path: root/docs/narr/i18n.rst

.. index::
   single: i18n
   single: l10n
   single: internationalization
   single: localization

.. _i18n_chapter:

Internationalization and Localization
=====================================

:term:`Internationalization` (i18n) is the act of creating software
with a user interface that can potentially be displayed in more than
one language or cultural context.  :term:`Localization` (l10n) is the
process of displaying the user interface of an internationalized
application in a *particular* language or cultural context.

:mod:`repoze.bfg` offers internationalization and localization
subsystems that can be used to translate the text of buttons, error
messages and other software- and template-defined values into the
native language of a user of your application.

.. note: The APIs and functionality described in this chapter are new
   as of :mod:`repoze.bfg` version 1.3.

.. index::
   single: translation string
   pair: domain; translation
   pair: msgid; translation
   single: message identifier

Creating a Translation String
-----------------------------

While you write your software, you can insert specialized markup into
your Python code that makes it possible for the system to translate
text values into the languages used by your application's users.  This
markup creates a :term:`translation string`.  A translation string is
an object that behave mostly like a normal Unicode object, except that
it also carries around extra information related to its job as part of
the :mod:`repoze.bfg` translation machinery.

Using The ``TranslationString`` Class
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

The most primitive way to create a translation string is to use the
:class:`repoze.bfg.i18n.TranslationString` callable:

.. code-block:: python
   :linenos:

   from repoze.bfg.i18n import TranslationString
   ts = TranslationString('Add')

This creates a Unicode-like object that is a TranslationString.

.. note::

   For people more familiar with :term:`Zope` i18n, a TranslationString
   is a lot like a ``zope.i18nmessageid.Message`` object.  It is not a
   subclass, however.  For people more familiar with :term:`Pylons` or
   :term:`Django` i18n, using a TranslationString is a lot like using
   "lazy" versions of related gettext APIs.

The first argument to :class:`repoze.bfg.i18n.TranslationString` is
the ``msgid``; it is required.  It represents the key into the
translation mappings provided by a particular localization. The
``msgid`` argument must be a Unicode object or an ASCII string.  The
msgid may optionally contain *replacement markers*.  For instance:

.. code-block:: python
   :linenos:

   from repoze.bfg.i18n import TranslationString
   ts = TranslationString('Add ${number}')

Within the string above, ``${stuff}`` is a replacement marker.  It
will be replaced by whatever is in the *mapping* for a translation
string.  The mapping may be supplied at the same time as the
replacement marker itself:

.. code-block:: python
   :linenos:

   from repoze.bfg.i18n import TranslationString
   ts = TranslationString('Add ${number}', mapping={'number':1})

Any number of replacement markers can be present in the msgid value,
any number of times.  Only markers which can be replaced by the values
in the *mapping* will be replaced at translation time.  The others
will not be interpolated and will be output literally.

A translation string should also usually carry a *domain*.  The domain
represents a translation category to disambiguate it from other
translations of the same msgid, in case they conflict.

.. code-block:: python
   :linenos:

   from repoze.bfg.i18n import TranslationString
   ts = TranslationString('Add ${number}', mapping={'number':1}, 
                          domain='form')

The above translation string named a domain of ``form``.  A
:term:`translator` function will often use the domain to locate the
right translator file on the filesystem which contains translations
for a given domain.  In this case, if it were trying to translate to
our msgid to German, it might try to find a translation from a
:term:`gettext` file within a :term:`translation directory` like this
one::

   locale/de/LC_MESSAGES/form.mo

In other words, it would want to take translations from the ``form.mo``
translation file in the German language.

Finally, the TranslationString constructor accepts a ``default``
argument.  If a ``default`` argument is supplied, it replaces usages
of the ``msgid`` as the *default value* for the translation string.
When ``default`` is ``None``, the ``msgid`` value passed to a
TranslationString is used as an implicit message identifier.  Message
identifiers are matched with translations in translation files, so it
is often useful to create translation strings with "opaque" message
identifiers unrelated to their default text:

.. code-block:: python
   :linenos:

   from repoze.bfg.i18n import TranslationString
   ts = TranslationString('add-number', default='Add ${number}',
                           domain='form', mapping={'number':1})

When default text is used, Default text objects may contain
replacement values.

