Google App Engine应用国际化(i18n)支持解决方案

(This post is written only for Django 0.96.1 in GAE)

Two days ago, I started to create another Google App Engine application. This application will be internationalized when it’s finished. I tried searching for some solution, then I realized that there is no very simple way to achieve.

Normally, you can handle gettext stuff on your own, but our Google App Engine applications usually use templating from the SDK, which is from Django actually. One way or another, we have to incooperate with Django partially.

The goal here is:

  • Use minimal Django stuff, only import the essential stuff in order to get Django’s I18N support to work.
  • Messages in template must be translated, too.
  • Capable to decide the language from the cookie, django_language, or the request header, HTTP_ACCEPT_LANGUAGE.

I have already made a sample code, which you can read here and you can see it at

Before we go into the code, please read the I18N and Settings of Django.

Setting Up

We need to use Django Settings to make I18N work. The reason of using Setting was due to Django’s 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 varible 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,, will create files under conf/locale/ from where it’s run.


What do we need in conf/

USE_I18N = True

# Valid 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 language

Mark the messages

Wraps those need to be translated with _(“message”) in Python script and {% trans “message” %} in template files. Please read I18N for more usages.

Generate message files

Before you run the helper script, we need to create conf/locale, the helper won’t create it for us.

Make sure you are at root of Google App Engine application’s directory, then run

$ PYTHONPATH=/path/to/googleappengine/python/lib/django/ /path/to/googleappengine/python/lib/django/django/bin/ -l en

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

Don’t 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/

It will geneate 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/ -a

This will update all languages in conf/locale.


If you run you 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 Django’s request and response class to work normally.

Do the dirty job

In order to do what LocaleMiddleware does, we need to make Google App Engine’s request/response objects have same behavior as Djagno’s. 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

  def reset_language(self):

    # Decide the language from Cookies/Headers
    language = translation.get_language_from_request(self.request)
    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 When request comes in, it can automatically activate the language from what Cookies/Headers specify.

Caching problem

It’s 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_language’s change. I believe that is about the caching.

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


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’).

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.


Although this will work, but it may be broken if any changes to Django framework within Google App Engine. There isn’t a good solution for I18N in Google App Engine if Google doesn’t natively support it.

Updated on 2009-11-25: Added not about template module first and encoding issue, and updated the path of Python lib in GAE SDK.
Updated on 2009-12-24: Added a note about Language Code format, thanks BRAGA, again.
Updated on 2010-02-04: Added a note about the Language Code and message directory name.
Posted by livibetter at 2/25/2009 03:42:00 PM



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