parse a request and decide 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 maybe the language code is missing in the url try adding the language prefix and redirecting to that url insert language after the script prefix and before the rest of the url redirect to the languagespecific url as detected by getlanguagefromrequest http caches may cache this redirect so add the vary header parse a request and decide 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 maybe the language code is missing in the url try adding the language prefix and redirecting to that url insert language after the script prefix and before the rest of the url redirect to the language specific url as detected by get_language_from_request http caches may cache this redirect so add the vary header
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):
    

    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
        ):
            
            
            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()
                
                
                language_url = request.get_full_path(
                    force_append_slash=path_needs_slash
                ).replace(script_prefix, "%s%s/" % (script_prefix, language), 1)
                
                
                
                redirect = self.response_redirect_class(language_url)
                patch_vary_headers(redirect, ("Accept-Language", "Cookie"))
                return redirect

        if not (i18n_patterns_used and language_from_path):
            patch_vary_headers(response, ("Accept-Language",))
        response.headers.setdefault("Content-Language", language)
        return response