.. index::
   single: translation string factory

Using the ``TranslationStringFactory`` Class
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Another way to generate a translation string is to use the
:attr:`repoze.bfg.i18n.TranslationStringFactory` object.  This object
is a *translation string factory*.  Basically a translation string
factory presets the ``domain`` value of any :term:`translation string`
generated by using it.  For example:

.. code-block:: python
   :linenos:

   from repoze.bfg.i18n import TranslationStringFactory
   _ = TranslationStringFactory('bfg')
   ts = _('Add ${number}', msgid='add-number', mapping={'number':1})

.. note:: We assigned the translation string factory to the name
   ``_``.  This is a convention which will be supported by translation
   file generation tools.

After assigning ``_`` to the result of a
:func:`repoze.bfg.i18n.TranslationStringFactory`, the subsequent
result of calling ``_`` will be a
:class:`repoze.bfg.i18n.TranslationString` instance.  Even though a
``domain`` value was not passed to ``_`` (as would have been necessary
if the :class:`repoze.bfg.i18n.TranslationString` constructor were
used instead of a translation string factory), the ``domain``
attribute of the resulting translation string will be ``bfg``.  As a
result, the previous code example is completely equivalent (except for
spelling) to:

.. code-block:: python
   :linenos:

   from repoze.bfg.i18n import TranslationString as _
   ts = _('Add ${number}', msgid='add-number', mapping={'number':1}, 
          domain='bfg')

You can set up your own translation string factory much like the one
provided above by using the
:class:`repoze.bfg.i18n.TranslationStringFactory` class.  For example,
if you'd like to create a translation string factory which presets the
``domain`` value of generated translation strings to ``form``, you'd
do something like this:

.. code-block:: python
   :linenos:

   from repoze.bfg.i18n import TranslationStringFactory
   _ = TranslationStringFactory('form')
   ts = _('Add ${number}', msgid='add-number', mapping={'number':1})

Creating a unique domain for your application via a translation string
factory is best practice.  Using your own unique translation domain
allows another person to reuse your application without needing to
merge your translation files with his own.  Instead, he can just
include your package's :term:`translation directory` via the
:meth:`repoze.bfg.configuration.Configurator.add_translation_dirs`
method.

.. note::

   For people familiar with Zope internationalization, a
   TranslationStringFactory is a lot like a
   ``zope.i18nmessageid.MessageFactory`` object.  It is not a
   subclass, however.

.. index::
   single: gettext
   single: translation directories

Working With ``gettext`` Translation Files
------------------------------------------

Once your application source code files and templates are marked up
with translation markers, you can work on translations.

.. note::

   The steps a developer must take to work with :term:`gettext`
   :term:`message catalog` files within a :mod:`repoze.bfg`
   application are very similar to the steps a :term:`Pylons`
   developer must take to do the same.  See the `Pylons
   internationalization documentation
   <http://wiki.pylonshq.com/display/pylonsdocs/Internationalization+and+Localization>`_
   for more information.

.. index::
   single: Babel

.. _installing_babel:

