The goal of internationalization is to allow a single Web application to offer its content and functionality in multiple languages and locales.
For text translations, you, the Django developer, can accomplish this goal by adding a minimal amount of hooks to your Python 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.” It’s your responsibility to mark translatable strings; the system can only translate strings it knows about.
Django takes care of using these hooks to translate Web apps, on the fly, according to users’ language preferences.
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:
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 %(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 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 wouldn't be able to reorder placeholder text.
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.")
This also works in templates with the comment tag:
{% comment %}Translators: This is a text of the base template {% endcomment %}
The comment will then appear in the resulting .po file and should also be displayed by most translation tools.
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.
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
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.
Lets see a slightly more complex usage example:
from django.utils.translation import ungettext
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
}
Here we reuse localizable, hopefully already translated literals (contained in the verbose_name and verbose_name_plural model Meta options) for other parts of the sentence so all of it is consistently based on the cardinality of the elements at play.
Note
When using this technique, make sure you use a single name for every extrapolated variable included in the literal. In the example above note how we used the name Python variable in both translation strings. This example would fail:
from django.utils.translation import ungettext
from myapp.models import Report
count = Report.objects.count()
d = {
'count': count,
'name': Report._meta.verbose_name,
'plural_name': Report._meta.verbose_name_plural
}
text = ungettext(
'There is %(count)d %(name)s available.',
'There are %(count)d %(plural_name)s available.',
count
) % d
You would get a a format specification for argument 'name', as in 'msgstr[0]', doesn't exist in 'msgid' error when running django-admin.py compilemessages.
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 the django.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.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 ""
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.
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 doesn't know how to convert itself to a bytestring. You can't 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.
u"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)
"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. That's a bug in your code.
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 Django models. Field names and table names should be marked for translation (otherwise, they won't be translated in the admin interface). This means writing explicit verbose_name and verbose_name_plural options in the Meta class, though, rather than relying on Django's default determination of verbose_name and verbose_name_plural by looking at the model's class name:
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')
Your model classes may not only contain normal fields: you may have relations (with a ForeignKey field) or additional model methods you may use for columns in the Django admin site.
If you have models with foreign keys and you use the Django admin site, you can provide translations for the relation itself by using the verbose_name parameter on the ForeignKey object:
class MyThing(models.Model):
kind = models.ForeignKey(ThingKind, related_name='kinds',
verbose_name=_('kind'))
As you would do for the verbose_name and verbose_name_plural settings of a model Meta class, you should provide a lowercase verbose name text for the relation as Django will automatically titlecase it when required.
For model methods, you can provide translations to Django and the admin site with the short_description parameter set on the corresponding method:
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?')
As always with model classes translations, don't forget to use the lazy translation method!
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.
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 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.
Translations in Django templates uses two template tags and a slightly different syntax than in Python code. To give your template access to these tags, put {% load i18n %} toward the top of your template.
The {% trans %} template tag translates 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.
It's not possible to mix a template variable inside a string within {% trans %}. If your translations require strings with variables (placeholders), use {% blocktrans %} instead.
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 and 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 and author|title as author_t %}
This tag also provides for pluralization. To use it:
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 %}
Each RequestContext has access to three translation-specific variables:
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).
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 nested tuples, {% get_language_info_list %} supports simple lists of language codes. If you do this in your view:
return render_to_response('mytemplate.html', {
'available_languages': ['en', 'es', 'fr'],
}, RequestContext(request))
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:
Adding translations to JavaScript poses some problems:
Django provides an integrated solution for these problems: It passes the translations into JavaScript, so you can call gettext, etc., from within JavaScript.
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:
js_info_dict = {
'packages': ('your.app.package',),
}
urlpatterns = patterns('',
(r'^jsi18n/$', 'django.views.i18n.javascript_catalog', js_info_dict),
)
Each string in packages should be in Python dotted-package syntax (the same format as the strings in INSTALLED_APPS) and should refer to a package that contains a locale directory. If you specify multiple packages, all those catalogs are merged into one catalog. This is useful if you have JavaScript that uses strings from different applications.
The precedence of translations is such that the packages appearing later in the packages argument have higher precedence than the ones appearing at the beginning, this is important in the case of clashing translations for the same literal.
By default, the view uses the djangojs gettext domain. This can be changed by altering the domain argument.
You can make the view dynamic by putting the packages into the URL pattern:
urlpatterns = patterns('',
(r'^jsi18n/(?P<packages>\S+?)/$', '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.
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.
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. 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).
As a convenience, Django comes with a view, django.views.i18n.set_language(), that sets a user's language preference and redirects back to the previous page.
Activate this view by adding the following line to your URLconf:
(r'^i18n/', include('django.conf.urls.i18n')),
(Note that this example makes the view available at /i18n/setlang/.)
The view expects to be called via the POST method, with a language parameter set in request. If session support is enabled, the view saves the language choice in the user's session. Otherwise, it saves the language choice in a cookie that is by default named django_language. (The name can be changed through the LANGUAGE_COOKIE_NAME setting.)
After setting the language choice, Django redirects the user, following this algorithm:
Here's example HTML template code:
<form action="/i18n/setlang/" method="post">
{% csrf_token %}
<input name="next" type="hidden" value="/next/page/" />
<select name="language">
{% get_language_info_list for LANGUAGES as languages %}
{% for language in languages %}
<option value="{{ language.code }}">{{ language.name_local }} ({{ language.code }})</option>
{% endfor %}
</select>
<input type="submit" value="Go" />
</form>
Dec 26, 2011