i18n: Pass language name with every response.

With a comment added by tabbott on live-update considerations.

See https://chat.zulip.org/#narrow/stream/9-issues/topic/FormatJS.20error.20in.20standalone.20pages/near/1168413 for context.

Signed-off-by: Anders Kaseorg <anders@zulip.com>

static/js/i18n.js

@@ -9,7 +9,7 @@ import {page_params} from "./page_params";
 const cache = createIntlCache();
 export const intl = createIntl(
     {
-        locale: page_params.default_language,
+        locale: page_params.request_language,
         defaultLocale: "en",
         messages: page_params.translation_data,
         onError: /* istanbul ignore next */ (error) => {

static/js/server_events_dispatch.js

@@ -573,6 +573,11 @@ export function dispatch_normal_event(event) {
             }
             if (event.setting_name === "default_language") {
                 // We additionally need to set the language name.
+                //
+                // Note that this does not change translations at all;
+                // a reload is fundamentally required because we
+                // cannot rerender with the new language the strings
+                // present in the backend/Jinja2 templates.
                 page_params.default_language_name = event.language_name;
             }
             if (event.setting_name === "twenty_four_hour_time") {

zerver/context_processors.py

@@ -2,9 +2,11 @@ from typing import Any, Dict, Optional
 from urllib.parse import urljoin
 
 from django.conf import settings
+from django.contrib.staticfiles.storage import staticfiles_storage
 from django.http import HttpRequest
 from django.utils.html import escape
 from django.utils.safestring import SafeString
+from django.utils.translation import get_language
 
 from version import (
     LATEST_MAJOR_VERSION,
@@ -28,6 +30,11 @@ from zproject.backends import (
     require_email_format_usernames,
 )
 
+DEFAULT_PAGE_PARAMS = {
+    "debug_mode": settings.DEBUG,
+    "webpack_public_path": staticfiles_storage.url(settings.WEBPACK_BUNDLES),
+}
+
 
 def common_context(user: UserProfile) -> Dict[str, Any]:
     """Common context used for things like outgoing emails that don't
@@ -129,6 +136,11 @@ def zulip_default_context(request: HttpRequest) -> Dict[str, Any]:
     # get the same result.
     platform = get_client_name(request)
 
+    default_page_params = {
+        **DEFAULT_PAGE_PARAMS,
+        "request_language": get_language(),
+    }
+
     context = {
         "root_domain_landing_page": settings.ROOT_DOMAIN_LANDING_PAGE,
         "custom_logo_url": settings.CUSTOM_LOGO_URL,
@@ -161,6 +173,7 @@ def zulip_default_context(request: HttpRequest) -> Dict[str, Any]:
         "platform": platform,
         "allow_search_engine_indexing": allow_search_engine_indexing,
         "landing_page_navbar_message": settings.LANDING_PAGE_NAVBAR_MESSAGE,
+        "default_page_params": default_page_params,
     }
 
     context["OPEN_GRAPH_URL"] = f"{realm_uri}{request.path}"

zerver/tests/test_home.py

@@ -202,6 +202,7 @@ class HomeTest(ZulipTestCase):
         "realm_waiting_period_threshold",
         "realm_wildcard_mention_policy",
         "recent_private_conversations",
+        "request_language",
         "root_domain_uri",
         "save_stacktraces",
         "search_pills_enabled",

zproject/jinja2/__init__.py

@@ -1,6 +1,5 @@
 from typing import Any
 
-from django.conf import settings
 from django.contrib.staticfiles.storage import staticfiles_storage
 from django.template.defaultfilters import pluralize, slugify
 from django.urls import reverse
@@ -9,16 +8,17 @@ from django.utils.timesince import timesince
 from jinja2 import Environment
 from two_factor.templatetags.two_factor import device_action
 
+from zerver.context_processors import DEFAULT_PAGE_PARAMS
 from zerver.templatetags.app_filters import display_list, render_markdown_path, webpack_entry
 
 
 def environment(**options: Any) -> Environment:
     env = Environment(**options)
     env.globals.update(
-        default_page_params={
+        # default_page_params is provided here for responses where
-            "debug_mode": settings.DEBUG,
+        # zulip_default_context is not run, including the 404.html and
-            "webpack_public_path": staticfiles_storage.url(settings.WEBPACK_BUNDLES),
+        # 500.html error pages.
-        },
+        default_page_params=DEFAULT_PAGE_PARAMS,
         static=staticfiles_storage.url,
         url=reverse,
         render_markdown_path=render_markdown_path,