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580 lines
22 KiB
Plaintext
.. _topics-i18n-internationalization:
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====================
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Internationalization
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====================
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Overview
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========
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The goal of internationalization is to allow a single Web application to offer
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its content and functionality in multiple languages and locales.
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For text translations, you, the Django developer, can accomplish this goal by
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adding a minimal amount of hooks to your Python and templates. These hooks
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are called **translation strings**. They tell Django: "This text should be
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translated into the end user's language, if a translation for this text is
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available in that language." It's your responsibility to mark translatable
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strings; the system can only translate strings it knows about.
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Django takes care of using these hooks to translate Web apps, on the fly,
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according to users' language preferences.
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Specifying translation strings: In Python code
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==============================================
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Standard translation
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--------------------
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Specify a translation string by using the function ``ugettext()``. It's
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convention to import this as a shorter alias, ``_``, to save typing.
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.. note::
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Python's standard library ``gettext`` module installs ``_()`` into the
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global namespace, as an alias for ``gettext()``. In Django, we have chosen
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not to follow this practice, for a couple of reasons:
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1. For international character set (Unicode) support, ``ugettext()`` is
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more useful than ``gettext()``. Sometimes, you should be using
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``ugettext_lazy()`` as the default translation method for a particular
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file. Without ``_()`` in the global namespace, the developer has to
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think about which is the most appropriate translation function.
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2. The underscore character (``_``) is used to represent "the previous
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result" in Python's interactive shell and doctest tests. Installing a
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global ``_()`` function causes interference. Explicitly importing
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``ugettext()`` as ``_()`` avoids this problem.
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.. highlightlang:: python
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In this example, the text ``"Welcome to my site."`` is marked as a translation
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string::
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from django.utils.translation import ugettext as _
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def my_view(request):
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output = _("Welcome to my site.")
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return HttpResponse(output)
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Obviously, you could code this without using the alias. This example is
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identical to the previous one::
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from django.utils.translation import ugettext
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def my_view(request):
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output = ugettext("Welcome to my site.")
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return HttpResponse(output)
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Translation works on computed values. This example is identical to the previous
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two::
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def my_view(request):
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words = ['Welcome', 'to', 'my', 'site.']
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output = _(' '.join(words))
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return HttpResponse(output)
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Translation works on variables. Again, here's an identical example::
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def my_view(request):
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sentence = 'Welcome to my site.'
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output = _(sentence)
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return HttpResponse(output)
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(The caveat with using variables or computed values, as in the previous two
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examples, is that Django's translation-string-detecting utility,
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``django-admin.py makemessages``, won't be able to find these strings. More on
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``makemessages`` later.)
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The strings you pass to ``_()`` or ``ugettext()`` can take placeholders,
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specified with Python's standard named-string interpolation syntax. Example::
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def my_view(request, m, d):
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output = _('Today is %(month)s, %(day)s.') % {'month': m, 'day': d}
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return HttpResponse(output)
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This technique lets language-specific translations reorder the placeholder
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text. For example, an English translation may be ``"Today is November, 26."``,
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while a Spanish translation may be ``"Hoy es 26 de Noviembre."`` -- with the
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placeholders (the month and the day) with their positions swapped.
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For this reason, you should use named-string interpolation (e.g., ``%(day)s``)
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instead of positional interpolation (e.g., ``%s`` or ``%d``) whenever you
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have more than a single parameter. If you used positional interpolation,
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translations wouldn't be able to reorder placeholder text.
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Marking strings as no-op
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------------------------
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Use the function ``django.utils.translation.ugettext_noop()`` to mark a string
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as a translation string without translating it. The string is later translated
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from a variable.
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Use this if you have constant strings that should be stored in the source
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language because they are exchanged over systems or users -- such as strings in
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a database -- but should be translated at the last possible point in time, such
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as when the string is presented to the user.
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Pluralization
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-------------
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Use the function ``django.utils.translation.ungettext()`` to specify pluralized
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messages.
