==================== Internationalization ==================== Django has full support for internationalization of text in code and templates. Here's how it works. Overview ======== The goal of internationalization is to allow a single Web application to offer its content and functionality in multiple languages. You, the Django developer, can accomplish this goal by adding a minimal amount of hooks to your Python code and templates. These hooks are called **translation strings**. They tell Django: "This text should be translated into the end user's language, if a translation for this text is available in that language." Django takes care of using these hooks to translate Web apps, on the fly, according to users' language preferences. Essentially, Django does two things: * It lets developers and template authors specify which parts of their apps should be translatable. * It uses these hooks to translate Web apps for particular users according to their language preferences. How to internationalize your app: in three steps ------------------------------------------------ 1. Embed translation strings in your Python code and templates. 2. Get translations for those strings, in whichever languages you want to support. 3. Activate the locale middleware in your Django settings. .. admonition:: Behind the scenes Django's translation machinery uses the standard ``gettext`` module that comes with Python. If you don't need internationalization ====================================== Django's internationalization hooks are on by default, and that means there's a bit of i18n-related overhead in certain places of the framework. If you don't use internationalization, you should take the two seconds to set ``USE_I18N = False`` in your settings file. If ``USE_I18N`` is set to ``False``, then Django will make some optimizations so as not to load the internationalization machinery. See the `documentation for USE_I18N`_. .. _documentation for USE_I18N: http://www.djangoproject.com/documentation/settings/#use-i18n How to specify translation strings ================================== Translation strings specify "This text should be translated." These strings can appear in your Python code and templates. It's your responsibility to mark translatable strings; the system can only translate strings it knows about. In Python code -------------- Standard translation ~~~~~~~~~~~~~~~~~~~~ Specify a translation string by using the function ``_()``. (Yes, the name of the function is the "underscore" character.) This function is available globally in any Python module; you don't have to import it. In this example, the text ``"Welcome to my site."`` is marked as a translation string:: def my_view(request): output = _("Welcome to my site.") return HttpResponse(output) The function ``django.utils.translation.gettext()`` is identical to ``_()``. This example is identical to the previous one:: from django.utils.translation import gettext def my_view(request): output = gettext("Welcome to my site.") return HttpResponse(output) Translation works on computed values. This example is identical to the previous two:: def my_view(request): words = ['Welcome', 'to', 'my', 'site.'] output = _(' '.join(words)) return HttpResponse(output) Translation works on variables. Again, here's an identical example:: def my_view(request): sentence = 'Welcome to my site.' output = _(sentence) return HttpResponse(output) (The caveat with using variables or computed values, as in the previous two examples, is that Django's translation-string-detecting utility, ``make-messages.py``, won't be able to find these strings. More on ``make-messages`` later.) The strings you pass to ``_()`` or ``gettext()`` can take placeholders, specified with Python's standard named-string interpolation syntax. Example:: def my_view(request, n): output = _('%(name)s is my name.') % {'name': n} return HttpResponse(output) This technique lets language-specific translations reorder the placeholder text. For example, an English translation may be ``"Adrian is my name."``, while a Spanish translation may be ``"Me llamo Adrian."`` -- with the placeholder (the name) placed after the translated text instead of before it. For this reason, you should use named-string interpolation (e.g., ``%(name)s``) instead of positional interpolation (e.g., ``%s`` or ``%d``). If you used positional interpolation, translations wouldn't be able to reorder placeholder text. Marking strings as no-op ~~~~~~~~~~~~~~~~~~~~~~~~ Use the function ``django.utils.translation.gettext_noop()`` to mark a string as a translation string without translating it. The string is later translated from a variable. Use this if you have constant strings that should be stored in the source language because they are exchanged over systems or users -- such as strings in a database -- but should be translated at the last possible point in time, such as when the string is presented to the user. Lazy translation ~~~~~~~~~~~~~~~~ Use the function ``django.utils.translation.gettext_lazy()`` to translate strings lazily -- when the value is accessed rather than when the ``gettext_lazy()`` function is called. For example, to translate a model's ``help_text``, do the following:: from django.utils.translation import gettext_lazy class MyThing(models.Model): name = models.CharField(help_text=gettext_lazy('This is the help text')) In this example, ``gettext_lazy()`` stores a lazy reference to the string -- not the actual translation. The translation itself will be done when the string is used in a string context, such as template rendering on the Django admin site. If you don't like the verbose name ``gettext_lazy``, you can just alias it as ``_`` (underscore), like so:: from django.utils.translation import gettext_lazy as _ class MyThing(models.Model): name = models.CharField(help_text=_('This is the help text')) Always use lazy translations in `Django models`_. And it's a good idea to add translations for the field names and table names, too. This means writing explicit ``verbose_name`` and ``verbose_name_plural`` options in the ``Meta`` class, though:: from django.utils.translation import gettext_lazy as _ class MyThing(models.Model): name = models.CharField(_('name'), help_text=_('This is the help text')) class Meta: verbose_name = _('my thing') verbose_name_plural = _('mythings') .. _Django models: http://www.djangoproject.com/documentation/model_api/ Pluralization ~~~~~~~~~~~~~ Use the function ``django.utils.translation.ngettext()`` to specify pluralized messages. Example:: from django.utils.translation import ngettext def hello_world(request, count): page = ngettext('there is %(count)d object', 'there are %(count)d objects', count) % { 'count': count, } return HttpResponse(page) ``ngettext`` takes three arguments: the singular translation string, the plural translation string and the number of objects (which is passed to the translation languages as the ``count`` variable). In template code ---------------- Using translations in `Django templates`_ uses two template tags and a slightly different syntax than in Python code. To give your template access to these tags, put ``{% load i18n %}`` toward the top of your template. The ``{% trans %}`` template tag translates a constant string or a variable content:: {% trans "This is the title." %} If you only want to mark a value for translation, but translate it later from a variable, use the ``noop`` option:: {% trans "value" noop %} It's not possible to use template variables in ``{% trans %}`` -- only constant strings, in single or double quotes, are allowed. If your translations require variables (placeholders), use ``{% blocktrans %}``. Example:: {% blocktrans %}This will have {{ value }} inside.{% endblocktrans %} To translate a template expression -- say, using template filters -- you need to bind the expression to a local variable for use within the translation block:: {% blocktrans with value|filter as myvar %} This will have {{ myvar }} inside. {% endblocktrans %} If you need to bind more than one expression inside a ``blocktrans`` tag, separate the pieces with ``and``:: {% blocktrans with book|title as book_t and author|title as author_t %} This is {{ book_t }} by {{ author_t }} {% endblocktrans %} To pluralize, specify both the singular and plural forms with the ``{% plural %}`` tag, which appears within ``{% blocktrans %}`` and ``{% endblocktrans %}``. Example:: {% blocktrans count list|count as counter %} There is only one {{ name }} object. {% plural %} There are {{ counter }} {{ name }} objects. {% endblocktrans %} Internally, all block and inline translations use the appropriate ``gettext`` / ``ngettext`` call. Each ``RequestContext`` has access to two translation-specific variables: * ``LANGUAGES`` is a list of tuples in which the first element is the language code and the second is the language name (in that language). * ``LANGUAGE_CODE`` is the current user's preferred language, as a string. Example: ``en-us``. (See "How language preference is discovered", below.) * ``LANGUAGE_BIDI`` is the current language's direction. If True, it's a right-to-left language, e.g: Hebrew, Arabic. If False it's a left-to-right language, e.g: English, French, German etc. If you don't use the ``RequestContext`` extension, you can get those values with three tags:: {% get_current_language as LANGUAGE_CODE %} {% get_available_languages as LANGUAGES %} {% get_current_language_bidi as LANGUAGE_BIDI %} These tags also require a ``{% load i18n %}``. Translation hooks are also available within any template block tag that accepts constant strings. In those cases, just use ``_()`` syntax to specify a translation string. Example:: {% some_special_tag _("Page not found") value|yesno:_("yes,no") %} In this case, both the tag and the filter will see the already-translated string, so they don't need to be aware of translations. .. _Django templates: