# documentación de Django - 1.10.7

# Código fuente para django.middleware.locale

    "This is the locale selecting middleware that will look at accept headers"

    from django.conf import settings
    from django.conf.urls.i18n import is_language_prefix_patterns_used
    from django.http import HttpResponseRedirect
    from django.urls import get_script_prefix, is_valid_path
    from django.utils import translation
    from django.utils.cache import patch_vary_headers
    from django.utils.deprecation import MiddlewareMixin

    class LocaleMiddleware(MiddlewareMixin):
        """
        This is a very simple middleware that parses a request
        and decides what translation object to install in the current
        thread context. This allows pages to be dynamically
        translated to the language the user desires (if the language
        is available, of course).
        """
        response_redirect_class = HttpResponseRedirect

        def process_request(self, request):
            urlconf = getattr(request, 'urlconf', settings.ROOT_URLCONF)
            i18n_patterns_used, prefixed_default_language = is_language_prefix_patterns_used(urlconf)
            language = translation.get_language_from_request(request, check_path=i18n_patterns_used)
            language_from_path = translation.get_language_from_path(request.path_info)
            if not language_from_path and i18n_patterns_used and not prefixed_default_language:
                language = settings.LANGUAGE_CODE
            translation.activate(language)
            request.LANGUAGE_CODE = translation.get_language()

        def process_response(self, request, response):
            language = translation.get_language()
            language_from_path = translation.get_language_from_path(request.path_info)
            urlconf = getattr(request, 'urlconf', settings.ROOT_URLCONF)
            i18n_patterns_used, prefixed_default_language = is_language_prefix_patterns_used(urlconf)

            if (response.status_code == 404 and not language_from_path and
                    i18n_patterns_used and prefixed_default_language):
                # Maybe the language code is missing in the URL? Try adding the
                # language prefix and redirecting to that URL.
                language_path = '/%s%s' % (language, request.path_info)
                path_valid = is_valid_path(language_path, urlconf)
                path_needs_slash = (
                    not path_valid and (
                        settings.APPEND_SLASH and not language_path.endswith('/') and
                        is_valid_path('%s/' % language_path, urlconf)
                    )
                )

                if path_valid or path_needs_slash:
                    script_prefix = get_script_prefix()
                    # Insert language after the script prefix and before the
                    # rest of the URL
                    language_url = request.get_full_path(force_append_slash=path_needs_slash).replace(
                        script_prefix,
                        '%s%s/' % (script_prefix, language),
                        1
                    )
                    return self.response_redirect_class(language_url)

            if not (i18n_patterns_used and language_from_path):
                patch_vary_headers(response, ('Accept-Language',))
            if 'Content-Language' not in response:
                response['Content-Language'] = language
            return response