Chapter 20: Internationalizati-Mastering Django: Core

Django was originally developed right in the middle of the United States quite literally, as Lawrence, Kansas, is less than 40 miles from the geographic center of the continental United States. Like most open source projects, though, Djangos community grew to include people from all over the globe. As Djangos community became increasingly diverse, internationalization and localization became increasingly important.

Django itself is fully internationalized; all strings are marked for translation, and settings control the display of locale-dependent values like dates and times. Django also ships with more than 50 different localization files. If youre not a native English speaker, theres a good chance that Django is already translated into your primary language.

The same internationalization framework used for these localizations is available for you to use in your own code and templates.

Because many developers have at best a fuzzy understanding of what internationalization and localization actually mean, we will begin with a few definitions.

Internationalization: in JavaScript code
The `javascript_catalog` view
Using the JavaScript translation catalog
Note on performance

Internationalization: in URL patterns Language prefix in URL patterns Translating URL patterns Reversing in templates Localization: how to create language files Message files Compiling message files Creating message files from JavaScript source code `gettext` on Windows Customizing the `makemessages` command Miscellaneous The `set_language` redirect view Explicitly setting the active language Using translations outside views and templates Language cookie Implementation notes Specialties of Django translation How Django discovers language preference How Django discovers translations

Definitions

internationalization

Refers to the process of designing programs for the potential use of any locale. This process is usually done by software developers. Internationalization includes marking text (such as UI elements and error messages) for future translation, abstracting the display of dates and times so that different local standards may be observed, providing support for differing time zones, and generally making sure that the code contains no assumptions about the location of its users. Youll often see internationalization abbreviated I18N. (The 18 refers to the number of letters omitted between the initial I and the terminal N.)

localization

Refers to the process of actually translating an internationalized program for use in a particular locale. This work is usually done by translators. Youll sometimes see localization abbreviated as L10N.

More details can be found in the W3C Web Internationalization FAQ, the Wikipedia article or the GNU gettext documentation.

Here are some other terms that will help us to handle a common language:

locale name

A locale name, either a language specification of the form ll or a combined language and country specification of the form ll_CC. Examples: it, de_AT, es, pt_BR. The language part is always in lower case and the country part in upper case. The separator is an underscore.

language code

Represents the name of a language. Browsers send the names of the languages they accept in the Accept-Language HTTP header using this format. Examples: it, de-at, es, pt-br. Language codes are generally represented in lower-case, but the HTTP Accept-Language header is case-insensitive. The separator is a dash.

message file

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.

translation string

A literal that can be translated.

format file

A format file is a Python module that defines the data formats for a given locale.

Translation

In order to make a Django project translatable, you have to add a minimal number 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 users language, if a translation for this text is available in that language. Its your responsibility to mark translatable strings; the system can only translate strings it knows about.

Django then provides utilities to extract the translation strings into a message file. This file is a convenient way for translators to provide the equivalent of the translation strings in the target language. Once the translators have filled in the message file, it must be compiled. This process relies on the GNU gettext toolset.

Once this is done, Django takes care of translating Web apps on the fly in each available language, according to users language preferences.

Essentially, Django does two things:

It lets developers and template authors specify which parts of their applications should be translatable.
It uses that information to translate Web applications for particular users according to their language preferences.

Djangos internationalization hooks are on by default, and that means theres a bit of i18n-related overhead in certain places of the framework. If you dont use internationalization, you should take the two seconds to set USE_I18N = False <USE_I18N> in your settings file. Then Django will make some optimizations so as not to load the internationalization machinery.

Note

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

Note

Make sure youve activated translation for your project (the fastest way is to check if MIDDLEWARE_CLASSESincludes django.middleware.locale.LocaleMiddleware). If you havent yet, see how-django-discovers-language-preference.

If You Dont Need Internationalization:

Djangos internationalization hooks are enabled by default, which incurs a small bit of overhead. If you dont use internationalization, you should set USE_I18N = False in your settings file. If USE_I18N is set toFalse, then Django will make some optimizations so as not to load the internationalization machinery.

Internationalization: in Python code

Standard translation

Specify a translation string by using the function ugettext(). Its convention to import this as a shorter alias, _, to save typing.

Note

Pythons 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:

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

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

from django.utils.translation import ugettext as _
from django.http import HttpResponse

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
from django.http import HttpResponse

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, heres 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 Djangos translation-string-detecting utility, django-admin makemessages , wont be able to find these strings. More on makemessages later.)