http://www.djangoproject.com/documentation/templates_python/ How to create language files ============================ Once you've tagged your strings for later translation, you need to write (or obtain) the language translations themselves. Here's how that works. Message files ------------- The first step is to create a **message file** for a new language. A message file is a plain-text file, representing a single language, that contains all available translation strings and how they should be represented in the given language. Message files have a ``.po`` file extension. Django comes with a tool, ``bin/make-messages.py``, that automates the creation and upkeep of these files. To create or update a message file, run this command:: bin/make-messages.py -l de ...where ``de`` is the language code for the message file you want to create. The language code, in this case, is in locale format. For example, it's ``pt_BR`` for Brazilian and ``de_AT`` for Austrian German. The script should be run from one of three places: * The root ``django`` directory (not a Subversion checkout, but the one that is linked-to via ``$PYTHONPATH`` or is located somewhere on that path). * The root directory of your Django project. * The root directory of your Django app. The script runs over the entire Django source tree and pulls out all strings marked for translation. It creates (or updates) a message file in the directory ``conf/locale``. In the ``de`` example, the file will be ``conf/locale/de/LC_MESSAGES/django.po``. If run over your project source tree or your application source tree, it will do the same, but the location of the locale directory is ``locale/LANG/LC_MESSAGES`` (note the missing ``conf`` prefix). .. admonition:: No gettext? If you don't have the ``gettext`` utilities installed, ``make-messages.py`` will create empty files. If that's the case, either install the ``gettext`` utilities or just copy the English message file (``conf/locale/en/LC_MESSAGES/django.po``) and use it as a starting point; it's just an empty translation file. The format of ``.po`` files is straightforward. Each ``.po`` file contains a small bit of metadata, such as the translation maintainer's contact information, but the bulk of the file is a list of **messages** -- simple mappings between translation strings and the actual translated text for the particular language. For example, if your Django app contained a translation string for the text ``"Welcome to my site."``, like so:: _("Welcome to my site.") ...then ``make-messages.py`` will have created a ``.po`` file containing the following snippet -- a message:: #: path/to/python/module.py:23 msgid "Welcome to my site." msgstr "" A quick explanation: * ``msgid`` is the translation string, which appears in the source. Don't change it. * ``msgstr`` is where you put the language-specific translation. It starts out empty, so it's your responsibility to change it. Make sure you keep the quotes around your translation. * As a convenience, each message includes the filename and line number from which the translation string was gleaned. Long messages are a special case. There, the first string directly after the ``msgstr`` (or ``msgid``) is an empty string. Then the content itself will be written over the next few lines as one string per line. Those strings are directly concatenated. Don't forget trailing spaces within the strings; otherwise, they'll be tacked together without whitespace! .. admonition:: Mind your charset When creating a ``.po`` file with your favorite text editor, first edit the charset line (search for ``"CHARSET"``) and set it to the charset you'll be using to edit the content. Generally, utf-8 should work for most languages, but ``gettext`` should handle any charset you throw at it. To reexamine all source code and templates for new translation strings and update all message files for **all** languages, run this:: make-messages.py -a Compiling message files ----------------------- After you create your message file -- and each time you make changes to it -- you'll need to compile it into a more efficient form, for use by ``gettext``. Do this with the ``bin/compile-messages.py`` utility. This tool runs over all available ``.po`` files and creates ``.mo`` files, which are binary files optimized for use by ``gettext``. In the same directory from which you ran ``make-messages.py``, run ``compile-messages.py`` like this:: bin/compile-messages.py That's it. Your translations are ready for use. .. admonition:: A note to translators If you've created a translation in a language Django doesn't yet support, please let us know! See `Submitting and maintaining translations`_ for the steps to take. .. _Submitting and maintaining translations: http://www.djangoproject.com/documentation/contributing/ How Django discovers language preference ======================================== Once you've prepared your translations -- or, if you just want to use the translations that come with Django -- you'll