Internationalization
====================

Nova uses the `oslo.i18n library
<http://docs.openstack.org/developer/oslo.i18n/index.html>`_ to support
internationalization. The oslo.i18n library is built on top of `gettext
<http://docs.python.org/library/gettext.html>`_ and provides functions that are
used to enable user-facing strings such as log messages to appear in the
appropriate language in different locales.

Nova exposes the oslo.i18n library support via the ``nova/i18n.py`` integration
module. This module provides the functions needed to wrap translatable strings.
It provides the ``_()`` wrapper for general user-facing messages and specific
wrappers for messages used only for logging. DEBUG level messages do not need
translation but CRITICAL, ERROR, WARNING and INFO messages should be wrapped
with ``_LC()``, ``_LE()``, ``_LW()`` or ``_LI()`` respectively.

For example::

    LOG.debug("block_device_mapping %(mapping)s",
              {'mapping': block_device_mapping})

or::

    LOG.warn(_LW('Unknown base file %(img)s'), {'img': img})

You should use the basic wrapper ``_()`` for strings which are not log
messages::

    raise nova.SomeException(_('Invalid service catalogue'))

Do not use ``locals()`` for formatting messages because:
1. It is not as clear as using explicit dicts.
2. It could produce hidden errors during refactoring.
3. Changing the name of a variable causes a change in the message.
4. It creates a lot of otherwise unused variables.

If you do not follow the project conventions, your code may cause hacking
checks to fail.

The ``_()``, ``_LC()``, ``_LE()``, ``_LW()`` and ``_LI()`` functions can be
imported with::

    from nova.i18n import _
    from nova.i18n import _LC
    from nova.i18n import _LE
    from nova.i18n import _LW
    from nova.i18n import _LI