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

def my_view(request, m, d):
    output = _("Today is %(month)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 month and the day placeholders 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 wouldnt be able to reorder placeholder text.

Comments for translators

If you would like to give translators hints about a translatable string, you can add a comment prefixed with the Translators keyword on the line preceding the string, e.g.:

def my_view(request):
    # Translators: This message appears on the home page only
    output = ugettext("Welcome to my site.")

The comment will then appear in the resulting .po file associated with the translatable construct located below it and should also be displayed by most translation tools.

Note

Just for completeness, this is the corresponding fragment of the resulting .po file:

#. Translators: This message appears on the home page only
# path/to/python/file.py:123
msgid "Welcome to my site."
msgstr ""

This also works in templates. See translator-comments-in-templates for more details.

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.

Pluralization

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

ungettext takes three arguments: the singular translation string, the plural translation string and the number of objects.

This function is useful when you need your Django application to be localizable to languages where the number and complexity of plural forms is greater than the two forms used in English (object for the singular and objects for all the cases where count is different from one, irrespective of its value.)

For example:

from django.utils.translation import ungettext
from django.http import HttpResponse

def hello_world(request, count):
    page = ungettext(
        "there is %(count)d object",
        "there are %(count)d objects",
    count) % {
        "count": count,
    }
    return HttpResponse(page)

In this example the number of objects is passed to the translation languages as the count variable.

Note that pluralization is complicated and works differently in each language. Comparing count to 1 isnt always the correct rule. This code looks sophisticated, but will produce incorrect results for some languages:

from django.utils.translation import ungettext
from myapp.models import Report

count = Report.objects.count()
if count == 1:
    name = Report._meta.verbose_name
else:
    name = Report._meta.verbose_name_plural

text = ungettext(
    "There is %(count)d %(name)s available.",
    "There are %(count)d %(name)s available.",
    count
) % {
    "count": count,
    "name": name
}

Dont try to implement your own singular-or-plural logic, it wont be correct. In a case like this, consider something like the following:

text = ungettext(
    "There is %(count)d %(name)s object available.",
    "There are %(count)d %(name)s objects available.",
    count
) % {
    "count": count,
    "name": Report._meta.verbose_name,
}

Note

When using ungettext(), make sure you use a single name for every extrapolated variable included in the literal. In the examples above, note how we used the name Python variable in both translation strings. This example, besides being incorrect in some languages as noted above, would fail:

text = ungettext(
    "There is %(count)d %(name)s available.",
    "There are %(count)d %(plural_name)s available.",
    count
) % {
    "count": Report.objects.count(),
    "name": Report._meta.verbose_name,
    "plural_name": Report._meta.verbose_name_plural
}

You would get an error when running django-admin compilemessages:

a format specification for argument "name", as in "msgstr[0]", doesn"t exist in "msgid"

Contextual markers

Sometimes words have several meanings, such as "May" in English, which refers to a month name and to a verb. To enable translators to translate these words correctly in different contexts, you can use thedjango.utils.translation.pgettext() function, or the django.utils.translation.npgettext() function if the string needs pluralization. Both take a context string as the first variable.

In the resulting .po file, the string will then appear as often as there are different contextual markers for the same string (the context will appear on the msgctxt line), allowing the translator to give a different translation for each of them.

For example:

from django.utils.translation import pgettext

month = pgettext("month name", "May")

or:

from django.db import models
from django.utils.translation import pgettext_lazy

class MyThing(models.Model):
    name = models.CharField(help_text=pgettext_lazy(
        "help text for MyThing model", "This is the help text"))

will appear in the .po file as:

msgctxt "month name"
msgid "May"
msgstr ""

Contextual markers are also supported by the trans and blocktrans template tags.

Lazy translation

Use the lazy versions of translation functions in django.utils.translation (easily recognizable by the lazysuffix in their names) to translate strings lazily when the value is accessed rather than when theyre called.

These functions store 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 in template rendering.

This is essential when calls to these functions are located in code paths that are executed at module load time.

This is something that can easily happen when defining models, forms and model forms, because Django implements these such that their fields are actually class-level attributes. For that reason, make sure to use lazy translations in the following cases:

MODEL FIELDS AND RELATIONSHIPS `VERBOSE_NAME` AND `HELP_TEXT` OPTION VALUES

For example, to translate the help text of the name field in the following model, do the following:

from django.db import models
from django.utils.translation import ugettext_lazy as _

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

You can mark names of ForeignKey, ManyToManyField or OneToOneField relationship as translatable by using their verbose_name options:

class MyThing(models.Model):
    kind = models.ForeignKey(ThingKind, related_name="kinds",
                             verbose_name=_("kind"))

Just like you would do in verbose_name you should provide a lowercase verbose name text for the relation as Django will automatically titlecase it when required.

