your translations.

This creates binary .mo files from the .po files provided by translators. They will be loaded at runtime depending on the user locale.

That's it, you are ready to publish a multi-language QML app!

Shipping translations

Translations are included in your click package in share/locale/$lang/LC_MESSAGES/$appname.mo, if you have built your package outside of the SDK, make sure to check they are included in this path, or your app won’t be translated on users devices.

Testing your app in other languages

To evaluate the quality of your translations or just see how your UI looks in another language, the easiest way is to use your target device (phone, tablet, emulator…) and change its language from System Settings > Language & Text > Language.

There is more to internationalization

Some areas of i18n are not covered by this tutorial. For example, The SDK doesn’t automatically mark for translation the content of the .desktop file of your app (its name, description, etc.), which is handled separately by CMake. This will be the topic of a more general i18n guide, stay tuned!

Optional: Updating your project SDK template

From time to time, project templates provided by the SDK get updated. To get the changes needed for this tutorial (released end of April 2015), you need to update your project template manually. If your project as been created after this date, you don’t have anything to do.

  1. Make sure you have updated to the latest version of the Ubuntu SDK
  2. Rename your project folder to something else
  3. Create a new project with the SDK similar in all points to your original project
  4. Copy everything from your renamed project folder to the new one. Except the Makefile, .qmlproject and .qmlproject.user. Don't forget to copy your .bzr folder if you use bzr.