diff --git a/bin/build-pages.d.mts b/bin/build-pages.d.mts
index afaec7b4..f03ee374 100644
--- a/bin/build-pages.d.mts
+++ b/bin/build-pages.d.mts
@@ -10,7 +10,10 @@ export interface GeneratedPage {
    */
   kind: 'home' | 'landing' | 'doc';
 }
-export const LOCALES: Record<string, { prefix: string; lang: string; label: string; home: string; dir: string }>;
+export const LOCALES: Record<
+  string,
+  { prefix: string; lang: string; label: string; home: string; dir: string; og: string }
+>;
 export const LANDING_SLUGS: string[];
 export const PAGES: Array<{
   slug: string;
diff --git a/bin/build-pages.mjs b/bin/build-pages.mjs
index 5b29acca..fe1d2981 100644
--- a/bin/build-pages.mjs
+++ b/bin/build-pages.mjs
@@ -34,13 +34,15 @@ const REPO = 'https://github.com/ranuts/document';
 
 /** Locales the shell knows about. `prefix` is the URL directory; '' = root. */
 export const LOCALES = {
-  en: { prefix: '', lang: 'en', label: 'EN', home: '/', dir: 'ltr' },
-  'zh-CN': { prefix: '/zh-CN', lang: 'zh-CN', label: '中文', home: '/zh-CN/', dir: 'ltr' },
-  ja: { prefix: '/ja', lang: 'ja', label: '日本語', home: '/ja/', dir: 'ltr' },
-  de: { prefix: '/de', lang: 'de', label: 'Deutsch', home: '/de/', dir: 'ltr' },
-  es: { prefix: '/es', lang: 'es', label: 'Español', home: '/es/', dir: 'ltr' },
-  ko: { prefix: '/ko', lang: 'ko', label: '한국어', home: '/ko/', dir: 'ltr' },
-  pt: { prefix: '/pt', lang: 'pt', label: 'Português', home: '/pt/', dir: 'ltr' },
+  en: { prefix: '', lang: 'en', label: 'EN', home: '/', dir: 'ltr', og: 'en_US' },
+  'zh-CN': { prefix: '/zh-CN', lang: 'zh-CN', label: '中文', home: '/zh-CN/', dir: 'ltr', og: 'zh_CN' },
+  ja: { prefix: '/ja', lang: 'ja', label: '日本語', home: '/ja/', dir: 'ltr', og: 'ja_JP' },
+  de: { prefix: '/de', lang: 'de', label: 'Deutsch', home: '/de/', dir: 'ltr', og: 'de_DE' },
+  es: { prefix: '/es', lang: 'es', label: 'Español', home: '/es/', dir: 'ltr', og: 'es_ES' },
+  ko: { prefix: '/ko', lang: 'ko', label: '한국어', home: '/ko/', dir: 'ltr', og: 'ko_KR' },
+  // pt_BR, not pt_PT: the pages, the shell strings and the vendor locale the
+  // editor loads (pt.json) are all Brazilian Portuguese.
+  pt: { prefix: '/pt', lang: 'pt', label: 'Português', home: '/pt/', dir: 'ltr', og: 'pt_BR' },
 };
 const DEFAULT_LOCALE = 'en';
 
@@ -614,6 +616,10 @@ function renderHome({ locale, data, locales }) {
   const alternates = locales
     .map((l) => `    <link rel="alternate" hreflang="${l}" href="${ORIGIN + LOCALES[l].home}" />`)
     .join('\n');
+  const ogAlternates = locales
+    .filter((l) => l !== locale)
+    .map((l) => `    <meta property="og:locale:alternate" content="${LOCALES[l].og}" />`)
+    .join('\n');
   const langOptions = locales
     .map((l) => `            <r-option value="${l}" data-href="${LOCALES[l].home}">${LOCALES[l].label}</r-option>`)
     .join('\n');
@@ -751,6 +757,8 @@ ${alternates}
 