MODEL VERBOSE NAMES VALUES

It is recommended to always provide explicit verbose_name and verbose_name_plural options rather than relying on the fallback English-centric and somewhat naïve determination of verbose names Django performs by looking at the models class name:

from django.db import models
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 = _("my things")

MODEL METHODS `SHORT_DESCRIPTION` ATTRIBUTE VALUES

For model methods, you can provide translations to Django and the admin site with the short_descriptionattribute:

from django.db import models
from django.utils.translation import ugettext_lazy as _

class MyThing(models.Model):
    kind = models.ForeignKey(ThingKind, related_name="kinds",
                             verbose_name=_("kind"))

    def is_mouse(self):
        return self.kind.type == MOUSE_TYPE
    is_mouse.short_description = _("Is it a mouse?")

Working with lazy translation objects

The result of a ugettext_lazy() call can be used wherever you would use a unicode string (an object with type unicode) in Python. If you try to use it where a bytestring (a str object) is expected, things will not work as expected, since a ugettext_lazy() object doesnt know how to convert itself to a bytestring. You cant use a unicode string inside a bytestring, either, so this is consistent with normal Python behavior. For example:

# This is fine: putting a unicode proxy into a unicode string.
"Hello %s" % ugettext_lazy("people")

# This will not work, since you cannot insert a unicode object
# into a bytestring (nor can you insert our unicode proxy there)
b"Hello %s" % ugettext_lazy("people")

If you ever see output that looks like "hello <django.utils.functional...>", you have tried to insert the result of ugettext_lazy() into a bytestring. Thats a bug in your code.

If you dont like the long ugettext_lazy name, you can just alias it as _ (underscore), like so:

from django.db import models
from django.utils.translation import ugettext_lazy as _

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

Using ugettext_lazy() and ungettext_lazy() to mark strings in models and utility functions is a common operation. When youre working with these objects elsewhere in your code, you should ensure that you dont 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 the helper function described next.

LAZY TRANSLATIONS AND PLURAL

When using lazy translation for a plural string ([u]n[p]gettext_lazy), you generally dont know the numberargument at the time of the string definition. Therefore, you are authorized to pass a key name instead of an integer as the number argument. Then number will be looked up in the dictionary under that key during string interpolation. Heres example:

from django import forms
from django.utils.translation import ugettext_lazy

class MyForm(forms.Form):
    error_message = ungettext_lazy("You only provided %(num)d argument",
        "You only provided %(num)d arguments", "num")

    def clean(self):
        # ...
        if error:
            raise forms.ValidationError(self.error_message % {"num": number})

If the string contains exactly one unnamed placeholder, you can interpolate directly with the numberargument:

class MyForm(forms.Form):
    error_message = ungettext_lazy("You provided %d argument",
        "You provided %d arguments")

    def clean(self):
        # ...
        if error:
            raise forms.ValidationError(self.error_message % number)

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
from django.utils.translation import ugettext_lazy
...
name = ugettext_lazy("John Lennon")
instrument = ugettext_lazy("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).

OTHER USES OF LAZY IN DELAYED TRANSLATIONS

For any other case where you would like to delay the translation, but have to pass the translatable string as argument to another function, you can wrap this function inside a lazy call yourself. For example:

from django.utils import six  # Python 3 compatibility
from django.utils.functional import lazy
from django.utils.safestring import mark_safe
from django.utils.translation import ugettext_lazy as _

mark_safe_lazy = lazy(mark_safe, six.text_type)

And then later:

lazy_string = mark_safe_lazy(_("<p>My <strong>string!</strong></p>"))

Localized names of languages

get_language_info()

The get_language_info() function provides detailed information about languages:

>>> from django.utils.translation import get_language_info
>>> li = get_language_info("de")
>>> print(li["name"], li["name_local"], li["bidi"])
German Deutsch False

The name and name_local attributes of the dictionary contain the name of the language in English and in the language itself, respectively. The bidi attribute is True only for bi-directional languages.

The source of the language information is the django.conf.locale module. Similar access to this information is available for template code. See below.