Installing Babel
~~~~~~~~~~~~~~~~

In order for the commands related to working with ``gettext``
translation files to work properly, you will need to have
:term:`Babel` installed into the same environment in which
:mod:`repoze.bfg` is installed.

Installation on UNIX
++++++++++++++++++++

If the :term:`virtualenv` into which you've installed your
:mod:`repoze.bfg` application lives in ``/my/virtualenv``, you can
install Babel like so:

.. code-block:: bash

   $ cd /my/virtualenv
   $ bin/easy_install Babel

Installation on Windows
+++++++++++++++++++++++

If the :term:`virtualenv` into which you've installed your
:mod:`repoze.bfg` application lives in ``C:\my\virtualenv``, you can
install Babel like so:

.. code-block:: bash

   C> cd \my\virtualenv
   C> bin\easy_install Babel

.. index::
   single: Babel; message extractors

Changing the ``setup.py``
+++++++++++++++++++++++++

You need some "hair" to your application's ``setup.py`` file (see
:ref:`project_narr` for information about the composition of an
application's ``setup.py`` file).  In particular, add the ``Babel``
distribution to your application's ``install_requires`` list and
insert a set of references to :term:`Babel` *message extractors*
within the call to :func:`setuptools.setup`:

.. code-block:: python
   :linenos:

    setup(name="mypackage",
          ...
          install_requires = [
                ....
                "Babel",
                ],
          message_extractors = { ".": [
                ("**.py",   "chameleon_python", None ),
                ("**.pt",   "chameleon_xml", None ),
                ]},
          )

The ``message_extractors`` stanza placed into the ``setup.py`` file
cause the :term:`Babel` message catalog extraction machinery to also
consider ``**.pt`` files when doing message id extraction.

.. index::
   pair: extracting; messages

Extracting Messages from Code and Templates
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Once :term:`Babel` is installed and your application's ``setup.py``
file has the correct message extractor references, you may extract a
message catalog template from the code and :term:`Chameleon` templates
which reside in your :mod:`repoze.bfg` application.  You run a
``setup.py`` command to extract the messages:

.. code-block:: bash
   :linenos:

   $ cd /place/where/myapplication/setup.py/lives
   $ mkdir -p myapplication/locale
   $ python setup.py extract_messages

The message catalog template will end up in
``myapplication/locale/myapplication.pot``.

.. index::
   pair: initializing; message catalog

Initializing a Message Catalog File
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Initialize a message catalog for a specific locale from a
pre-generated ``.pot`` template::

   $ cd /place/where/myapplication/setup.py/lives
   $ python setup.py init_catalog -l es

The message catalog ``.po`` file will end up in
``myapplication/locale/es/LC_MESSAGES/myapplication.po``.

XXX finish

.. index::
   pair: updating; message catalog

Updating a Catalog File
~~~~~~~~~~~~~~~~~~~~~~~

Update ``.po`` files based on changes to the ``.pot`` file::

   $ cd /place/where/myapplication/setup.py/lives
   $ python setup.py update_catalog

XXX finish

.. index::
   pair: compiling; message catalog

Compiling a Message Catalog File
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Compile ``.po`` files to ``.mo`` files::

   $ cd /place/where/myapplication/setup.py/lives
   $ python setup.py compile_catalog

XXX finish

.. index::
   single: localizer
   single: get_localizer

Using a Localizer
-----------------

A :term:`localizer` is an object that allows you to perform
translation or pluralization "by hand" in an application.  You may use
the :func:`repoze.bfg.i18n.get_localizer` function to obtain a
:term:`localizer`.  :func:`repoze.bfg.i18n.get_localizer`. This
function will return either the localizer object implied by the active
:term:`locale negotiator` or a default localizer object if no explicit
locale negotiator is registered.

.. code-block:: python
   :linenos:

   from repoze.bfg.i18n import get_localizer

   def aview(request):
       locale = get_localizer(request)

.. index::
   single: translating (i18n)

.. _performing_a_translation:

Performing a Translation
~~~~~~~~~~~~~~~~~~~~~~~~

A :term:`localizer` has a ``translate`` method which accepts either a
:term:`translation string` or a Unicode string and which returns a
Unicode object representing the translation.  So, generating a
translation in a view component of an application might look like so:

.. code-block:: python
   :linenos:

   from repoze.bfg.i18n import get_localizer
   from repoze.bfg.i18n import TranslationString

   ts = TranslationString('Add ${number}', mapping={'number':1}, domain='bfg')

   def aview(request):
       localizer = get_localizer(request)
       translated = localizer.translate(ts) # translation string
       # ... use translated ...

The :func:`repoze.bfg.i18n.get_localizer` function will return a
:class:`repoze.bfg.i18n.Localizer` object bound to the locale name
represented by the request.  The translation returned from its
:meth:`repoze.bfg.i18n.Localizer.translate` method will depend on the
``domain`` attribute of the provided translation string as well as the
locale of the localizer.

.. note:: If you're using :term:`Chameleon` templates, you don't need
   to pre-translate translation strings this way.  See
   :ref:`chameleon_translation_strings`.

.. index::
   single: pluralizing (i18n)

.. _performing_a_pluralization:

Performing a Pluralization
~~~~~~~~~~~~~~~~~~~~~~~~~~

A :term:`localizer` has a ``pluralize`` method with the following
signature:

.. code-block:: python
   :linenos:

   def pluralize(singular, plural, n, domain=None, mapping=None):
       ...

