zulip/docs/translating.md

# Translating Zulip

Zulip has full support for unicode, so you can already use your
preferred language everywhere in Zulip.

To make Zulip even better for users around the world, the Zulip UI is
being translated into a number of major languages, including Spanish,
German, French, Chinese, Russian, and Japanese, with varying levels of
progress.  If you speak a language other than English, your help with
translating Zulip would be greatly appreciated!

If you're interested in contributing translations to Zulip, join the
[Zulip project on Transifex](https://www.transifex.com/zulip/zulip/)
and ask to join any languages you'd like to contribute to (or add new
ones).  Transifex's notification system sometimes fails to notify the
maintainers when you ask to join a project, so please send a quick
email to zulip-core@googlegroups.com when you request to join the
project or add a language so that we can be sure to accept your
request to contribute.

## Setting Default Language in Zulip

Zulip allows you to set the default language through the settings
page under 'Display Settings' section.

## Translation Resource Files

All the translation magic happens through resource files which hold
the translated text. Backend resource files are located at
`static/locale/<lang_code>/LC_MESSAGES/django.po`, while frontend
resource files are localted at `static/locale/<lang_code>/translations.json`.
These files are uploaded to Transifex where they are translated. Once
translated, they are downloaded back into the codebase.

## Transifex Config

The config file that maps the resources from Zulip to Transifex is
located at `.tx/config`. Django  recognizes `zh_CN` instead of `zh-HANS`
for simplified Chinese language (this is fixed in Django 1.9). This
idiosyncrasy is also handled in the Transifex config file.

## Translation Process

The end-to-end process to get the translations working is as follows:

1. Mark the strings for translations (see sections for backend and
   frontend translations for details on this).

2. Create JSON formatted [resource][] files using the `python manage makemessages`
   command. This command will create a resource file called `translations.json`
   for frontend and `django.po` for backend for every language under
   `static/locale`. The location for frontend resource file can be
   changed by passing an argument to the command (see the help for the
   command for further details). However, make sure that the location
   is publicly accessible since frontend files are loaded through XHR
   in the frontend which will only work with publicly accessible resources.

   The `makemessages` command is idempotent in that:

   - It will only delete singular keys in the resource file when they
     are no longer used in Zulip code.
   - It will only delete plural keys (see below for the documentation
     on plural translations) when the corresponding singular key is
     absent.
   - It will not override the value of a singular key if that value
     contains a translated text.

3. Upload the resource files to Transifex using the `tx push -s -a`
   command.

4. Download the updated resource files from Transifex using the
   `tx pull -a` command. This command will download the resource files
   from Transifex and replace your local resource files with them.

## Backend Translations

All user-facing text in the Zulip UI should be generated by an HTML
template so that it can be translated.

Zulip uses two types of templates: backend templates (powered by the
[Jinja2][] template engine, though the original [Django][] template
engine is still supported) and frontend templates (powered by
[Handlebars][]).

To mark a string for translation in the Jinja2 and Django template
engines, you can use the `_()` function in the templates like this:

```
{{ _("English text") }}
```

If a string contains both a literal string component and variables,
you can use a block translation, which makes use of placeholders to
help translators to translate an entire sentence.  To translate a
block, Jinja2 uses the [trans][] tag while Django uses the
[blocktrans][] tag.  So rather than writing something ugly and
confusing for translators like this:

```
# Don't do this!
{{ _("This string will have") }} {{ value }} {{ _("inside") }}
```

You can instead use:

```
# Jinja2 style
{% trans %}This string will have {{ value }} inside.{% endtrans %}
# Django style
{% blocktrans %}This string will have {{ value }} inside.{% endblocktrans %}
```

Zulip expects all the error messages to be translatable as well.  To
ensure this, the error message passed to `json_error` and `JsonableError`
should always be a literal string enclosed by `_()` function, e.g:

```
json_error(_('English Text'))
JsonableError(_('English Text'))
```

To ensure we always internationalize our JSON errors messages, the
Zulip linter (`tools/lint-all`) checks for correct usage.

## Frontend Translations

Zulip uses the [i18next][] library for frontend translations. There
are two types of files in Zulip frontend which can hold translatable
strings, JavaScript code files and Handlebar templates. To mark a
string translatable in JavaScript files pass it to the `i18n.t` function.

```
i18n.t('English Text', context);
i18n.t('English text with a __variable__', {'variable': 'Variable value'});
```

Note: In the second example above, instead of enclosing the variable with
handlebars, `{{ }}`, we enclose it with `__` because we need to
differentiate the variable from the Handlebar tags. The symbol which is
used to enclose the variables can be changed in `/static/js/src/main.js`.

`i18next` also supports plural translations. To support plurals make
sure your resource file contatins the related keys:

```
{
    "en": {
        "translation": {
            "key": "item",
            "key_plural": "items",
            "keyWithCount": "__count__ item",
            "keyWithCount_plural": "__count__ items"
        }
    }
}
```

With this resource you can show plurals like this:

```
i18n.t('key', {count: 0}); // output: 'items'
i18n.t('key', {count: 1}); // output: 'item'
i18n.t('key', {count: 5}); // output: 'items'
i18n.t('key', {count: 100}); // output: 'items'
i18n.t('keyWithCount', {count: 0}); // output: '0 items'
i18n.t('keyWithCount', {count: 1}); // output: '1 item'
i18n.t('keyWithCount', {count: 5}); // output: '5 items'
i18n.t('keyWithCount', {count: 100}); // output: '100 items'
```

For further reading on plurals, read the [official] documentation.

To mark the strings as translatable in the Handlebar templates, Zulip
registers two Handlebar [helpers][]. The syntax for simple strings is:

```
{{t 'English Text' }}
```

The syntax for block strings or strings containing variables is:

```
{{tr context}}
    Block of English text.
{{/tr}}

var context = {'variable': 'variable value'};
{{tr context}}
    Block of English text with a __variable__.
{{/tr}}
```

The rules for plurals are same as for JavaScript files. You just have
to declare the appropriate keys in the resource file and then include the
`count` in the context.


[Django]: https://docs.djangoproject.com/en/1.9/topics/templates/#the-django-template-language
[Jinja2]: http://jinja.pocoo.org/
[Handlebars]: http://handlebarsjs.com/
[trans]: http://jinja.pocoo.org/docs/dev/templates/#i18n
[blocktrans]: https://docs.djangoproject.com/en/1.8/topics/i18n/translation/#std:templatetag-blocktrans
[i18next]: http://i18next.com
[official]: http://i18next.com/translate/pluralSimple/
[helpers]: http://handlebarsjs.com/block_helpers.html
[resource]: http://i18next.com/translate/

## Testing Translations

First of all make sure that you have compiled the translation strings
using `python manage.py compilemessages`.

Django figures out the effective language by going through the
following steps:

1. It looks for the language code in the url.
2. It looks for the LANGUGE_SESSION_KEY key in the current user's
session.
3. It looks for the cookie named 'django_language'. You can set a
different name through LANGUAGE_COOKIE_NAME setting.
4. It looks for the `Accept-Language` HTTP header in the HTTP request.
Normally your browser will take care of this.

The easiest way to test translations is through the i18n urls e.g. if
you have German translations available you can access the German
version of a page by going to `/de/path_to_page`.

To test translations using other methods you will need an HTTP client
library like `requests`, `cURL` or `urllib`. Here is a sample code to
test `Accept-Language` header using requests:

```
import requests
headers = {"Accept-Language": "de"}
response = requests.get("http://localhost:9991/login/", headers=headers)
print(response.content)
```