Internationalization: in template code

Translations in Django templates uses two template tags and a slightly different syntax than in Python code. To give your template access to these tags, put {% load i18n %} toward the top of your template. As with all template tags, this tag needs to be loaded in all templates which use translations, even those templates that extend from other templates which have already loaded the i18n tag.

`trans` template tag

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>

Internally, inline translations use an ugettext() call.

In case a template var (myvar above) is passed to the tag, the tag will first resolve such variable to a string at run-time and then look up that string in the message catalogs.

Its not possible to mix a template variable inside a string within {% trans %}. If your translations require strings with variables (placeholders), use {% blocktrans %}<blocktrans> instead.

If youd like to retrieve a translated string without displaying it, you can use the following syntax:

{% trans "This is the title" as the_title %}

<title>{{ the_title }}</title>
<meta name="description" content="{{ the_title }}">

In practice youll use this to get strings that are used in multiple places or should be used as arguments for other template tags or filters:

{% trans "starting point" as start %}
{% trans "end point" as end %}
{% trans "La Grande Boucle" as race %}

<h1>
  <a href="/" title="{% blocktrans %}Back to "{{ race }}" homepage{% endblocktrans %}">{{ race }}</a>
</h1>
<p>
{% for stage in tour_stages %}
    {% cycle start end %}: {{ stage }}{% if forloop.counter|divisibleby:2 %}<br />{% else %}, {% endif %}
{% endfor %}
</p>

{% trans %} also supports contextual markers using the context keyword:

{% trans "May" context "month name" %}

`blocktrans` template tag

Contrarily to the trans tag, the blocktrans tag allows you to mark complex sentences consisting of literals and variable content for translation by making use of placeholders:

{% blocktrans %}This string will have {{ value }} inside.{% endblocktrans %}

To translate a template expression say, accessing object attributes or using template filters you need to bind the expression to a local variable for use within the translation block. Examples:

{% blocktrans with amount=article.price %}
That will cost $ {{ amount }}.
{% endblocktrans %}

{% blocktrans with myvar=value|filter %}
This will have {{ myvar }} inside.
{% endblocktrans %}

You can use multiple expressions inside a single blocktrans tag:

{% blocktrans with book_t=book|title author_t=author|title %}
This is {{ book_t }} by {{ author_t }}
{% endblocktrans %}

Note

The previous more verbose format is still supported: {% blocktrans with book|title as book_t andauthor|title as author_t %}

Other block tags (for example {% for %} or {% if %}) are not allowed inside a blocktrans tag.

If resolving one of the block arguments fails, blocktrans will fall back to the default language by deactivating the currently active language temporarily with the deactivate_all() function.

This tag also provides for pluralization. To use it:

Designate and bind a counter value with the name count. This value will be the one used to select the right plural form.
Specify both the singular and plural forms separating them with the {% plural %} tag within the {%blocktrans %} and {% endblocktrans %} tags.

An example:

{% blocktrans count counter=list|length %}
There is only one {{ name }} object.
{% plural %}
There are {{ counter }} {{ name }} objects.
{% endblocktrans %}

A more complex example:

{% blocktrans with amount=article.price count years=i.length %}
That will cost $ {{ amount }} per year.
{% plural %}
That will cost $ {{ amount }} per {{ years }} years.
{% endblocktrans %}

When you use both the pluralization feature and bind values to local variables in addition to the counter value, keep in mind that the blocktrans construct is internally converted to an ungettext call. This means the same notes regarding ungettext variables apply.

Reverse URL lookups cannot be carried out within the blocktrans and should be retrieved (and stored) beforehand:

{% url "path.to.view" arg arg2 as the_url %}
{% blocktrans %}
This is a URL: {{ the_url }}
{% endblocktrans %}

{% blocktrans %} also supports contextual

using the context keyword:

{% blocktrans with name=user.username context "greeting" %}Hi {{ name }}{% endblocktrans %}

Another feature {% blocktrans %} supports is the trimmed option. This option will remove newline characters from the beginning and the end of the content of the {% blocktrans %} tag, replace any whitespace at the beginning and end of a line and merge all lines into one using a space character to separate them. This is quite useful for indenting the content of a {% blocktrans %} tag without having the indentation characters end up in the corresponding entry in the PO file, which makes the translation process easier.

For instance, the following {% blocktrans %} tag:

{% blocktrans trimmed %}
  First sentence.
  Second paragraph.
{% endblocktrans %}

will result in the entry "First sentence. Second paragraph." in the PO file, compared to " First sentence. Second sentence. ", if the trimmed option had not been specified.