The ``singular`` and ``plural`` arguments should each be a Unicode
value representing a :term:`message identifier`.  ``n`` should be an
integer.  ``domain`` should be a :term:`translation domain`, and
``mapping`` should be a dictionary that is used for *replacement
value* interpolation of the translated string.  If ``n`` is plural
for the current locale, ``pluralize`` will return a Unicode
translation for the message id ``plural``, otherwise it will return a
Unicode translation for the message id ``singular``.

The arguments provided as ``singular`` and/or ``plural`` may also be
:term:`translation string` objects, but the domain and mapping
information attached to those object is ignored.

.. code-block:: python
   :linenos:

   from repoze.bfg.i18n import get_localizer

   def aview(request):
       localizer = get_localizer(request)
       translated = localizer.pluralize('Item', 'Items', 1, 'mydomain')
       # ... use translated ...

.. index::
   single: locale name
   single: get_locale_name
   single: negotiate_locale_name

.. _obtaining_the_locale_name:

Obtaining the Locale Name for a Request
---------------------------------------

You can obtain the locale name related to a request by using the
:func:`repoze.bfg.i18n.get_locale_name` function.

.. code-block:: python
   :linenos:

   from repoze.bfg.i18n import get_locale_name

   def aview(request):
       locale_name = get_locale_name(request)

This returns the locale name negotiated by the currently active
:term:`locale negotiator` or the default locale name (usually ``en``)
if no locale negotiator is configured.  You can change the default
locale name by changing the ``default_locale_name`` setting; see
:ref:`default_locale_name_setting`.

Once :func:`repoze.bfg.i18n.get_locale_name` has run once, the local
name is stored on the request object it is passed.  Subsequent calls
to :func:`repoze.bfg.i18n.get_locale_name` will return the stored
locale name without invoking the :term:`locale negotiator`.  To
avoid this caching, you can use the
:func:`repoze.bfg.i18n.negotiate_locale_name` function:

.. code-block:: python
   :linenos:

   from repoze.bfg.i18n import negotiate_locale_name

   def aview(request):
       locale_name = negotiate_locale_name(request)

You can also obtain the locale name related to a request using the
``locale_name`` attribute of a :term:`localizer`.

.. code-block:: python
   :linenos:

   from repoze.bfg.i18n import get_localizer

   def aview(request):
       localizer = get_localizer(request)
       locale_name = localizer.locale_name

Obtaining the locale name as an attribute of a localizer is equivalent
to obtaining a locale name by calling the
:func:`repoze.bfg.i18n.get_locale_name` function.

.. index::
   single: date and currency formatting (i18n)
   single: Babel

Performing Date Formatting and Currency Formatting
--------------------------------------------------

:mod:`repoze.bfg` does not itself perform date and currency formatting
for different locales.  However, :term:`Babel` can help you do this
via the :class:`babel.core.Locale` class.  The `Babel documentation
for this class
<http://babel.edgewall.org/wiki/ApiDocs/babel.core#babel.core:Locale>`_
provides minimal information about how to perform date and currency
related locale operations.  See :ref:`installing_babel` for
information about how to install Babel.

The :class:`babel.core.Locale` class requires a :term:`locale name` as
an argument to its constructor. You can use :mod:`repoze.bfg` APIs to
obtain the locale name for a request to pass to the
:class:`babel.core.Locale` constructor; see
:ref:`obtaining_the_locale_name`.  For example:

.. code-block:: python
   :linenos:

   from babel.core import Locale
   from repoze.bfg.i18n import get_locale_name

   def aview(request):
       locale_name = get_locale_name(request)
       locale = Locale(locale_name)

.. index::
   pair: translation strings; Chameleon

.. _chameleon_translation_strings:

Chameleon Template Support for Translation Strings
--------------------------------------------------

When a :term:`translation string` is used as the subject of textual
rendering by a :term:`Chameleon` template renderer, it will
automatically be translated to the requesting user's language if a
suitable translation exists. This is true of both the ZPT and text
variants of the Chameleon template renderers.

