====================

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`_.

You'll probably also want to remove ``'django.core.context_processors.i18n'``

from your ``TEMPLATE_CONTEXT_PROCESSORS`` setting.

.. _documentation for USE_I18N: ../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: ../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::

    <title>{% trans "This is the title." %}</title>

If you only want to mark a value for translation, but translate it later from a

variable, use the ``noop`` option::

    <title>{% trans "value" noop %}</title>

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: ../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.

.. admonition:: Locale restrictions

    Django does not support localizing your application into a locale for

    which Django itself has not been translated. In this case, it will ignore

    your translation files. If you were to try this and Django supported it,

    you would inevitably see a mixture of translated strings (from your

    application) and English strings (from Django itself). If you want to

    support a locale for your application that is not already part of

    Django, you'll need to make at least a minimal translation of the Django

    core.

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: ../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: ../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.