SEO fix for Django 1.4 LocaleMiddleware based on this article: http://blog.yawd.eu/2012/impact-django-page-redirects-seo/

middleware.py

from django.conf import settings
from django.core.urlresolvers import is_valid_path
from django.http import HttpResponsePermanentRedirect
from django.middleware.locale import LocaleMiddleware
from django.utils import translation
from django.utils.cache import patch_vary_headers

class UpdatedLocaleMiddleware(LocaleMiddleware):
    
    def process_response(self, request, response):
        language = translation.get_language()
        if (response.status_code == 404 and
                not translation.get_language_from_path(request.path_info)
                    and self.is_language_prefix_patterns_used()):
            urlconf = getattr(request, 'urlconf', None)
            language_path = '/%s%s' % (language, request.path_info)
            if settings.APPEND_SLASH and not language_path.endswith('/'):
                language_path = language_path + '/'

            if is_valid_path(language_path, urlconf):
                language_url = "%s://%s/%s%s" % (
                    request.is_secure() and 'https' or 'http',
                    request.get_host(), language, request.get_full_path())
                return HttpResponsePermanentRedirect(language_url)
        translation.deactivate()

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