just need to activate translation for your app. Behind the scenes, Django has a very flexible model of deciding which language should be used -- installation-wide, for a particular user, or both. To set an installation-wide language preference, set ``LANGUAGE_CODE`` in your `settings file`_. Django uses this language as the default translation -- the final attempt if no other translator finds a translation. If all you want to do is run Django with your native language, and a language file is available for your language, all you need to do is set ``LANGUAGE_CODE``. If you want to let each individual user specify which language he or she prefers, use ``LocaleMiddleware``. ``LocaleMiddleware`` enables language selection based on data from the request. It customizes content for each user. To use ``LocaleMiddleware``, add ``'django.middleware.locale.LocaleMiddleware'`` to your ``MIDDLEWARE_CLASSES`` setting. Because middleware order matters, you should follow these guidelines: * Make sure it's one of the first middlewares installed. * It should come after ``SessionMiddleware``, because ``LocaleMiddleware`` makes use of session data. * If you use ``CacheMiddleware``, put ``LocaleMiddleware`` after it. For example, your ``MIDDLEWARE_CLASSES`` might look like this:: MIDDLEWARE_CLASSES = ( 'django.contrib.sessions.middleware.SessionMiddleware', 'django.middleware.locale.LocaleMiddleware', 'django.middleware.common.CommonMiddleware', ) (For more on middleware, see the `middleware documentation`_.) ``LocaleMiddleware`` tries to determine the user's language preference by following this algorithm: * First, it looks for a ``django_language`` key in the the current user's `session`_. * Failing that, it looks for a cookie called ``django_language``. * Failing that, it looks at the ``Accept-Language`` HTTP header. This header is sent by your browser and tells the server which language(s) you prefer, in order by priority. Django tries each language in the header until it finds one with available translations. * Failing that, it uses the global ``LANGUAGE_CODE`` setting. Notes: * In each of these places, the language preference is expected to be in the standard language format, as a string. For example, Brazilian is ``pt-br``. * If a base language is available but the sublanguage specified is not, Django uses the base language. For example, if a user specifies ``de-at`` (Austrian German) but Django only has ``de`` available, Django uses ``de``. * Only languages listed in the `LANGUAGES setting`_ can be selected. If you want to restrict the language selection to a subset of provided languages (because your application doesn't provide all those languages), set ``LANGUAGES`` to a list of languages. For example:: LANGUAGES = ( ('de', _('German')), ('en', _('English')), ) This example restricts languages that are available for automatic selection to German and English (and any sublanguage, like de-ch or en-us). .. _LANGUAGES setting: http://www.djangoproject.com/documentation/settings/#languages * If you define a custom ``LANGUAGES`` setting, as explained in the previous bullet, it's OK to mark the languages as translation strings -- but use a "dummy" ``gettext()`` function, not the one in ``django.utils.translation``. You should *never* import ``django.utils.translation`` from within your settings file, because that module in itself depends on the settings, and that would cause a circular import. The solution is to use a "dummy" ``gettext()`` function. Here's a sample settings file:: gettext = lambda s: s LANGUAGES = ( ('de', gettext('German')), ('en', gettext('English')), ) With this arrangement, ``make-messages.py`` will still find and mark these strings for translation, but the translation won't happen at runtime -- so you'll have to remember to wrap the languages in the *real* ``gettext()`` in any code that uses ``LANGUAGES`` at runtime. * The ``LocaleMiddleware`` can only select languages for which there is a Django-provided base translation. If you want to provide translations for your application that aren't already in the set of translations in Django's source tree, you'll want to provide at least basic translations for that language. For example, Django uses technical message IDs to translate date formats and time formats -- so you will need at least those translations for the system to work correctly. A good starting point is to copy the English ``.po`` file and to translate at least the technical messages -- maybe the validator messages, too. Technical message IDs are easily recognized; they're all upper case. You don't translate the message ID as with other messages, you provide the correct local variant on the provided English value. For example, with ``DATETIME_FORMAT`` (or ``DATE_FORMAT`` or ``TIME_FORMAT``), this would be the format string that you want to use in your language. The format is identical to the format strings used by the ``now`` template tag. Once ``LocaleMiddleware`` determines