Internationalization And Localization

Status:

Work in progress

Turbogears2 relies on Babel for i18n and l10n support. So if this document is not enough you will want to check their respective documentation:

• Babel’s UserGuide

A quickstarted project comes fully i18n enabled so you should get started quickly.

If the quickstarted project includes a catalog for your browser language, its generated welcome page can be displayed in that language.

Language Auto-Select

Turbogears2 contains the logic to setup request’s language based on browser’s preferences(*).

[*] - Every modern browser sends a special header along with every web request which tells the server which language it would prefer to see in a response.

The language in use during the request is available through the tg.i18n.get_lang() function. This will report the currently selected languages both in case of an auto-detected language preference or in case of languages forced by the developer.

Languages returned by tg.i18n.get_lang() are ordered by user preference. By default all the requested languages are returned, if you want to get only the ones your application supports call get_lang(all=False).

The current language in use is usually get_lang(all=False)[0].

Forcing a Language

Developers can force the currently used language for each request using the tg.i18n.set_request_lang() function. This changes the language only for the current request.

If you need to permanently change the language for the user session duration, tg.i18n.set_lang() can be used. If TurboGears session support is enabled it will store the choosen language inside the session and recover it whenever the user comes back on next request.

Making your code international

Whenever you write a message that has to displayed you must let TurboGears know that it has to be translated.

Even though TurboGears is able to automatically detect content inside tags and mark them for translation all the strings inside controllers must be explicitly marked as translated.

This can be achieved with the tg.i18n.ugettext() and tg.i18n.lazy_ugettext() calls which are usually imported with _ and l_ names:

from tg.i18n import ugettext as _

class RootController(BaseController):
    @expose('myproj.templates.index')
    def index(self):
        return dict(msg=_('Hello World'))

In the previous example the ‘Hello World’ string will be detect by TurboGears when collecting translatable text and will display in the browser language if a translation for that language is available.

While ugettext() works perfectly to translate strings inside a request it does not allow translating strings outside a request. This is due to the fact that TurboGears won’t know the browser language when there isn’t a running request. To translate global variables, parameters default values or any other string which is created outside a controller method the lazy_ugettext method must be used:

from tg.i18n import lazy_ugettext as l_

class RootController(BaseController):
    @expose('myproj.templates.index')
    def index(self, msg=l_('Hello World')):
        return dict(msg=msg)

In this case the msg parameter is translated using lazy_ugettext() as it is constructed at controller import time when no request is available. This will create an object that will translate the given string only when the string itself is displayed or evaluated.

Keep in mind that as the lazy string object built by lazy_ugettext() is translated whenever the string is evaluated joining strings or editing it will force the translation. So the resulting object must still be evaluated only inside a request or it will always be translated to the default project language only.

An i18n Quick Start

Quickstarted projects store their i18n defaults in pyproject.toml. The [tool.tg.devtools.i18n] section configures the catalog domain, locale directory, and generated POT file. The [tool.babel] section contains the Babel extraction mappings that tell Babel which files should be searched for translatable strings.

TurboGears uses Babel through the gearbox i18n command to extract messages to a POT file in your project’s package i18n directory. Install the generated project into the active environment before running gearbox i18n commands so that the project-provided command is available:

python -m pip install -e .

Don’t forget to add the generated catalog files to your revision control system if you use one.

1. Extract all the translatable strings from your project’s files by using the following command:

gearbox i18n extract

This command will generate a “pot” file in the i18n folder of your application. This pot file is the reference file that serves for all the different translations.

2. Create a translation catalog for your language, let’s take ‘zh_tw’ for example:

gearbox i18n init -l zh_tw

3. Edit your language catalog in [package]/i18n/[locale]/LC_MESSAGES/[domain].po. For example, a project whose package and catalog domain are both myproject will create myproject/i18n/zh_tw/LC_MESSAGES/myproject.po.

If you’re not an expert in i18n or if you would like to give the files to someone else so that he helps you we recommend that you use the really nice poedit program. This program works nicely on GNU/Linux and Windows and provides a nice user-interface to edit po files.

4. Compile your lang:

   gearbox i18n compile
   

5. Configure the default language in development.ini if you want to force one instead of using browser language negotiation:

[app:main]
i18n.lang = zh_tw

6. Start server:

   gearbox serve --reload
   

And see the local message show on the screen.

Commands

To fresh start a translation, you could use the following command to handle your locales:

Init Catalog

Create a catalog for a new locale with the following command:

gearbox i18n init -l [locale]

The locale could be es (Spanish), fr (French), zh_tw (Taiwan), ja (Japanese), ru (Russian), or any other locale recognized by Babel.

Extract Messages

Extract all messages from the project with the following command:

gearbox i18n extract

Update Catalog

Update an existing catalog after extracting new messages with the following command:

gearbox i18n update -l [locale]

Compile Catalog

Compile catalogs with the following command:

gearbox i18n compile