String literals passed to tags and filters

You can translate string literals passed as arguments to tags and filters by using the familiar _() syntax:

{% some_tag _("Page not found") value|yesno:_("yes,no") %}

In this case, both the tag and the filter will see the translated string, so they dont 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).

Comments for translators in templates

Just like with Python code , these notes for translators can be specified using comments, either with thecomment tag:

{% comment %}Translators: View verb{% endcomment %}
{% trans "View" %}

{% comment %}Translators: Short intro blurb{% endcomment %}
<p>{% blocktrans %}A multiline translatable
literal.{% endblocktrans %}</p>

or with the {# … #} one-line comment constructs :

{# Translators: Label of a button that triggers search #}
<button type="submit">{% trans "Go" %}</button>

{# Translators: This is a text of the base template #}
{% blocktrans %}Ambiguous translatable block of text{% endblocktrans %}

Note

Just for completeness, these are the corresponding fragments of the resulting .po file:

#. Translators: View verb
# path/to/template/file.html:10
msgid "View"
msgstr ""

#. Translators: Short intro blurb
# path/to/template/file.html:13
msgid ""
"A multiline translatable"
"literal."
msgstr ""

# ...

#. Translators: Label of a button that triggers search
# path/to/template/file.html:100
msgid "Go"
msgstr ""

#. Translators: This is a text of the base template
# path/to/template/file.html:103
msgid "Ambiguous translatable block of text"
msgstr ""

Switching language in templates

If you want to select a language within a template, you can use the language template tag:

{% load i18n %}

{% get_current_language as LANGUAGE_CODE %}
<!-- Current language: {{ LANGUAGE_CODE }} -->
<p>{% trans "Welcome to our page" %}</p>

{% language "en" %}
    {% get_current_language as LANGUAGE_CODE %}
    <!-- Current language: {{ LANGUAGE_CODE }} -->
    <p>{% trans "Welcome to our page" %}</p>
{% endlanguage %}

While the first occurrence of Welcome to our page uses the current language, the second will always be in English.

Other tags

These tags also require a {% load i18n %}.

{% get_available_languages as LANGUAGES %} returns a list of tuples in which the first element is thelanguage code and the second is the language name (translated into the currently active locale).
{% get_current_language as LANGUAGE_CODE %} returns the current users preferred language, as a string. Example: en-us. (See how-django-discovers-language-preference.)
{% get_current_language_bidi as LANGUAGE_BIDI %} returns the current locales direction. If True, its a right-to-left language, e.g.: Hebrew, Arabic. If False its a left-to-right language, e.g.: English, French, German etc.

If you enable the django.template.context_processors.i18n context processor then each RequestContext will have access to LANGUAGES, LANGUAGE_CODE, and LANGUAGE_BIDI as defined above.

The i18n context processor is not enabled by default for new projects.

You can also retrieve information about any of the available languages using provided template tags and filters. To get information about a single language, use the {% get_language_info %} tag:

{% get_language_info for LANGUAGE_CODE as lang %}
{% get_language_info for "pl" as lang %}

You can then access the information:

Language code: {{ lang.code }}<br />
Name of language: {{ lang.name_local }}<br />
Name in English: {{ lang.name }}<br />
Bi-directional: {{ lang.bidi }}

You can also use the {% get_language_info_list %} template tag to retrieve information for a list of languages (e.g. active languages as specified in LANGUAGES). See the section about the set_language redirect view for an example of how to display a language selector using {% get_language_info_list %}.

In addition to LANGUAGES style list of tuples, {% get_language_info_list %} supports simple lists of language codes. If you do this in your view:

context = {"available_languages": ["en", "es", "fr"]}
return render(request, "mytemplate.html", context)

you can iterate over those languages in the template:

{% get_language_info_list for available_languages as langs %}
{% for lang in langs %} ... {% endfor %}

There are also simple filters available for convenience:

{{ LANGUAGE_CODE|language_name }} (German)
{{ LANGUAGE_CODE|language_name_local }} (Deutsch)
{{ LANGUAGE_CODE|language_bidi }} (False)

Internationalization: in JavaScript code

Adding translations to JavaScript poses some problems:

JavaScript code doesnt have access to a gettext implementation.
JavaScript code doesnt 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

django.views.i18n.javascript_catalog(request, domain=’djangojs’, packages=None)

The main solution to these problems is the django.views.i18n.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 applications or Django core, according to what you specify in either the info_dict or the URL. Paths listed in LOCALE_PATHS are also included.

