==========================
Deployment of translations
==========================

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
:setting:`USE_I18N = False <USE_I18N>` in your settings file. If
:setting:`USE_I18N` is set to ``False``, then Django will make some
optimizations so as not to load the internationalization machinery.

You'll probably also want to remove ``'django.core.context_processors.i18n'``
from your ``TEMPLATE_CONTEXT_PROCESSORS`` setting.

.. note::

    There is also an independent but related :setting:`USE_L10N` setting that
    controls if Django should implement format localization.

    If :setting:`USE_L10N` is set to ``True``, Django will handle numbers times,
    and dates in the format of the current locale. That includes representation
    of these field types on templates and allowed input formats for dates,
    times on model forms.

    See :ref:`format-localization` for more details.

If you do need internationalization
===================================

.. _how-django-discovers-language-preference:

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 :setting:`LANGUAGE_CODE`.
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 it, 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 :doc:`middleware documentation
</topics/http/middleware>`.)

``LocaleMiddleware`` tries to determine the user's language preference by
following this algorithm:

    * First, it looks for a ``django_language`` key in the current user's
      session.

    * Failing that, it looks for a cookie.

      The name of the cookie used is set by the ``LANGUAGE_COOKIE_NAME``
      setting. (The default name is ``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.

.. _locale-middleware-notes:

Notes:

    * In each of these places, the language preference is expected to be in the
      standard :term:`language format<language code>`, as a string. For example,
      Brazilian Portuguese 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 :setting:`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).

    * 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" ``ugettext()`` 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" ``ugettext()`` function. Here's a sample
      settings file::

          ugettext = lambda s: s

          LANGUAGES = (
              ('de', ugettext('German')),
              ('en', ugettext('English')),
          )

      With this arrangement, ``django-admin.py makemessages`` 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* ``ugettext()`` 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 a basic
      one as described in the :ref:`Locale restrictions<locale-restrictions>`
      note.

Once ``LocaleMiddleware`` determines the user's preference, it makes this
preference available as ``request.LANGUAGE_CODE`` for each
:class:`~django.http.HttpRequest`. 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: ../settings/
.. _middleware documentation: ../middleware/
.. _session: ../sessions/
.. _request object: ../request_response/#httprequest-objects

How Django discovers translations
---------------------------------

As described in :ref:`using-translations-in-your-own-projects`,
at runtime, Django looks for translations by following this algorithm:

    * First, it looks for a ``locale`` directory in the directory containing
      your settings file.
    * Second, it looks for a ``locale`` directory in the project directory.
    * Third, it looks for a ``locale`` directory in each of the installed apps.
      It does this in the reverse order of INSTALLED_APPS
    * Finally, it checks the Django-provided base translation in
      ``django/conf/locale``.

In all cases the name of the directory containing the translation is expected to
be named using :term:`locale name` notation. E.g. ``de``, ``pt_BR``, ``es_AR``,
etc.
