# Django 5.2 documentation

# Source code for django.middleware.locale

    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):
        """
        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).
        """

        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)
                    # Redirect to the language-specific URL as detected by
                    # get_language_from_request(). HTTP caches may cache this
                    # redirect, so add the Vary header.
                    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