Two days ago, I started to create another Google App Engine application. This application will be internationalized when its 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 incorporate with Django partially.
The goal here is:
- Use minimal Django stuff, only import the essential stuff in order to get Djangos 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 http://yjltest.appspot.com/i18n.
Note
http://yjltest.appspot.com/i18n is gone. (2015-12-14T06:40:18Z)
Before we go into the code, please read the I18N and Settings of Django.
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.
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'
Wraps those need to be translated with _("message") in Python script and {% trans "message" %} in template files. Please read I18N for more usages.
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.
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.
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.
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.
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').
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 isnt a good solution for I18N in Google App Engine if Google doesnt natively support it.
- 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.
