Source

django / docs / topics / i18n.txt

  1
  2
  3
  4
  5
  6
  7
  8
  9
 10
 11
 12
 13
 14
 15
 16
 17
 18
 19
 20
 21
 22
 23
 24
 25
 26
 27
 28
 29
 30
 31
 32
 33
 34
 35
 36
 37
 38
 39
 40
 41
 42
 43
 44
 45
 46
 47
 48
 49
 50
 51
 52
 53
 54
 55
 56
 57
 58
 59
 60
 61
 62
 63
 64
 65
 66
 67
 68
 69
 70
 71
 72
 73
 74
 75
 76
 77
 78
 79
 80
 81
 82
 83
 84
 85
 86
 87
 88
 89
 90
 91
 92
 93
 94
 95
 96
 97
 98
 99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
570
571
572
573
574
575
576
577
578
579
580
581
582
583
584
585
586
587
588
589
590
591
592
593
594
595
596
597
598
599
600
601
602
603
604
605
606
607
608
609
610
611
612
613
614
615
616
617
618
619
620
621
622
623
624
625
626
627
628
629
630
631
632
633
634
635
636
637
638
639
640
641
642
643
644
645
646
647
648
649
650
651
652
653
654
655
656
657
658
659
660
661
662
663
664
665
666
667
668
669
670
671
672
673
674
675
676
677
678
679
680
681
682
683
684
685
686
687
688
689
690
691
692
693
694
695
696
697
698
699
700
701
702
703
704
705
706
707
708
709
710
711
712
713
714
715
716
717
718
719
720
721
722
723
724
725
726
727
728
729
730
731
732
733
734
735
736
737
738
739
740
741
742
743
744
745
746
747
748
749
750
751
752
753
754
755
756
757
758
759
760
761
762
763
764
765
766
767
768
769
770
771
772
773
774
775
776
777
778
779
780
781
782
783
784
785
786
787
788
789
790
791
792
793
794
795
796
797
798
799
800
801
802
803
804
805
806
807
808
809
810
811
812
813
814
815
816
817
818
819
820
821
822
823
824
825
826
827
828
829
830
831
832
833
834
835
836
837
838
839
840
841
842
843
844
845
846
847
848
849
850
851
852
853
854
855
856
857
858
859
860
861
862
863
864
865
866
867
868
869
870
871
872
873
874
875
876
877
878
879
880
881
882
883
884
885
886
887
888
889
890
891
892
893
894
895
896
897
898
899
900
901
902
903
904
905
906
907
908
909
910
911
912
913
914
915
916
917
918
919
920
921
922
923
924
925
926
927
928
929
930
931
932
933
934
935
936
937
938
939
940
941
942
943
944
945
946
947
948
949
950
951
952
953
954
955
956
957
958
959
960
961
962
963
964
965
966
967
968
969
970
971
972
973
.. _topics-i18n:

====================
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.

If you don't need internationalization in your app
==================================================

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.

If you do need internationalization: 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.

1. 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 ``ugettext()``. It's
convention to import this as a shorter alias, ``_``, to save typing.

.. note::
    Python's standard library ``gettext`` module installs ``_()`` into the
    global namespace, as an alias for ``gettext()``. In Django, we have chosen
    not to follow this practice, for a couple of reasons:

      1. For international character set (Unicode) support, ``ugettext()`` is
         more useful than ``gettext()``. Sometimes, you should be using
         ``ugettext_lazy()`` as the default translation method for a particular
         file. Without ``_()`` in the global namespace, the developer has to
         think about which is the most appropriate translation function.

      2. The underscore character (``_``) is used to represent "the previous
         result" in Python's interactive shell and doctest tests. Installing a
         global ``_()`` function causes interference. Explicitly importing
         ``ugettext()`` as ``_()`` avoids this problem.

.. highlightlang:: python

In this example, the text ``"Welcome to my site."`` is marked as a translation
string::

    from django.utils.translation import ugettext as _

    def my_view(request):
        output = _("Welcome to my site.")
        return HttpResponse(output)

Obviously, you could code this without using the alias. This example is
identical to the previous one::

    from django.utils.translation import ugettext

    def my_view(request):
        output = ugettext("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,
``django-admin.py makemessages``, won't be able to find these strings. More on
``makemessages`` later.)