the user's preference, it makes this preference available as ``request.LANGUAGE_CODE`` for each `request object`_. Feel free to read this value in your view code. Here's a simple example:: def hello_world(request, count): if request.LANGUAGE_CODE == 'de-at': return HttpResponse("You prefer to read Austrian German.") else: return HttpResponse("You prefer to read another language.") Note that, with static (middleware-less) translation, the language is in ``settings.LANGUAGE_CODE``, while with dynamic (middleware) translation, it's in ``request.LANGUAGE_CODE``. .. _settings file: http://www.djangoproject.com/documentation/settings/ .. _middleware documentation: http://www.djangoproject.com/documentation/middleware/ .. _session: http://www.djangoproject.com/documentation/sessions/ .. _request object: http://www.djangoproject.com/documentation/request_response/#httprequest-objects The ``set_language`` redirect view ================================== As a convenience, Django comes with a view, ``django.views.i18n.set_language``, that sets a user's language preference and redirects back to the previous page. Activate this view by adding the following line to your URLconf:: (r'^i18n/', include('django.conf.urls.i18n')), (Note that this example makes the view available at ``/i18n/setlang/``.) The view expects to be called via the ``GET`` method, with a ``language`` parameter set in the query string. If session support is enabled, the view saves the language choice in the user's session. Otherwise, it saves the language choice in a ``django_language`` cookie. After setting the language choice, Django redirects the user, following this algorithm: * Django looks for a ``next`` parameter in the query string. * If that doesn't exist, or is empty, Django tries the URL in the ``Referer`` header. * If that's empty -- say, if a user's browser suppresses that header -- then the user will be redirected to ``/`` (the site root) as a fallback. Here's example HTML template code::
Using translations in your own projects ======================================= Django looks for translations by following this algorithm: * First, it looks for a ``locale`` directory in the application directory of the view that's being called. If it finds a translation for the selected language, the translation will be installed. * Next, it looks for a ``locale`` directory in the project directory. If it finds a translation, the translation will be installed. * Finally, it checks the base translation in ``django/conf/locale``. This way, you can write applications that include their own translations, and you can override base translations in your project path. Or, you can just build a big project out of several apps and put all translations into one big project message file. The choice is yours. .. note:: If you're using manually configured settings, as described in the `settings documentation`_, the ``locale`` directory in the project directory will not be examined, since Django loses the ability to work out the location of the project directory. (Django normally uses the location of the settings file to determine this, and a settings file doesn't exist if you're manually configuring your settings.) .. _settings documentation: http://www.djangoproject.com/documentation/settings/#using-settings-without-the-django-settings-module-environment-variable All message file repositories are structured the same way. They are: * ``$APPPATH/locale//LC_MESSAGES/django.(po|mo)`` * ``$PROJECTPATH/locale//LC_MESSAGES/django.(po|mo)`` * All paths listed in ``LOCALE_PATHS`` in your settings file are searched in that order for ``/LC_MESSAGES/django.(po|mo)`` * ``$PYTHONPATH/django/conf/locale//LC_MESSAGES/django.(po|mo)`` To create message files, you use the same ``make-messages.py`` tool as with the Django message files. You only need to be in the right place -- in the directory where either the ``conf/locale`` (in case of the source tree) or the ``locale/`` (in case of app messages or project messages) directory are located. And you use the same ``compile-messages.py`` to produce the binary ``django.mo`` files that are used by ``gettext``. Application message files are a bit complicated to discover -- they need the ``LocaleMiddleware``. If you don't use the middleware, only the Django message files and project message files will be processed. Finally, you should give some thought to the structure of your translation files. If your applications need to be delivered to other users and will be used in other projects, you might want to use app-specific translations. But using app-specific translations and project translations could produce weird problems with ``make-messages``: ``make-messages`` will traverse all directories below the current path and so might put message IDs into the project message file that are already in application message files. The easiest way out is to store applications that are not part of the project (and so carry