From 312abeab4ae61a24f24bed58f439de10b6916691 Mon Sep 17 00:00:00 2001
From: Hiroshi SHIBATA <hsbt@ruby-lang.org>
Date: Tue, 15 Sep 2026 13:22:10 +0900
Subject: [PATCH 1/3] Generate the 404 language list from site data

The hand-written list still had the old `ua` code, so a missing page
under /uk/ stayed on the English 404 page instead of /uk/404.html.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
---
 404.md | 15 ++++++---------
 1 file changed, 6 insertions(+), 9 deletions(-)

diff --git a/404.md b/404.md
index eac009baab..0796f992d0 100644
--- a/404.md
+++ b/404.md
@@ -8,15 +8,12 @@ sitemap: false
 
 <script>
 (function() {
-  // Detect language from URL path
-  var path = window.location.pathname;
-  var match = path.match(/^\/(bg|de|en|es|fr|id|it|ja|ko|pl|pt|ru|tr|ua|vi|zh_cn|zh_tw)\//);
-
-  if (match && match[1] !== 'en') {
-    var lang = match[1];
-    // Redirect to language-specific 404 page
-    window.location.href = '/' + lang + '/404.html';
-  }
+  const languages = {{ site.data.languages | map: "code" | jsonify }};
+  const path = window.location.pathname;
+  const match = path.match(/^\/([^\/]+)(\/.*)$/);
+  if (!match || match[1] === 'en' || !languages.includes(match[1])) return;
+  const notFound = '/' + match[1] + '/404.html';
+  window.location.href = notFound;
 })();
 </script>
 

From 50c142e92fdad6f9af8e00cf6b1a5ec435ec0b12 Mon Sep 17 00:00:00 2001
From: Hiroshi SHIBATA <hsbt@ruby-lang.org>
Date: Tue, 15 Sep 2026 13:22:27 +0900
Subject: [PATCH 2/3] Stop the 404 redirect loop for languages without a 404
 page

vi has no 404 page, so /vi/404.html is answered with the root 404 page,
whose script redirected to /vi/404.html again without end.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
---
 404.md | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/404.md b/404.md
index 0796f992d0..08ca341d4c 100644
--- a/404.md
+++ b/404.md
@@ -13,6 +13,8 @@ sitemap: false
   const match = path.match(/^\/([^\/]+)(\/.*)$/);
   if (!match || match[1] === 'en' || !languages.includes(match[1])) return;
   const notFound = '/' + match[1] + '/404.html';
+  // A language without its own 404 page is served this page again there
+  if (path === notFound) return;
   window.location.href = notFound;
 })();
 </script>

From 64ba76acad0301e381bdfc9ef908a962020de963 Mon Sep 17 00:00:00 2001
From: Hiroshi SHIBATA <hsbt@ruby-lang.org>
Date: Tue, 15 Sep 2026 13:22:39 +0900
Subject: [PATCH 3/3] Redirect missing translations to the English page

A page or news post that has not been translated returned the
language's 404 page, although the English original exists. GitHub
Pages serves the root 404 page for every missing URL, so check the
English URL from there instead of copying English pages into each
language.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
---
 404.md | 8 +++++++-
 1 file changed, 7 insertions(+), 1 deletion(-)

diff --git a/404.md b/404.md
index 08ca341d4c..b673b732a9 100644
--- a/404.md
+++ b/404.md
@@ -15,7 +15,13 @@ sitemap: false
   const notFound = '/' + match[1] + '/404.html';
   // A language without its own 404 page is served this page again there
   if (path === notFound) return;
-  window.location.href = notFound;
+  // Fall back to the English page when a translation does not exist
+  const english = '/en' + match[2];
+  fetch(english, { method: 'HEAD' })
+    .then(function(res) { return res.ok; }, function() { return false; })
+    .then(function(found) {
+      window.location.replace(found ? english + window.location.search + window.location.hash : notFound);
+    });
 })();
 </script>