> Supporting internationalization is not optional. It must be a core feature.
>
> — [Jannis Leidel, speaking at Django Under the Hood, 2015][cite].
REST framework ships with translatable error messages. You can make these appear in your language enabling [Django's standard translation mechanisms][django-translation].
Doing so will allow you to:
* Select a language other than English as the default, using the standard `LANGUAGE_CODE` Django setting.
* Allow clients to choose a language themselves, using the `LocaleMiddleware` included with Django. A typical usage for API clients would be to include an `Accept-Language` request header.
When per-request internationalization is enabled, client requests will respect the `Accept-Language` header where possible. For example, let's make a request for an unsupported media type:
**Request**
GET /api/users HTTP/1.1
Accept: application/xml
Accept-Language: es-es
Host: example.org
**Response**
HTTP/1.0 406 NOT ACCEPTABLE
{"detail": "No se ha podido satisfacer la solicitud de cabecera de Accept."}
REST framework includes these built-in translations both for standard exception cases, and for serializer validation errors.
Note that the translations only apply to the error strings themselves. The format of error messages, and the keys of field names will remain the same. An example `400 Bad Request` response body might look like this:
If you want to use different string for parts of the response such as `detail` and `non_field_errors` then you can modify this behavior by using a [custom exception handler][custom-exception-handler].
* Your project includes custom error messages, which are not part of REST framework's default translation strings.
#### Translating a new language locally
This guide assumes you are already familiar with how to translate a Django app. If you're not, start by reading [Django's translation docs][django-translation].
If you're translating a new language you'll need to translate the existing REST framework error messages:
1. Make a new folder where you want to store the internationalization resources. Add this path to your [`LOCALE_PATHS`][django-locale-paths] setting.
2. Now create a subfolder for the language you want to translate. The folder should be named using [locale name][django-locale-name] notation. For example: `de`, `pt_BR`, `es_AR`.
3. Now copy the [base translations file][django-po-source] from the REST framework source code into your translations folder.
4. Edit the `django.po` file you've just copied, translating all the error messages.
available for Django to use. You should see a message like `processing file django.po in <...>/locale/pt_BR/LC_MESSAGES`.
6. Restart your development server to see the changes take effect.
If you're only translating custom error messages that exist inside your project codebase you don't need to copy the REST framework source `django.po` file into a `LOCALE_PATHS` folder, and can instead simply run Django's standard `makemessages` process.
You can find more information on how the language preference is determined in the [Django documentation][django-language-preference]. For reference, the method is:
1. First, it looks for the language prefix in the requested URL.
2. Failing that, it looks for the `LANGUAGE_SESSION_KEY` key in the current user’s session.
3. Failing that, it looks for a cookie.
4. Failing that, it looks at the `Accept-Language` HTTP header.
5. Failing that, it uses the global `LANGUAGE_CODE` setting.
For API clients the most appropriate of these will typically be to use the `Accept-Language` header; Sessions and cookies will not be available unless using session authentication, and generally better practice to prefer an `Accept-Language` header for API clients rather than using language URL prefixes.
