diff --git a/tools/build-docs.mjs b/tools/build-docs.mjs
index 4ee51e9ab..cada7c0e1 100644
--- a/tools/build-docs.mjs
+++ b/tools/build-docs.mjs
@@ -14,6 +14,7 @@ import fs from 'node:fs';
 import path from 'node:path';
 import { fileURLToPath } from 'node:url';
 import { getSiteUrl } from '../website/src/lib/site-url.mjs';
+import { translatedLocales } from '../website/src/lib/locales.mjs';
 
 // =============================================================================
 // Configuration
@@ -41,10 +42,6 @@ const LLM_EXCLUDE_PATTERNS = [
   // Note: Files/dirs starting with _ (like _STYLE_GUIDE.md, _archive/) are excluded in shouldExcludeFromLlm()
 ];
 
-// Non-root locales — their docs duplicate English content and should not appear in llms-full.txt.
-// Update this list when adding new i18n locales in website/astro.config.mjs.
-const LLM_EXCLUDE_LOCALES = ['zh-cn', 'fr'];
-
 // =============================================================================
 // Main Entry Point
 /**
@@ -293,7 +290,7 @@ function shouldExcludeFromLlm(filePath) {
   if (pathParts.some((part) => part.startsWith('_'))) return true;
 
   // Exclude non-root locale directories (translations duplicate English content)
-  if (LLM_EXCLUDE_LOCALES.some((locale) => filePath.startsWith(`${locale}/`) || filePath.startsWith(`${locale}${path.sep}`))) return true;
+  if (translatedLocales.some((locale) => filePath.startsWith(`${locale}/`) || filePath.startsWith(`${locale}${path.sep}`))) return true;
 
   // Check configured patterns
   return LLM_EXCLUDE_PATTERNS.some((pattern) => filePath.includes(pattern));
diff --git a/website/astro.config.mjs b/website/astro.config.mjs
index b0f44d492..9d7efd99e 100644
--- a/website/astro.config.mjs
+++ b/website/astro.config.mjs
@@ -5,6 +5,7 @@ import sitemap from '@astrojs/sitemap';
 import rehypeMarkdownLinks from './src/rehype-markdown-links.js';
 import rehypeBasePaths from './src/rehype-base-paths.js';
 import { getSiteUrl } from './src/lib/site-url.mjs';
+import { locales } from './src/lib/locales.mjs';
 
 const siteUrl = getSiteUrl();
 const urlParts = new URL(siteUrl);
@@ -45,22 +46,9 @@ export default defineConfig({
       title: 'BMAD Method',
       tagline: 'AI-driven agile development with specialized agents and workflows that scale from bug fixes to enterprise platforms.',
 
-      // i18n: English as root (no URL prefix), Chinese at /zh-cn/, French at /fr/
+      // i18n: locale config from shared module (website/src/lib/locales.mjs)
       defaultLocale: 'root',
-      locales: {
-        root: {
-          label: 'English',
-          lang: 'en',
-        },
-        'zh-cn': {
-          label: '简体中文',
-          lang: 'zh-CN',
-        },
-        fr: {
-          label: 'Français',
-          lang: 'fr-FR',
-        },
-      },
+      locales,
 
       logo: {
         light: './public/img/bmad-light.png',
diff --git a/website/src/lib/locales.mjs b/website/src/lib/locales.mjs
new file mode 100644
index 000000000..ef7e273e9
--- /dev/null
+++ b/website/src/lib/locales.mjs
@@ -0,0 +1,32 @@
+/**
+ * Shared i18n locale configuration.
+ *
+ * Single source of truth for locale definitions used by:
+ *   - website/astro.config.mjs  (Starlight i18n)
+ *   - tools/build-docs.mjs      (llms-full.txt locale exclusion)
+ *   - website/src/pages/404.astro (client-side locale redirect)
+ *
+ * The root locale (English) uses Starlight's 'root' key convention
+ * (no URL prefix). All other locales get a URL prefix matching their key.
+ */
+
+export const locales = {
+  root: {
+    label: 'English',
+    lang: 'en',
+  },
+  'zh-cn': {
+    label: '简体中文',
+    lang: 'zh-CN',
+  },
+  fr: {
+    label: 'Français',
+    lang: 'fr-FR',
+  },
+};
+
+/**
+ * Non-root locale keys (the URL prefixes for translated content).
+ * @type {string[]}
+ */
+export const translatedLocales = Object.keys(locales).filter((k) => k !== 'root');
diff --git a/website/src/pages/404.astro b/website/src/pages/404.astro
index 945411ec9..6ae826ab7 100644
--- a/website/src/pages/404.astro
+++ b/website/src/pages/404.astro
@@ -1,6 +1,7 @@
 ---
 import StarlightPage from '@astrojs/starlight/components/StarlightPage.astro';
 import { getEntry } from 'astro:content';
+import { translatedLocales } from '../lib/locales.mjs';
 
 const entry = await getEntry('docs', '404');
 const { Content } = await entry.render();
@@ -12,12 +13,11 @@ const { Content } = await entry.render();
 
 <!-- GitHub Pages serves this single 404.html for all paths.
      Redirect to the locale-specific 404 page when the URL has a locale prefix. -->
-<script is:inline>
+<script is:inline define:vars={{ translatedLocales }}>
   (function () {
-    var locales = ['zh-cn', 'fr'];
     var path = window.location.pathname;
-    for (var i = 0; i < locales.length; i++) {
-      var prefix = '/' + locales[i] + '/';
+    for (var i = 0; i < translatedLocales.length; i++) {
+      var prefix = '/' + translatedLocales[i] + '/';
       if (path.startsWith(prefix) && path !== prefix + '404/') {
         window.location.replace(prefix + '404/');
         return;