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1   Setting Up

We need to use Django Settings to make I18N work. The reason of using Setting was due to Djangos gettext helper will require Settings module and decide location of message files by the location of Settings module.

If we want to use Django Setting, we must run the following code:

from google.appengine.ext.webapp import template

os.environ['DJANGO_SETTINGS_MODULE'] = 'conf.settings'
from django.conf import settings
# Force Django to reload settings
settings._target = None

Note that you must import the google.appengine.ext.webapp.template module, or you might get error about conf.settings is not able to be imported.

We need to set the environment variable DJANGO_SETTINGS_MODULE to the location of Setting module, conf.settings in this case. conf is the package and settings is a module file, our Settings module.

Why conf? Because when we generate message files from Python scripts and templates we will see how to generate later, the Django message file generator, make-messages.py, will create files under conf/locale/ from where its run.

2   Settings

What do we need in conf/settings.py?

USE_I18N = True

# Valid languages
LANGUAGES = (
    # 'en', 'zh_TW' match the directories in conf/locale/*
    ('en', _('English')),
    ('zh_TW', _('Chinese')),

    # or ('zh-tw', _('Chinese')), # But the directory must still be conf/locale/zh_TW

    )# This is a default languageLANGUAGE_CODE = 'en'

3   Mark the messages

Wraps those need to be translated with _("message") in Python script and {% trans "message" %} in template files. Please read I18N¹ for more usages.

4   Generate message files

Before you run the helper script, we need to create conf/locale, the helper wont create it for us.

Make sure you are at root of Google App Engine applications directory, then run:

$ PYTHONPATH=/path/to/googleappengine/python/lib/django/ /path/to/googleappengine/python/lib/django/django/bin/make-messages.py -l en

/path/to/googleappengine/ is the Google App Engine SDKs location. This command should generate the conf/locale/en/LC_MESSAGE/django.po. Now you can open it to translate.

Dont forget to set CHARSET, Usually UTF-8 will be fine, the line would read like:

"Content-Type: text/plain; charset=UTF-8\n"

Once you finish translating, you need to run:

$ PYTHONPATH=/path/to/python/googleappengine/lib/django/ /path/to/googleappengine/python/lib/django/django/bin/compile-messages.py

It will generate django.mo files in each language directories. You also need to update when you modify scripts or template, run:

$ PYTHONPATH=/path/to/googleappengine/python/lib/django/ /path/to/googleappengine/python/lib/django/django/bin/make-messages.py -a

This will update all languages in conf/locale.

5   Working?

If you run your application, now it should show the language in conf.settings.LANGUAGE_CODE.

This is a per application setting, which is not normally that we want. We will expect each user can choose their own language. Django has a helper that calls LocaleMiddleware can do the job, unfortunately, it needs Djangos request and response class to work normally.

6   Do the dirty job

In order to do what LocaleMiddleware does, we need to make Google App Engines request/response objects have same behavior as Djagnos. For easing the complexity, we create a new class, I18NRequestHandler, which inherits google.ext.webapp.RequestHandler. You only need to replace with it in your handlers.

import os

from google.appengine.ext import webapp
from django.utils import translation

class I18NRequestHandler(webapp.RequestHandler):

  def initialize(self, request, response):

    webapp.RequestHandler.initialize(self, request, response)

    self.request.COOKIES = Cookies(self)
    self.request.META = os.environ
    self.reset_language()

  def reset_language(self):

    # Decide the language from Cookies/Headers
    language = translation.get_language_from_request(self.request)
    translation.activate(language)
    self.request.LANGUAGE_CODE = translation.get_language()

    # Set headers in response
    self.response.headers['Content-Language'] = translation.get_language()
#    translation.deactivate()

Where Cookies is from http://appengine-cookbook.appspot.com/recipe/a-simple-cookie-class/ (dead link with long gone Cookbook). When request comes in, it can automatically activate the language from what Cookies/Headers specify.

7   Caching problem

Its not so perfect. I have noticed a problem in development server. If you change code and/or the message file, recompile the message file while server still runs, those message in entry script may not be translated for reflecting to cookie django_languages change. I believe that is about the caching.

I am not sure the natural problems, so I couldnt solve it. However, this may not be severe problem.

8   Encoding

If you use unicode string (not str string) in {% blocktrans %} template tag, you may get error, encode it to utf-8 first, e.g. s.encode('utf-8').

9   Language Code

You must use underscore not dash for messages directory, e.g aa_BB, or Django would not recognize directory named as aa-BB or aa-bb. But in conf.settings you can use aa-bb, this means the language code and directory can be different, e.g. zh-tw for the language code in Python and zh_TW as message directory name.

10   Conclusion

Although this will work, but it may be broken if any changes to Django framework within Google App Engine. There isnt a good solution for I18N in Google App Engine if Google doesnt natively support it.

11   Updates

• 2009-11-25: Added not about template module first and encoding issue, and updated the path of Python lib in GAE SDK.
• 2009-12-24: Added a note about Language Code format, thanks BRAGA, again.
• 2010-02-04: Added a note about the Language Code and message directory name.
• 2013-02-17: fix dead links and typos.
• 2013-07-24: remove .rst from title, update link.