The strings you pass to ``_()`` or ``ugettext()`` can take placeholders,
specified with Python's standard named-string interpolation syntax. Example::

    def my_view(request, m, d):
        output = _('Today is %(month)s, %s(day)s.') % {'month': m, 'day': d}
        return HttpResponse(output)

This technique lets language-specific translations reorder the placeholder
text. For example, an English translation may be ``"Today is November, 26."``,
while a Spanish translation may be ``"Hoy es 26 de Noviembre."`` -- with the
placeholders (the month and the day) with their positions swapped.

For this reason, you should use named-string interpolation (e.g., ``%(day)s``)
instead of positional interpolation (e.g., ``%s`` or ``%d``) whenever you
have more than a single parameter. 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.ugettext_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-translations:

Lazy translation
~~~~~~~~~~~~~~~~

Use the function ``django.utils.translation.ugettext_lazy()`` to translate
strings lazily -- when the value is accessed rather than when the
``ugettext_lazy()`` function is called.

For example, to translate a model's ``help_text``, do the following::

    from django.utils.translation import ugettext_lazy

    class MyThing(models.Model):
        name = models.CharField(help_text=ugettext_lazy('This is the help text'))

In this example, ``ugettext_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 ``ugettext_lazy``, you can just alias it as
``_`` (underscore), like so::

    from django.utils.translation import ugettext_lazy as _

    class MyThing(models.Model):
        name = models.CharField(help_text=_('This is the help text'))

Always use lazy translations in :ref:`Django models <topics-db-models>`. 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 ugettext_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')

Pluralization
~~~~~~~~~~~~~

Use the function ``django.utils.translation.ungettext()`` to specify pluralized
messages. Example::

    from django.utils.translation import ungettext
    def hello_world(request, count):
        page = ungettext('there is %(count)d object', 'there are %(count)d objects', count) % {
            'count': count,
        }
        return HttpResponse(page)

``ungettext`` 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
----------------

.. highlightlang:: html+django

Translations in :ref:`Django templates <topics-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 either a constant string
(enclosed in single or double quotes) or variable content::

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

If the ``noop`` option is present, variable lookup still takes place but the
translation is skipped. This is useful when "stubbing out" content that will
require translation in the future::

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

It's not possible to mix a template variable inside a string within ``{% trans
%}``. If your translations require strings with variables (placeholders), use
``{% blocktrans %}``::

    {% blocktrans %}This string 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|length as counter %}
    There is only one {{ name }} object.
    {% plural %}
    There are {{ counter }} {{ name }} objects.
    {% endblocktrans %}

Internally, all block and inline translations use the appropriate
``ugettext`` / ``ungettext`` call.

Each ``RequestContext`` has access to three 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 (translated into the
      currently active locale).

    * ``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 locale'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::

    {% 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.

.. note::
    In this example, the translation infrastructure will be passed the string
    ``"yes,no"``, not the individual strings ``"yes"`` and ``"no"``. The
    translated string will need to contain the comma so that the filter
    parsing code knows how to split up the arguments. For example, a German
    translator might translate the string ``"yes,no"`` as ``"ja,nein"``
    (keeping the comma intact).

.. _Django templates: ../templates_python/

Working with lazy translation objects
-------------------------------------

.. highlightlang:: python

Using ``ugettext_lazy()`` and ``ungettext_lazy()`` to mark strings in models
and utility functions is a common operation. When you're working with these
objects elsewhere in your code, you should ensure that you don't accidentally
convert them to strings, because they should be converted as late as possible
(so that the correct locale is in effect). This necessitates the use of a
couple of helper functions.