their own translations) outside the project tree. That way, ``make-messages`` on the project level will only translate strings that are connected to your explicit project and not strings that are distributed independently. Translations and JavaScript =========================== Adding translations to JavaScript poses some problems: * JavaScript code doesn't have access to a ``gettext`` implementation. * JavaScript code doesn't have access to .po or .mo files; they need to be delivered by the server. * The translation catalogs for JavaScript should be kept as small as possible. Django provides an integrated solution for these problems: It passes the translations into JavaScript, so you can call ``gettext``, etc., from within JavaScript. The ``javascript_catalog`` view ------------------------------- The main solution to these problems is the ``javascript_catalog`` view, which sends out a JavaScript code library with functions that mimic the ``gettext`` interface, plus an array of translation strings. Those translation strings are taken from the application, project or Django core, according to what you specify in either the {{{info_dict}}} or the URL. You hook it up like this:: js_info_dict = { 'packages': ('your.app.package',), } urlpatterns = patterns('', (r'^jsi18n/$', 'django.views.i18n.javascript_catalog', js_info_dict), ) Each string in ``packages`` should be in Python dotted-package syntax (the same format as the strings in ``INSTALLED_APPS``) and should refer to a package that contains a ``locale`` directory. If you specify multiple packages, all those catalogs are merged into one catalog. This is useful if you have JavaScript that uses strings from different applications. You can make the view dynamic by putting the packages into the URL pattern:: urlpatterns = patterns('', (r'^jsi18n/(?P\S+?)/$, 'django.views.i18n.javascript_catalog'), ) With this, you specify the packages as a list of package names delimited by '+' signs in the URL. This is especially useful if your pages use code from different apps and this changes often and you don't want to pull in one big catalog file. As a security measure, these values can only be either ``django.conf`` or any package from the ``INSTALLED_APPS`` setting. Using the JavaScript translation catalog ---------------------------------------- To use the catalog, just pull in the dynamically generated script like this:: This is how the admin fetches the translation catalog from the server. When the catalog is loaded, your JavaScript code can use the standard ``gettext`` interface to access it:: document.write(gettext('this is to be translated')); There even is a ``ngettext`` interface and a string interpolation function:: d = { count: 10 }; s = interpolate(ngettext('this is %(count)s object', 'this are %(count)s objects', d.count), d); The ``interpolate`` function supports both positional interpolation and named interpolation. So the above could have been written as:: s = interpolate(ngettext('this is %s object', 'this are %s objects', 11), [11]); The interpolation syntax is borrowed from Python. You shouldn't go over the top with string interpolation, though: this is still JavaScript, so the code will have to do repeated regular-expression substitutions. This isn't as fast as string interpolation in Python, so keep it to those cases where you really need it (for example, in conjunction with ``ngettext`` to produce proper pluralizations). Creating JavaScript translation catalogs ---------------------------------------- You create and update the translation catalogs the same way as the other Django translation catalogs -- with the {{{make-messages.py}}} tool. The only difference is you need to provide a ``-d djangojs`` parameter, like this:: make-messages.py -d djangojs -l de This would create or update the translation catalog for JavaScript for German. After updating translation catalogs, just run ``compile-messages.py`` the same way as you do with normal Django translation catalogs. Specialities of Django translation ================================== If you know ``gettext``, you might note these specialities in the way Django does translation: * The string domain is ``django`` or ``djangojs``. The string domain is used to differentiate between different programs that store their data in a common message-file library (usually ``/usr/share/locale/``). The ``django`` domain is used for python and template translation strings and is loaded into the global translation catalogs. The ``djangojs`` domain is only used for JavaScript translation catalogs to make sure that those are as small as possible. * Django only uses ``gettext`` and ``gettext_noop``. That's because Django always uses ``DEFAULT_CHARSET`` strings internally. There isn't much use in using ``ugettext``, because you'll always need to produce utf-8 anyway. * Django doesn't use ``xgettext`` alone. It uses Python wrappers around ``xgettext`` and ``msgfmt``. That's mostly for convenience.