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``ungettext`` takes three arguments: the singular translation string, the plural
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translation string and the number of objects.
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This function is useful when you need your Django application to be localizable
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to languages where the number and complexity of `plural forms
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<http://www.gnu.org/software/gettext/manual/gettext.html#Plural-forms>`_ is
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greater than the two forms used in English ('object' for the singular and
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'objects' for all the cases where ``count`` is different from zero, irrespective
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of its value.)
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For example::
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from django.utils.translation import ungettext
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def hello_world(request, count):
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page = ungettext('there is %(count)d object', 'there are %(count)d objects', count) % {
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'count': count,
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}
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return HttpResponse(page)
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In this example the number of objects is passed to the translation languages as
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the ``count`` variable.
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Lets see a slightly more complex usage example::
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from django.utils.translation import ungettext
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count = Report.objects.count()
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if count == 1:
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name = Report._meta.verbose_name
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else:
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name = Report._meta.verbose_name_plural
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text = ungettext(
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'There is %(count)d %(name)s available.',
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'There are %(count)d %(name)s available.',
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count
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) % {
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'count': count,
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'name': name
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}
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Here we reuse localizable, hopefully already translated literals (contained in
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the ``verbose_name`` and ``verbose_name_plural`` model ``Meta`` options) for
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other parts of the sentence so all of it is consistently based on the
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cardinality of the elements at play.
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.. _pluralization-var-notes:
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.. note::
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When using this technique, make sure you use a single name for every
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extrapolated variable included in the literal. In the example above note how
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we used the ``name`` Python variable in both translation strings. This
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example would fail::
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from django.utils.translation import ungettext
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from myapp.models import Report
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count = Report.objects.count()
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d = {
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'count': count,
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'name': Report._meta.verbose_name
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'plural_name': Report._meta.verbose_name_plural
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}
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text = ungettext(
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'There is %(count)d %(name)s available.',
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'There are %(count)d %(plural_name)s available.',
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count
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) % d
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You would get a ``a format specification for argument 'name', as in
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'msgstr[0]', doesn't exist in 'msgid'`` error when running
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``django-admin.py compilemessages`` or a ``KeyError`` Python exception at
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runtime.
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.. _lazy-translations:
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Lazy translation
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----------------
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Use the function ``django.utils.translation.ugettext_lazy()`` to translate
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strings lazily -- when the value is accessed rather than when the
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``ugettext_lazy()`` function is called.
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For example, to translate a model's ``help_text``, do the following::
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from django.utils.translation import ugettext_lazy
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class MyThing(models.Model):
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name = models.CharField(help_text=ugettext_lazy('This is the help text'))
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In this example, ``ugettext_lazy()`` stores a lazy reference to the string --
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not the actual translation. The translation itself will be done when the string
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is used in a string context, such as template rendering on the Django admin
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site.
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The result of a ``ugettext_lazy()`` call can be used wherever you would use a
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unicode string (an object with type ``unicode``) in Python. If you try to use
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it where a bytestring (a ``str`` object) is expected, things will not work as
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expected, since a ``ugettext_lazy()`` object doesn't know how to convert
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itself to a bytestring. You can't use a unicode string inside a bytestring,
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either, so this is consistent with normal Python behavior. For example::
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# This is fine: putting a unicode proxy into a unicode string.
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u"Hello %s" % ugettext_lazy("people")
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# This will not work, since you cannot insert a unicode object
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# into a bytestring (nor can you insert our unicode proxy there)
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"Hello %s" % ugettext_lazy("people")
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If you ever see output that looks like ``"hello
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<django.utils.functional...>"``, you have tried to insert the result of
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``ugettext_lazy()`` into a bytestring. That's a bug in your code.
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If you don't like the verbose name ``ugettext_lazy``, you can just alias it as
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``_`` (underscore), like so::
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from django.utils.translation import ugettext_lazy as _
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class MyThing(models.Model):
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name = models.CharField(help_text=_('This is the help text'))
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Always use lazy translations in :ref:`Django models <topics-db-models>`.