For example, in a Chameleon ZPT template, the translation string
represented by "some_translation_string" in each example below will go
through translation before being rendered:

.. code-block:: xml
   :linenos:

   <span tal:content="some_translation_string"/>

.. code-block:: xml
   :linenos:

   <span tal:replace="some_translation_string"/>

.. code-block:: xml
   :linenos:

   <span>${some_translation_string}</span>

.. code-block:: xml
   :linenos:

   <a tal:attributes="href some_translation_string">Click here</a>
   XXX this appears to not yet work as of Chameleon 1.2.3

The features represented by attributes of the ``i18n`` namespace of
Chameleon will also consult the :mod:`repoze.bfg` translations.
See
`http://chameleon.repoze.org/docs/latest/i18n.html#the-i18n-namespace
<http://chameleon.repoze.org/docs/latest/i18n.html#the-i18n-namespace>`_.

.. note::

   Unlike when Chameleon is used outside of :mod:`repoze.bfg`, when it
   is used *within* :mod:`repoze.bfg`, it does not support use of the
   ``zope.i18n`` translation framework.  Applications which use
   :mod:`repoze.bfg` should use the features documented in this
   chapter rather than ``zope.i18n``.

Third party :mod:`repoze.bfg` template renderers might not provide
this support out of the box and may need special code to do an
equivalent.  For those, you can always use the more manual translation
facility described in :ref:`performing_a_translation`.

.. index::
   single: localization deployment settings
   single:  default_locale_name

.. _localization_deployment_settings:

Localization-Related Deployment Settings
----------------------------------------

A :mod:`repoze.bfg` application will have a ``default_locale_name``
setting.  This value represents the default locale name when no
:term:`locale negotiator` is registered.  Pass it to the
:mod:`repoze.bfg.configuration.Configurator` constructor at startup
time:

.. code-block:: python
   :linenos:

   from repoze.bfg.configuration import Configurator
   config = Configurator(settings={'default_locale_name':'de'})

You may alternately supply a ``default_locale_name`` via an
application's Paster ``.ini`` file:

.. code-block:: ini
   :linenos:

   [app:main]
   use = egg:MyProject#app
   reload_templates = true
   debug_authorization = false
   debug_notfound = false
   default_locale_name = de

If this value is not supplied via the Configurator constructor or via
a Paste onfig file, it will default to ``en``.

If this setting is supplied within the :mod:`repoze.bfg` application
``.ini`` file, it will be available as a settings key:

.. code-block:: python
   :linenos:

   from repoze.bfg.setttings import get_settings
   settings = get_settings()
   default_locale_name = settings['default_locale_name']

.. index::
   pair: translation; activating
   pair: locale; negotiator
   single: translation directory

.. _activating_translation:

Activating Translation
----------------------

By default, a :mod:`repoze.bfg` application performs no translation.
To turn translation on, you must do both of these two things:

- Add at least one :term:`translation directory` to your application.

- Configure a :term:`locale negotiator` into your application's
  configuration.

:term:`gettext` is the underlying machinery behind the
:mod:`repoze.bfg` translation machinery.  A translation directory is a
directory organized to be useful to :term:`gettext`.  A translation
directory usually includes a listing of language directories, each of
which itself includes an ``LC_MESSAGES`` directory.  Each
``LC_MESSAGES`` directory should contain one or more ``.mo`` files.
Each ``.mo`` file represents a :term:`message catalog`, which is used
to provide translations to your application.

A locale negotiator is a bit of code which accepts a request and which
returns a :term:`locale name`.  It is consulted when
:meth:`repoze.bfg.i18n.Localizer.translate` or
:meth:`repoze.bfg.i18n.Localizer.pluralize` is invoked.  It is also
consulted when :func:`repoze.bfg.i18n.get_locale_name` or
:func:`repoze.bfg.i18n.negotiate_locale_name` is invoked.