Joining strings: string_concat()
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Standard Python string joins (``''.join([...])``) will not work on lists
containing lazy translation objects. Instead, you can use
``django.utils.translation.string_concat()``, which creates a lazy object that
concatenates its contents *and* converts them to strings only when the result
is included in a string. For example::

    from django.utils.translation import string_concat
    ...
    name = ugettext_lazy(u'John Lennon')
    instrument = ugettext_lazy(u'guitar')
    result = string_concat([name, ': ', instrument])

In this case, the lazy translations in ``result`` will only be converted to
strings when ``result`` itself is used in a string (usually at template
rendering time).

The allow_lazy() decorator
~~~~~~~~~~~~~~~~~~~~~~~~~~

Django offers many utility functions (particularly in ``django.utils``) that
take a string as their first argument and do something to that string. These
functions are used by template filters as well as directly in other code.

If you write your own similar functions and deal with translations, you'll
face the problem of what to do when the first argument is a lazy translation
object. You don't want to convert it to a string immediately, because you might
be using this function outside of a view (and hence the current thread's locale
setting will not be correct).

For cases like this, use the ``django.utils.functional.allow_lazy()``
decorator. It modifies the function so that *if* it's called with a lazy
translation as the first argument, the function evaluation is delayed until it
needs to be converted to a string.

For example::

    from django.utils.functional import allow_lazy

    def fancy_utility_function(s, ...):
        # Do some conversion on string 's'
        ...
    fancy_utility_function = allow_lazy(fancy_utility_function, unicode)

The ``allow_lazy()`` decorator takes, in addition to the function to decorate,
a number of extra arguments (``*args``) specifying the type(s) that the
original function can return. Usually, it's enough to include ``unicode`` here
and ensure that your function returns only Unicode strings.

Using this decorator means you can write your function and assume that the
input is a proper string, then add support for lazy translation objects at the
end.

.. _how-to-create-language-files:

2. 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. See the relevant :ref:LocaleMiddleware note`<locale-middleware-notes>`
    for more details.

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, ``django-admin.py makemessages``, that automates the
creation and upkeep of these files.

.. admonition:: A note to Django veterans

    The old tool ``bin/make-messages.py`` has been moved to the command
    ``django-admin.py makemessages`` to provide consistency throughout Django.

To create or update a message file, run this command::

    django-admin.py makemessages -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 Portuguese and ``de_AT`` for Austrian German.

The script should be run from one of three places:

    * The root directory of your Django project.
    * The root directory of your Django app.
    * The root ``django`` directory (not a Subversion checkout, but the one
      that is linked-to via ``$PYTHONPATH`` or is located somewhere on that
      path). This is only relevant when you are creating a translation for
      Django itself, see :ref:`contributing-translations`.

Th script runs over your project source tree or your application source tree and
pulls out all strings marked for translation. It creates (or updates) a message
file in the directory ``locale/LANG/LC_MESSAGES``. In the ``de`` example, the
file will be ``locale/de/LC_MESSAGES/django.po``.

By default ``django-admin.py makemessages`` examines every file that has the
``.html`` file extension. In case you want to override that default, use the
``--extension`` or ``-e`` option to specify the file extensions to examine::

    django-admin.py makemessages -l de -e txt

Separate multiple extensions with commas and/or use ``-e`` or ``--extension``
multiple times::

    django-admin.py makemessages -l=de -e=html,txt -e xml

When `creating JavaScript translation catalogs`_ you need to use the special
'djangojs' domain, **not** ``-e js``.

.. _create a JavaScript translation catalog: `Creating JavaScript translation catalogs`_

.. admonition:: No gettext?

    If you don't have the ``gettext`` utilities installed, ``django-admin.py
    makemessages`` will create empty files. If that's the case, either install
    the ``gettext`` utilities or just copy the English message file
    (``locale/en/LC_MESSAGES/django.po``) if available and use it as a starting
    point; it's just an empty translation file.

.. admonition:: Working on Windows?

   If you're using Windows and need to install the GNU gettext utilities so
   ``django-admin makemessages`` works see `gettext on Windows`_ for more
   information.

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 ``django-admin.py makemessages`` 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, in the form of a comment line
      prefixed with ``#`` and locted above the ``msgid`` line, 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. Due to the way the ``gettext`` tools
    work internally and because we want to allow non-ASCII source strings in
    Django's core and your applications, you **must** use UTF-8 as the encoding
    for your PO file. This means that everybody will be using the same
    encoding, which is important when Django processes the PO files.