     <meta property="og:type" content="website" />
     <meta property="og:site_name" content="Online Document Editor" />
+    <meta property="og:locale" content="${L.og}" />
+${ogAlternates}
     <meta property="og:title" content="${e(data.title)}" />
     <meta property="og:description" content="${e(data.ogDescription || data.description)}" />
     <meta property="og:url" content="${url}" />
@@ -959,6 +967,7 @@ function renderPage({ page, locale, meta, body, headings, faq, steps, source })
           applicationCategory: 'BusinessApplication',
           operatingSystem: 'Any (web browser)',
           isAccessibleForFree: true,
+          inLanguage: L.lang,
           description: meta.appDescription || description,
           offers: { '@type': 'Offer', price: '0', priceCurrency: 'USD' },
         }
@@ -1006,10 +1015,17 @@ function renderPage({ page, locale, meta, body, headings, faq, steps, source })
   crumbs.push({ '@type': 'ListItem', position: crumbs.length + 1, name: meta.breadcrumb || title, item: url });
   graph.push({ '@type': 'BreadcrumbList', itemListElement: crumbs });
 
-  const alternates = Object.keys(LOCALES)
-    .filter((l) => page.sources[l])
+  const translations = Object.keys(LOCALES).filter((l) => page.sources[l]);
+  const alternates = translations
     .map((l) => `    <link rel="alternate" hreflang="${l}" href="${ORIGIN + routeFor(l, page.slug)}" />`)
     .join('\n');
+  // Open Graph carries the same set as hreflang, in its own spelling: the
+  // language of this page, then the others it exists in. Without it a share of
+  // /ja/ or /pt/ is treated as English by every consumer that reads OG.
+  const ogAlternates = translations
+    .filter((l) => l !== locale)
+    .map((l) => `    <meta property="og:locale:alternate" content="${LOCALES[l].og}" />`)
+    .join('\n');
   const langOptions = Object.keys(LOCALES)
     .filter((l) => page.sources[l])
     .map(
@@ -1095,6 +1111,8 @@ ${alternates}
 
     <meta property="og:type" content="${isLanding ? 'website' : 'article'}" />
     <meta property="og:site_name" content="Online Document Editor" />
+    <meta property="og:locale" content="${L.og}" />
+${ogAlternates}
     <meta property="og:title" content="${escapeHtml(title)}" />
     <meta property="og:description" content="${escapeHtml(cardDescription)}" />
     <meta property="og:url" content="${url}" />
diff --git a/docs/explorations/2026-08-23-seven-languages-audit.md b/docs/explorations/2026-08-23-seven-languages-audit.md
index 73c20b77..0e78cbbe 100644
--- a/docs/explorations/2026-08-23-seven-languages-audit.md
+++ b/docs/explorations/2026-08-23-seven-languages-audit.md
@@ -50,6 +50,19 @@ landing.css。白色主题下看不出来，暗色下就是页面四周一圈底
 它遍历 `public/` 下所有 HTML，七种语言进来之后从 97 KB 涨到 680 KB——同样的事实说七遍。
 对读它的模型只有害处。改成只收英文页面，开头说明镜像在哪；`/llms.txt` 仍然逐语言列出。
 
+## 8. Open Graph 不知道站点有七种语言（已修）
+
+`hreflang` 是完整的七语言互指，但 Open Graph 那边**一个字都没说**：既没有 `og:locale`
+也没有 `og:locale:alternate`。后果是任何读 OG 的消费者（Facebook、LinkedIn、Slack、
+各类抓取器）把 `/ja/` 和 `/pt/` 的分享都当成英文页。补上之后每页声明自己的
+`og:locale`，并列出其余六种的 `og:locale:alternate`。
+
+映射写在 `LOCALES` 表里，因为 OG 要的是 `language_TERRITORY` 而不是 BCP47：
+`en_US` / `zh_CN` / `ja_JP` / `de_DE` / `es_ES` / `ko_KR` / **`pt_BR`**。最后一个再次
+确认了第 6 条的取舍——页面、shell 词条、vendor 包（`pt.json`）、OG locale 四处都是巴西葡语。
+
+顺带补上落地页 `WebApplication` 节点缺的 `inLanguage`（首页和文档页早就有）。
+
 ## 复查过但没有问题的
 