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Field names and table names should be marked for translation (otherwise, they
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won't be translated in the admin interface). This means writing explicit
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``verbose_name`` and ``verbose_name_plural`` options in the ``Meta`` class,
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though, rather than relying on Django's default determination of
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``verbose_name`` and ``verbose_name_plural`` by looking at the model's class
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name::
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from django.utils.translation import ugettext_lazy as _
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class MyThing(models.Model):
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name = models.CharField(_('name'), help_text=_('This is the help text'))
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class Meta:
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verbose_name = _('my thing')
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verbose_name_plural = _('mythings')
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Working with lazy translation objects
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-------------------------------------
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.. highlightlang:: python
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Using ``ugettext_lazy()`` and ``ungettext_lazy()`` to mark strings in models
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and utility functions is a common operation. When you're working with these
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objects elsewhere in your code, you should ensure that you don't accidentally
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convert them to strings, because they should be converted as late as possible
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(so that the correct locale is in effect). This necessitates the use of a
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couple of helper functions.
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Joining strings: string_concat()
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~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
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Standard Python string joins (``''.join([...])``) will not work on lists
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containing lazy translation objects. Instead, you can use
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``django.utils.translation.string_concat()``, which creates a lazy object that
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concatenates its contents *and* converts them to strings only when the result
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is included in a string. For example::
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from django.utils.translation import string_concat
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...
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name = ugettext_lazy(u'John Lennon')
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instrument = ugettext_lazy(u'guitar')
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result = string_concat([name, ': ', instrument])
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In this case, the lazy translations in ``result`` will only be converted to
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strings when ``result`` itself is used in a string (usually at template
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rendering time).
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The allow_lazy() decorator
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~~~~~~~~~~~~~~~~~~~~~~~~~~
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Django offers many utility functions (particularly in ``django.utils``) that
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take a string as their first argument and do something to that string. These
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functions are used by template filters as well as directly in other code.
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If you write your own similar functions and deal with translations, you'll
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face the problem of what to do when the first argument is a lazy translation
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object. You don't want to convert it to a string immediately, because you might
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be using this function outside of a view (and hence the current thread's locale
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setting will not be correct).
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For cases like this, use the ``django.utils.functional.allow_lazy()``
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decorator. It modifies the function so that *if* it's called with a lazy
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translation as the first argument, the function evaluation is delayed until it
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needs to be converted to a string.
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For example::
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from django.utils.functional import allow_lazy
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def fancy_utility_function(s, ...):
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# Do some conversion on string 's'
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...
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fancy_utility_function = allow_lazy(fancy_utility_function, unicode)
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The ``allow_lazy()`` decorator takes, in addition to the function to decorate,
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a number of extra arguments (``*args``) specifying the type(s) that the
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original function can return. Usually, it's enough to include ``unicode`` here
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and ensure that your function returns only Unicode strings.
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Using this decorator means you can write your function and assume that the
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input is a proper string, then add support for lazy translation objects at the
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end.
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Specifying translation strings: In template code
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================================================
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.. highlightlang:: html+django
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Translations in :ref:`Django templates <topics-templates>` uses two template
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tags and a slightly different syntax than in Python code. To give your template
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access to these tags, put ``{% load i18n %}`` toward the top of your template.
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The ``{% trans %}`` template tag translates either a constant string
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(enclosed in single or double quotes) or variable content::
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<title>{% trans "This is the title." %}</title>
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<title>{% trans myvar %}</title>
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If the ``noop`` option is present, variable lookup still takes place but the
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translation is skipped. This is useful when "stubbing out" content that will
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require translation in the future::
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<title>{% trans "myvar" noop %}</title>
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Internally, inline translations use an ``ugettext`` call.