You hook it up like this:

from django.views.i18n import javascript_catalog

js_info_dict = {
    "packages": ("your.app.package",),
}

urlpatterns = [
    url(r"^jsi18n/$", javascript_catalog, js_info_dict),
]

Each string in packages should be in Python dotted-package syntax (the same format as the strings inINSTALLED_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.

The precedence of translations is such that the packages appearing later in the packages argument have higher precedence than the ones appearing at the beginning, this is important in the case of clashing translations for the same literal.

By default, the view uses the djangojs gettext domain. This can be changed by altering the domainargument.

You can make the view dynamic by putting the packages into the URL pattern:

urlpatterns = [
    url(r"^jsi18n/(?P<packages>S+?)/$", 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 dont 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.

The JavaScript translations found in the paths listed in the LOCALE_PATHS setting are also always included. To keep consistency with the translations lookup order algorithm used for Python and templates, the directories listed in LOCALE_PATHS have the highest precedence with the ones appearing first having higher precedence than the ones appearing later.

Using the JavaScript translation catalog

To use the catalog, just pull in the dynamically generated script like this:

<script type="text/javascript" src="{% url "django.views.i18n.javascript_catalog" %}"></script>

This uses reverse URL lookup to find the URL of the JavaScript catalog view. 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. objcontains 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 shouldnt go over the top with string interpolation, though: this is still JavaScript, so the code has to make repeated regular-expression substitutions. This isnt 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).

Note on performance

The javascript_catalog() view generates the catalog from .mo files on every request. Since its output is constant at least for a given version of a site its a good candidate for caching.

Server-side caching will reduce CPU load. Its easily implemented with the cache_page() decorator. To trigger cache invalidation when your translations change, provide a version-dependent key prefix, as shown in the example below, or map the view at a version-dependent URL.

from django.views.decorators.cache import cache_page
from django.views.i18n import javascript_catalog

# The value returned by get_version() must change when translations change.
@cache_page(86400, key_prefix="js18n-%s" % get_version())
def cached_javascript_catalog(request, domain="djangojs", packages=None):
    return javascript_catalog(request, domain, packages)

Client-side caching will save bandwidth and make your site load faster. If youre using ETags (USE_ETAGS =True <USE_ETAGS>), youre already covered. Otherwise, you can apply conditional decorators . In the following example, the cache is invalidated whenever you restart your application server.

from django.utils import timezone
from django.views.decorators.http import last_modified
from django.views.i18n import javascript_catalog

last_modified_date = timezone.now()

@last_modified(lambda req, **kw: last_modified_date)
def cached_javascript_catalog(request, domain="djangojs", packages=None):
    return javascript_catalog(request, domain, packages)

You can even pre-generate the javascript catalog as part of your deployment procedure and serve it as a static file. This radical technique is implemented in django-statici18n.

Internationalization: in URL patterns

Django provides two mechanisms to internationalize URL patterns:

Adding the language prefix to the root of the URL patterns to make it possible for LocaleMiddleware to detect the language to activate from the requested URL.
Making URL patterns themselves translatable via the django.utils.translation.ugettext_lazy() function.

Warning

Using either one of these features requires that an active language be set for each request; in other words, you need to have django.middleware.locale.LocaleMiddleware in your MIDDLEWARE_CLASSES setting.

Language prefix in URL patterns

django.conf.urls.i18n.i18n_patterns(prefix, pattern_description, …)

Deprecated since version 1.8: The prefix argument to i18n_patterns() has been deprecated and will not be supported in Django 2.0. Simply pass a list of django.conf.urls.url() instances instead.

This function can be used in your root URLconf and Django will automatically prepend the current active language code to all url patterns defined within i18n_patterns(). Example URL patterns:

from django.conf.urls import include, url
from django.conf.urls.i18n import i18n_patterns

from about import views as about_views
from news import views as news_views
from sitemap.views import sitemap

urlpatterns = [
    url(r"^sitemap.xml$", sitemap, name="sitemap_xml"),
]

news_patterns = [
    url(r"^$", news_views.index, name="index"),
    url(r"^category/(?P<slug>[w-]+)/$", news_views.category, name="category"),
    url(r"^(?P<slug>[w-]+)/$", news_views.details, name="detail"),
]

urlpatterns += i18n_patterns(
    url(r"^about/$", about_views.main, name="about"),
    url(r"^news/", include(news_patterns, namespace="news")),
)

After defining these URL patterns, Django will automatically add the language prefix to the URL patterns that were added by the i18n_patterns function. Example:

from django.core.urlresolvers import reverse
from django.utils.translation import activate

>>> activate("en")
>>> reverse("sitemap_xml")
"/sitemap.xml"
>>> reverse("news:index")
"/en/news/"

>>> activate("nl")
>>> reverse("news:detail", kwargs={"slug": "news-slug"})
"/nl/news/news-slug/"

Warning

i18n_patterns() is only allowed in your root URLconf. Using it within an included URLconf will throw anImproperlyConfigured exception.