 - **SEO 覆盖**：7 种语言 × 21 页齐全；hreflang 是完整的七语言互指 + x-default；
@@ -60,6 +73,16 @@ landing.css。白色主题下看不出来，暗色下就是页面四周一圈底
 - **德语长词**：`Installieren und im Flugzeug nutzen`（35 字符）在 pillars 列里正常换行，
   没有溢出。
 - **`/embed-demo`**：仍然是英文，这是 CLAUDE.md 的规矩（共用页面用英文），不是遗漏。
+- **站内死链**：158 个页面、5043 条内链、165 个不同目标，逐个请求，零 4xx。
+- **基础可达性**：五类页面上没有缺 alt 的图、没有无名链接/按钮、标题层级不跳级、
+  每页恰好一个 h1、`<html lang>` 都在。格式索引的行、右栏链接、语言选择器都能 Tab 到。
+- **首屏性能**：落地页 10 个请求 / 392 KB，FCP 44 ms。首页看起来 9 MB 是
+  `landing-prefetch.js` 在预热三个编辑器引擎（既有行为，有 E2E 钉着），发生在
+  load 之后；线上走 br 压缩（`sdk-all.js` 13.7 MB → 3.0 MB）。
+- **缓存头**：`sdkjs/` 与 `web-apps/` 故意不上 `immutable`（里面有我们的补丁和
+  iframe HTML），4 小时 + `must-revalidate`。这次补齐的 locale JSON 也在这棵树里，
+  但 SW 的 runtime cache 按 `VENDOR_VERSION` 命名，vendor 一变就是新 cache，
+  拿不到旧副本。
 
 ## 还没做的
 
diff --git a/index.html b/index.html
index 11327aaf..5df1fa9b 100644
--- a/index.html
+++ b/index.html
@@ -57,6 +57,13 @@
 
     <meta property="og:type" content="website" />
     <meta property="og:site_name" content="Online Document Editor" />
+    <meta property="og:locale" content="en_US" />
+    <meta property="og:locale:alternate" content="zh_CN" />
+    <meta property="og:locale:alternate" content="ja_JP" />
+    <meta property="og:locale:alternate" content="de_DE" />
+    <meta property="og:locale:alternate" content="es_ES" />
+    <meta property="og:locale:alternate" content="ko_KR" />
+    <meta property="og:locale:alternate" content="pt_BR" />
     <meta property="og:title" content="Open DOCX, XLSX &amp; PPTX in Your Browser — Free Document Viewer &amp; Editor" />
     <meta property="og:description" content="Open, view and edit DOCX, XLSX, PPTX and CSV in your browser — no Office, no upload, no sign-up. Free and offline-capable." />
     <meta property="og:url" content="https://edit.chaxus.com/" />
diff --git a/test/unit/landing-pages.test.ts b/test/unit/landing-pages.test.ts
index e687f89e..98dec821 100644
--- a/test/unit/landing-pages.test.ts
+++ b/test/unit/landing-pages.test.ts
@@ -150,6 +150,22 @@ describe('landing pages', () => {
         }
       });
 
+      /**
+       * Open Graph has its own spelling of the same set hreflang carries. A
+       * share of /ja/ or /pt/ without og:locale is read as English by every
+       * consumer that looks at OG -- which is most of them.
+       */
+      it('declares its Open Graph locale, and the ones it is also published in', () => {
+        const og = (l: string) => LOCALES[l].og;
+        expect(attr(html, /property="og:locale" content="([^"]+)"/), `${route} og:locale`).toBe(og(locale));
+
+        const alternates = [...html.matchAll(/property="og:locale:alternate" content="([^"]+)"/g)].map((m) => m[1]);
+        const expected = Object.keys(LOCALES)
+          .filter((l) => l !== locale && routes.has(routeIn(l, enRoute)))
+          .map(og);
+        expect(alternates.sort(), `${route} og:locale:alternate`).toEqual(expected.sort());
+      });
+
       it('offers every translation it has in the language switch', () => {
         for (const other of Object.keys(LOCALES)) {
           const target = routeIn(other, enRoute);