At the time of this writing, only one (very weak) built-in locale
negotiator implementation named
:class:`repoze.bfg.i18n.default_locale_negotiator` ships as part of
the :mod:`repoze.bfg` software.  This negotiator looks only at the the
``request.params['locale']`` value to determine the locale name.  You
can provide your own locale negotiator function as required.

Adding a Translation Directory
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

You may add a :term:`translation directory` to your application's
configuration either imperatively or via ZCML.  Adding a translation
directory registers all of its constituent :term:`message catalog`
files (all of the ``.mo`` files found within all ``LC_MESSAGES``
directories within each locale directory in the translation directory)
within your :mod:`repoze.bfg` application to be available to use for
translation services.

Imperative
++++++++++

You can add a translation directory imperatively by using the
:meth:`repoze.bfg.configuration.Configurator.add_translation_dirs`
during application startup.

For example:

.. code-block:: python
   :linenos:

   from repoze.bfg.configuration import Configurator
   from repoze.bfg.i18n import default_locale_negotiator
   config = Configurator(locale_negotiator=default_locale_negotiator)
   config.begin()
   config.add_translation_dirs('my.application:locale/', 
                               'another.application:locale/')
   config.end()

A message catalog in a translation directory added via
:meth:`repoze.bfg.configuration.Configurator.add_translation_dirs`
will be merged into translations from an message catalog added earlier
if both translation directories contain translations for the same
locale and :term:`translation domain`.

ZCML
++++

You can add a translation directory via ZCML by using the
:ref:`translationdir_directive` ZCML directive:

.. code-block:: xml
   :linenos:

   <translationdir dir="my.application:locale/"/>

A message catalog in a translation directory added via
:ref:`translationdir_directive` will be merged into translations from
an message catalog added earlier if both translation directories
contain translations for the same locale and :term:`translation
domain`.

.. _adding_a_locale_negotiator:

Adding a Locale Negotiator
~~~~~~~~~~~~~~~~~~~~~~~~~~

You may add a :term:`locale negotiator` either imperatively or via
ZCML.  A locale negotiator informs the operation of a
:term:`localizer` by telling it what :term:`locale name` is related to
a particular request.  See :ref:`creating_a_locale_negotiator`.

Imperative
++++++++++

Pass an object which can act as the negotiator as the
``locale_negotiator`` argument of the
:class:`repoze.bfg.configuration.Configurator` instance during
application startup.

For example:

.. code-block:: python
   :linenos:

   from repoze.bfg.configuration import Configurator
   from repoze.bfg.i18n import default_locale_negotiator
   config = Configurator(locale_negotiator=default_locale_negotiator)

Alternately, use the
:meth:`repoze.bfg.configuration.Configurator.set_locale_negotiator`
method.

For example:

.. code-block:: python
   :linenos:

   from repoze.bfg.configuration import Configurator
   from repoze.bfg.i18n import default_locale_negotiator
   config = Configurator()
   config.begin()
   config.set_locale_negotiator(default_locale_negotiator)
   config.end()

ZCML
++++

You can add a translation directory via ZCML by using the
:ref:`localenegotiator_directive` ZCML directive:

.. code-block:: xml
   :linenos:

   <localenegotiator negotiator="repoze.bfg.i18n.default_locale_negotiator"/>

.. _creating_a_locale_negotiator:

Creating a Locale Negotiator
----------------------------

A :term:`locale negotiator` is simply a callable which accepts a
request and returns a single :term:`locale name`.  Here's an
implementation of a simple locale negotiator:

.. code-block:: python
   :linenos:

    def default_locale_negotiator(request):
        locale_name = request.params.get('locale')
        if locale_name is None:
            settings = get_settings() or {}
            locale_name = settings.get('default_locale_name', 'en')
        return locale_name

Locale negotiation can be complex.  Your application may require a
policy-laden locale negotiator policy, so you can write your own and
supply it to an application configuration as per
:ref:`adding_a_locale_negotiator`.