Warning

Ensure that you dont have non-prefixed URL patterns that might collide with an automatically-added language prefix.

Translating URL patterns

URL patterns can also be marked translatable using the ugettext_lazy() function. Example:

from django.conf.urls import include, url
from django.conf.urls.i18n import i18n_patterns
from django.utils.translation import ugettext_lazy as _

from about import views as about_views
from news import views as news_views
from sitemaps.views import sitemap

urlpatterns = [
    url(r"^sitemap.xml$", sitemap, name="sitemap_xml"),
]

news_patterns = [
    url(r"^$", news_views.index, name="index"),
    url(_(r"^category/(?P<slug>[w-]+)/$"), news_views.category, name="category"),
    url(r"^(?P<slug>[w-]+)/$", news_views.details, name="detail"),
]

urlpatterns += i18n_patterns(
    url(_(r"^about/$"), about_views.main, name="about"),
    url(_(r"^news/"), include(news_patterns, namespace="news")),
)

After youve created the translations, the reverse() function will return the URL in the active language. Example:

from django.core.urlresolvers import reverse
from django.utils.translation import activate

>>> activate("en")
>>> reverse("news:category", kwargs={"slug": "recent"})
"/en/news/category/recent/"

>>> activate("nl")
>>> reverse("news:category", kwargs={"slug": "recent"})
"/nl/nieuws/categorie/recent/"

Warning

In most cases, its best to use translated URLs only within a language-code-prefixed block of patterns (using i18n_patterns()), to avoid the possibility that a carelessly translated URL causes a collision with a non-translated URL pattern.

Reversing in templates

If localized URLs get reversed in templates they always use the current language. To link to a URL in another language use the language template tag. It enables the given language in the enclosed template section:

{% load i18n %}

{% get_available_languages as languages %}

{% trans "View this category in:" %}
{% for lang_code, lang_name in languages %}
    {% language lang_code %}
    <a href="{% url "category" slug=category.slug %}">{{ lang_name }}</a>
    {% endlanguage %}
{% endfor %}

The language tag expects the language code as the only argument.

Localization: how to create language files

Once the string literals of an application have been tagged for later translation, the translation themselves need to be written (or obtained). Heres how that works.

Message files

The first step is to create a message file for a new language. A message file is a plain-text file, representing a single language, that contains all available translation strings and how they should be represented in the given language. Message files have a .po file extension.

Django comes with a tool, django-admin makemessages , that automates the creation and upkeep of these files.

Gettext utilities

The makemessages command (and compilemessages discussed later) use commands from the GNU gettext toolset: xgettext, msgfmt, msgmerge and msguniq.

The minimum version of the gettext utilities supported is 0.15.

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

django-admin makemessages -l de

…where de is the locale name for the message file you want to create. For example, pt_BR for Brazilian Portuguese, de_AT for Austrian German or id for Indonesian.

The script should be run from one of two places:

The root directory of your Django project (the one that contains manage.py).
The root directory of one of your Django apps.

The script runs over your project source tree or your application source tree and pulls out all strings marked for translation (see how-django-discovers-translations and be sure LOCALE_PATHS is configured correctly). 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.

When you run makemessages from the root directory of your project, the extracted strings will be automatically distributed to the proper message files. That is, a string extracted from a file of an app containing a locale directory will go in a message file under that directory. A string extracted from a file of an app without any locale directory will either go in a message file under the directory listed first inLOCALE_PATHS or will generate an error if LOCALE_PATHS is empty.

By default django-admin makemessages examines every file that has the .html or .txt 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 makemessages -l de -e txt

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

django-admin makemessages -l de -e html,txt -e xml

Warning

When creating message files from JavaScript source code you need to use the special djangojs domain, not-e js.

No gettext?

If you dont have the gettext utilities installed, makemessages will create empty files. If thats 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; its just an empty translation file.

Working on Windows?