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It's not possible to mix a template variable inside a string within ``{% trans
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%}``. If your translations require strings with variables (placeholders), use
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``{% blocktrans %}``::
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{% blocktrans %}This string will have {{ value }} inside.{% endblocktrans %}
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To translate a template expression -- say, using template filters -- you need
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to bind the expression to a local variable for use within the translation
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block::
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{% blocktrans with value|filter as myvar %}
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This will have {{ myvar }} inside.
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{% endblocktrans %}
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If you need to bind more than one expression inside a ``blocktrans`` tag,
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separate the pieces with ``and``::
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{% blocktrans with book|title as book_t and author|title as author_t %}
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This is {{ book_t }} by {{ author_t }}
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{% endblocktrans %}
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To pluralize, specify both the singular and plural forms with the
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``{% plural %}`` tag, which appears within ``{% blocktrans %}`` and
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``{% endblocktrans %}``. Example::
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{% blocktrans count list|length as counter %}
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There is only one {{ name }} object.
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{% plural %}
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There are {{ counter }} {{ name }} objects.
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{% endblocktrans %}
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When you use the pluralization feature and bind additional values to local
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variables apart from the counter value that selects the translated literal to be
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used, have in mind that the ``blocktrans`` construct is internally converted
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to an ``ungettext`` call. This means the same :ref:`notes regarding ungettext
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variables <pluralization-var-notes>` apply.
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Each ``RequestContext`` has access to three translation-specific variables:
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* ``LANGUAGES`` is a list of tuples in which the first element is the
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:term:`language code` and the second is the language name (translated into
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the currently active locale).
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* ``LANGUAGE_CODE`` is the current user's preferred language, as a string.
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Example: ``en-us``. (See :ref:`how-django-discovers-language-preference`.)
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* ``LANGUAGE_BIDI`` is the current locale's direction. If True, it's a
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right-to-left language, e.g.: Hebrew, Arabic. If False it's a
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left-to-right language, e.g.: English, French, German etc.
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If you don't use the ``RequestContext`` extension, you can get those values with
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three tags::
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{% get_current_language as LANGUAGE_CODE %}
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{% get_available_languages as LANGUAGES %}
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{% get_current_language_bidi as LANGUAGE_BIDI %}
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These tags also require a ``{% load i18n %}``.
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Translation hooks are also available within any template block tag that accepts
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constant strings. In those cases, just use ``_()`` syntax to specify a
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translation string::
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{% some_special_tag _("Page not found") value|yesno:_("yes,no") %}
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In this case, both the tag and the filter will see the already-translated
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string, so they don't need to be aware of translations.
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.. note::
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In this example, the translation infrastructure will be passed the string
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``"yes,no"``, not the individual strings ``"yes"`` and ``"no"``. The
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translated string will need to contain the comma so that the filter
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parsing code knows how to split up the arguments. For example, a German
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translator might translate the string ``"yes,no"`` as ``"ja,nein"``
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(keeping the comma intact).
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.. _Django templates: ../templates_python/
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Specifying translation strings: In JavaScript code
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==================================================
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Adding translations to JavaScript poses some problems:
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* JavaScript code doesn't have access to a ``gettext`` implementation.
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* JavaScript code doesn't have access to .po or .mo files; they need to be
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delivered by the server.
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* The translation catalogs for JavaScript should be kept as small as
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possible.
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Django provides an integrated solution for these problems: It passes the
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translations into JavaScript, so you can call ``gettext``, etc., from within
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JavaScript.
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The ``javascript_catalog`` view
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-------------------------------
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The main solution to these problems is the ``javascript_catalog`` view, which
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sends out a JavaScript code library with functions that mimic the ``gettext``
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interface, plus an array of translation strings. Those translation strings are
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taken from the application, project or Django core, according to what you
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specify in either the info_dict or the URL.
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You hook it up like this::
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js_info_dict = {
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'packages': ('your.app.package',),
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}
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urlpatterns = patterns('',
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(r'^jsi18n/$', 'django.views.i18n.javascript_catalog', js_info_dict),
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)
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Each string in ``packages`` should be in Python dotted-package syntax (the
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same format as the strings in ``INSTALLED_APPS``) and should refer to a package
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that contains a ``locale`` directory. If you specify multiple packages, all
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those catalogs are merged into one catalog. This is useful if you have
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JavaScript that uses strings from different applications.