To reexamine all source code and templates for new translation strings and
update all message files for **all** languages, run this::

    django-admin.py makemessages -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 ``django-admin.py compilemessages`` 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 ``django-admin.py makemessages``, run ``django-admin.py
compilemessages`` like this::

   django-admin.py compilemessages

That's it. Your translations are ready for use.

.. admonition:: A note to Django veterans

    The old tool ``bin/compile-messages.py`` has been moved to the command
    ``django-admin.py compilemessages`` to provide consistency throughout
    Django.

.. admonition:: Working on Windows?

   If you're using Windows and need to install the GNU gettext utilities so
   ``django-admin compilemessages`` works see `gettext on Windows`_ for more
   information.

3. 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 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 :ref:`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.
    
      .. versionchanged:: 1.0
    
      In Django version 0.96 and before, the cookie's name is hard-coded to
      ``django_language``. In Django 1,0, The cookie name 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 language format, 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).

      .. _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" ``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 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 validation
      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
: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

.. _translations-in-your-own-projects:

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 Django-provided 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
    :ref:`settings-without-django-settings-module`, 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.)

All message file repositories are structured the same way. They are:

    * ``$APPPATH/locale/<language>/LC_MESSAGES/django.(po|mo)``
    * ``$PROJECTPATH/locale/<language>/LC_MESSAGES/django.(po|mo)``
    * All paths listed in ``LOCALE_PATHS`` in your settings file are
      searched in that order for ``<language>/LC_MESSAGES/django.(po|mo)``
    * ``$PYTHONPATH/django/conf/locale/<language>/LC_MESSAGES/django.(po|mo)``

To create message files, you use the same ``django-admin.py makemessages``
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 ``django-admin.py compilemessages``
to produce the binary ``django.mo`` files that are used by ``gettext``.

You can also run ``django-admin.py compilemessages --settings=path.to.settings``
to make the compiler process all the directories in your ``LOCALE_PATHS``
setting.

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 ``makemessages``: ``makemessages`` 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,

``django-admin.py makemessages`` on the project level will only translate
strings that are connected to your explicit project and not strings that are
distributed independently.

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 if you're
using the Django development version.)

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">
    <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>

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<packages>\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::

    <script type="text/javascript" src="/path/to/jsi18n/"></script>

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 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).

Creating JavaScript translation catalogs
----------------------------------------

You create and update the translation catalogs the same way as the other

Django translation catalogs -- with the django-admin.py makemessages tool. The
only difference is you need to provide a ``-d djangojs`` parameter, like this::

    django-admin.py makemessages -d djangojs -l de

This would create or update the translation catalog for JavaScript for German.
After updating translation catalogs, just run ``django-admin.py compilemessages``
the same way as you do with normal Django translation catalogs.

Specialties of Django translation
==================================

If you know ``gettext``, you might note these specialties in the way Django
does translation:

    * The string domain is ``django`` or ``djangojs``. This 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 doesn't use ``xgettext`` alone. It uses Python wrappers around
      ``xgettext`` and ``msgfmt``. This is mostly for convenience.

``gettext`` on Windows
======================

This is only needed for people who either want to extract message IDs or compile
message files (``.po``). Translation work itself just involves editing existing
files of this type, but if you want to create your own message files, or want to
test or compile a changed message file, you will need the ``gettext`` utilities:

    * Download the following zip files from
      http://sourceforge.net/projects/gettext

      * ``gettext-runtime-X.bin.woe32.zip``
      * ``gettext-tools-X.bin.woe32.zip``
      * ``libiconv-X.bin.woe32.zip``

    * Extract the 3 files in the same folder (i.e. ``C:\Program
      Files\gettext-utils``)

    * Update the system PATH:

      * ``Control Panel > System > Advanced > Environment Variables``
      * In the ``System variables`` list, click ``Path``, click ``Edit``
      * Add ``;C:\Program Files\gettext-utils\bin`` at the end of the
        ``Variable value`` field