If youre using Windows and need to install the GNU gettext utilities so 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 maintainers 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 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. Dont change it.
msgstr is where you put the language-specific translation. It starts out empty, so its 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 located 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. Dont forget trailing spaces within the strings; otherwise, theyll be tacked together without whitespace!

Mind your charset

Due to the way the gettext tools work internally and because we want to allow non-ASCII source strings in Djangos core and your applications, you must use UTF-8 as the encoding for your PO files (the default when PO files are created). 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 alllanguages, run this:

django-admin makemessages -a

Compiling message files

After you create your message file and each time you make changes to it youll need to compile it into a more efficient form, for use by gettext. Do this with the django-admin compilemessages utility.

This tool runs over all available .po files and creates .mo files, which are binary files optimized for use bygettext. In the same directory from which you ran django-admin makemessages , run django-admin compilemessages like this:

django-admin compilemessages

Thats it. Your translations are ready for use.

Working on Windows?

If youre using Windows and need to install the GNU gettext utilities so django-admin compilemessages works see gettext_on_windows for more information.

.po files: Encoding and BOM usage.

Django only supports .po files encoded in UTF-8 and without any BOM (Byte Order Mark) so if your text editor adds such marks to the beginning of files by default then you will need to reconfigure it.

Creating message files from JavaScript source code

You create and update the message files the same way as the other Django message files with the django-admin makemessages tool. The only difference is you need to explicitly specify what in gettext parlance is known as a domain in this case the djangojs domain, by providing a -d djangojs parameter, like this:

django-admin makemessages -d djangojs -l de

This would create or update the message file for JavaScript for German. After updating message files, just run django-admin compilemessages the same way as you do with normal Django message files.

`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 the GNOME servershttps://download.gnome.org/binaries/win32/dependencies/
- gettext-runtime-X.zip
- gettext-tools-X.zip
X is the version number, we are requiring 0.15 or higher.
Extract the contents of the bin directories in both files to the same folder on your system (i.e. C:ProgramFilesgettext-utils)
Update the system PATH:
- Control Panel > System > Advanced > Environment Variables.
- In the System variables list, click Path, click Edit.
- Add ;C:Program Filesgettext-utilsin at the end of the Variable value field.

You may also use gettext binaries you have obtained elsewhere, so long as the xgettext --version command works properly. Do not attempt to use Django translation utilities with a gettext package if the commandxgettext --version entered at a Windows command prompt causes a popup window saying xgettext.exe has generated errors and will be closed by Windows.

Customizing the `makemessages` command

If you want to pass additional parameters to xgettext, you need to create a custom makemessages command and override its xgettext_options attribute:

from django.core.management.commands import makemessages

class Command(makemessages.Command):
    xgettext_options = makemessages.Command.xgettext_options + ["--keyword=mytrans"]

If you need more flexibility, you could also add a new argument to your custom makemessages command:

from django.core.management.commands import makemessages

class Command(makemessages.Command):

    def add_arguments(self, parser):
        s			
                
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Chapter 20: Internationalizati

Definitions

Translation

Internationalization: in Python code

Standard translation

Comments for translators

Marking strings as no-op

Pluralization

Contextual markers

Lazy translation

MODEL FIELDS AND RELATIONSHIPS VERBOSE_NAME AND HELP_TEXT OPTION VALUES

MODEL VERBOSE NAMES VALUES

MODEL METHODS SHORT_DESCRIPTION ATTRIBUTE VALUES

Working with lazy translation objects

LAZY TRANSLATIONS AND PLURAL

JOINING STRINGS: STRING_CONCAT()

OTHER USES OF LAZY IN DELAYED TRANSLATIONS

Localized names of languages

Internationalization: in template code

trans template tag

blocktrans template tag

String literals passed to tags and filters

Comments for translators in templates

Switching language in templates

Other tags

Internationalization: in JavaScript code

The javascript_catalog view

Using the JavaScript translation catalog

Note on performance

Internationalization: in URL patterns

Language prefix in URL patterns

Translating URL patterns

Reversing in templates

Localization: how to create language files

Message files

Compiling message files

Creating message files from JavaScript source code

gettext on Windows

Customizing the makemessages command

MODEL FIELDS AND RELATIONSHIPS `VERBOSE_NAME` AND `HELP_TEXT` OPTION VALUES

MODEL METHODS `SHORT_DESCRIPTION` ATTRIBUTE VALUES

`trans` template tag

`blocktrans` template tag

The `javascript_catalog` view

`gettext` on Windows

Customizing the `makemessages` command