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You can make the view dynamic by putting the packages into the URL pattern::
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urlpatterns = patterns('',
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(r'^jsi18n/(?P<packages>\S+?)/$', 'django.views.i18n.javascript_catalog'),
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)
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With this, you specify the packages as a list of package names delimited by '+'
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signs in the URL. This is especially useful if your pages use code from
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different apps and this changes often and you don't want to pull in one big
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catalog file. As a security measure, these values can only be either
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``django.conf`` or any package from the ``INSTALLED_APPS`` setting.
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Using the JavaScript translation catalog
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----------------------------------------
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To use the catalog, just pull in the dynamically generated script like this::
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<script type="text/javascript" src={% url django.views.i18n.javascript_catalog %}"></script>
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This uses reverse URL lookup to find the URL of the JavaScript catalog view.
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When the catalog is loaded, your JavaScript code can use the standard
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``gettext`` interface to access it::
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document.write(gettext('this is to be translated'));
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|
There is also an ``ngettext`` interface::
|
|
|
|
var object_cnt = 1 // or 0, or 2, or 3, ...
|
|
s = ngettext('literal for the singular case',
|
|
'literal for the plural case', object_cnt);
|
|
|
|
and even a string interpolation function::
|
|
|
|
function interpolate(fmt, obj, named);
|
|
|
|
The interpolation syntax is borrowed from Python, so the ``interpolate``
|
|
function supports both positional and named interpolation:
|
|
|
|
* Positional interpolation: ``obj`` contains a JavaScript Array object
|
|
whose elements values are then sequentially interpolated in their
|
|
corresponding ``fmt`` placeholders in the same order they appear.
|
|
For example::
|
|
|
|
fmts = ngettext('There is %s object. Remaining: %s',
|
|
'There are %s objects. Remaining: %s', 11);
|
|
s = interpolate(fmts, [11, 20]);
|
|
// s is 'There are 11 objects. Remaining: 20'
|
|
|
|
* Named interpolation: This mode is selected by passing the optional
|
|
boolean ``named`` parameter as true. ``obj`` contains a JavaScript
|
|
object or associative array. For example::
|
|
|
|
d = {
|
|
count: 10
|
|
total: 50
|
|
};
|
|
|
|
fmts = ngettext('Total: %(total)s, there is %(count)s object',
|
|
'there are %(count)s of a total of %(total)s objects', d.count);
|
|
s = interpolate(fmts, d, true);
|
|
|
|
You shouldn't go over the top with string interpolation, though: this is still
|
|
JavaScript, so the code has to make 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).
|
|
|
|
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 ``POST`` method, with a ``language``
|
|
parameter set in request. If session support is enabled, the view
|
|
saves the language choice in the user's session. Otherwise, it saves the
|
|
language choice in a cookie that is by default named ``django_language``.
|
|
(The name can be changed through the ``LANGUAGE_COOKIE_NAME`` setting.)
|
|
|
|
After setting the language choice, Django redirects the user, following this
|
|
algorithm:
|
|
|
|
* Django looks for a ``next`` parameter in the ``POST`` data.
|
|
* If that doesn't exist, or is empty, Django tries the URL in the
|
|
``Referrer`` 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:
|
|
|
|
.. code-block:: html+django
|
|
|
|
<form action="/i18n/setlang/" method="post">
|
|
{% csrf_token %}
|
|
<input name="next" type="hidden" value="/next/page/" />
|
|
<select name="language">
|
|
{% for lang in LANGUAGES %}
|
|
<option value="{{ lang.0 }}">{{ lang.1 }}</option>
|
|
{% endfor %}
|
|
</select>
|
|
<input type="submit" value="Go" />
|
|
</form>
|