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>

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={
-            "debug_mode": settings.DEBUG,
-            "webpack_public_path": staticfiles_storage.url(settings.WEBPACK_BUNDLES),
-        },
+        # default_page_params is provided here for responses where
+        # zulip_default_context is not run, including the 404.html and
+        # 500.html error pages.
+        default_page_params=DEFAULT_PAGE_PARAMS,
         static=staticfiles_storage.url,
         url=reverse,
         render_markdown_path=render_markdown_path,