diff --git a/404.md b/404.md
index eac009baab..b673b732a9 100644
--- a/404.md
+++ b/404.md
@@ -8,15 +8,20 @@ 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';
+  // A language without its own 404 page is served this page again there
+  if (path === notFound) return;
+  // 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>