Nova uses the oslo.i18n library to support internationalization. The oslo.i18n library is built on top of gettext 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/ 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})


LOG.warning(_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