diff --git a/browser-extensions/CHANGELOG.md b/browser-extensions/CHANGELOG.md
index 2cc7b4a..941b431 100644
--- a/browser-extensions/CHANGELOG.md
+++ b/browser-extensions/CHANGELOG.md
@@ -6,6 +6,8 @@ All notable changes to the shrtnr browser extensions are documented in this file
 
 Repairs the extension in real browsers, adds the parity features a shortener extension is expected to have, and hardens permissions. No new permissions.
 
+- **Simplified Chinese.** The popup and the options page follow the browser's language, and Chinese joins English, Indonesian and Swedish so the extension's set matches the admin app's. A browser reporting `zh-TW` or `zh-HK` reads Simplified: the extension carries one Chinese table, and it has no picker to choose another.
+
 - **Every request works again.** The lockfile pinned `@oddbit/shrtnr` 1.1.0, which calls `fetch` with the client object as receiver. Browsers reject that with `Illegal invocation`, the SDK reported it as a network failure, and the popup and the connection test showed "Can't reach your shrtnr" for every deployment. Verified in Chromium: zero requests left the browser. The floor is now 1.2.1, which also restores the `X-Client` header so links show as created via the SDK.
 - **Custom slug** field in the popup. Adds the slug to the link just created, swaps the short URL, copies it, and re-targets the QR code at the new slug. 409 shows "already taken" inline; a slug that breaks the rule is rejected before any request.
 - **Recent** list of the last five links shortened from this browser, kept on the device in `chrome.storage.local`.
diff --git a/browser-extensions/README.md b/browser-extensions/README.md
index 29cd123..d976dfa 100644
--- a/browser-extensions/README.md
+++ b/browser-extensions/README.md
@@ -88,7 +88,7 @@ The test suite covers:
 - `storage.ts`: get / set / clear / onConfigChange semantics, normalization, validation rejections
 - `recent.ts`: ordering, dedupe by link id, size cap, malformed entries, missing or failing local storage area
 - `api.ts`: client construction, internal-page guard, error-status to category mapping (including 409), slug validation and add, QR fetch with and without a slug, connection test
-- `i18n`: translation lookup, fallback to en, placeholder interpolation, key parity across all three languages
+- `i18n`: translation lookup, fallback to en, placeholder interpolation, key parity across every supported language, browser-language detection including script variants
 - `Popup.tsx`: every state in the state machine (loading, not-configured, success, error categories, recovery actions, QR toggle caching, visible QR errors, custom slug flow, recent list)
 - `Options.tsx`: CTA banner visibility rule, connection test rendering including the create-only note, save flow with permission request and revocation of the previous origin
 
@@ -161,7 +161,7 @@ Before tagging, run through the checklist in [`RELEASE.md`](RELEASE.md).
 
 ## i18n
 
-Three languages, mirroring the admin app: English, Indonesian, Swedish. English is the source of truth and the fallback. Add a key to `src/i18n/en.ts` first; TypeScript will fail to compile until `id.ts` and `sv.ts` add the same key (the `Translations = typeof en` type is the contract).
+The same languages as the admin app. `src/i18n/index.ts` lists them in `SUPPORTED_LANGUAGES`, which is where a new one is registered: the table map beside it is typed over that list, so a language without a table fails the typecheck. The language is the browser's, read from `navigator.language` by its primary subtag; there is no picker in the extension. English is the source of truth and the fallback. Add a key to `src/i18n/en.ts` first; TypeScript fails to compile until every other table adds the same key (the `Translations = typeof en` type is the contract).
 
 ## Related
 
diff --git a/browser-extensions/RELEASE.md b/browser-extensions/RELEASE.md
index db35e98..bc18d61 100644
--- a/browser-extensions/RELEASE.md
+++ b/browser-extensions/RELEASE.md
@@ -52,11 +52,13 @@ Firefox 140 or newer (`strict_min_version`), so the data-collection declaration
 
 ## 4. Locale check
 
-Switch the OS or browser locale to Indonesian, then to Swedish. Reload the popup and options page.
+Switch the OS or browser locale to Indonesian, then Swedish, then Chinese (Simplified). Reload the popup and options page.
 
 - [ ] Both surfaces render translated strings.
+- [ ] The Chinese labels are not clipped: the popup and the options page are the narrowest surfaces the strings land on.
 - [ ] Placeholders (`{host}`, `{message}`) interpolate correctly in error messages.
 - [ ] Fall back to English when the OS locale is something else (e.g. German).
+- [ ] A Traditional Chinese locale (`zh-TW`) renders Simplified, which is the documented behavior: the extension carries one Chinese table.
 
 ## 5. Bump and tag
 
diff --git a/browser-extensions/src/i18n/index.ts b/browser-extensions/src/i18n/index.ts
index 752f49d..e2c90b8 100644
--- a/browser-extensions/src/i18n/index.ts
+++ b/browser-extensions/src/i18n/index.ts
@@ -4,21 +4,29 @@
 import en from "./en";
 import id from "./id";
 import sv from "./sv";
+import zh from "./zh";
 import type { TranslationKey, Translations } from "./types";
 
 export type { TranslationKey, Translations };
 export type TranslateFn = (key: TranslationKey, params?: Record<string, string | number>) => string;
 
 export const DEFAULT_LANGUAGE = "en";
-export const SUPPORTED_LANGUAGES = ["en", "id", "sv"] as const;
+export const SUPPORTED_LANGUAGES = ["en", "id", "sv", "zh"] as const;
 export type SupportedLanguage = (typeof SUPPORTED_LANGUAGES)[number];
 
-const translations: Record<SupportedLanguage, Translations> = { en, id, sv };
+const translations: Record<SupportedLanguage, Translations> = { en, id, sv, zh };
 
 export function isSupportedLanguage(lang: string): lang is SupportedLanguage {
   return (SUPPORTED_LANGUAGES as readonly string[]).includes(lang);
 }
 
+/**
+ * The browser's language decides, by its primary subtag: "zh-CN", "zh-SG" and
+ * "zh-Hans" all resolve to "zh". A script variant this set does not carry,
+ * "zh-TW" or "zh-HK", also resolves to "zh" and reads the Simplified table.
+ * A Traditional locale would need its own entry here and would have to be
+ * matched before the primary subtag is taken, which this does not do.
+ */
 export function detectLanguage(): SupportedLanguage {
   const raw = typeof navigator !== "undefined" ? (navigator.language || "en") : "en";
   const primary = raw.split("-")[0]?.toLowerCase() ?? "en";
diff --git a/browser-extensions/src/i18n/zh.ts b/browser-extensions/src/i18n/zh.ts
new file mode 100644
index 0000000..66e1935
--- /dev/null
+++ b/browser-extensions/src/i18n/zh.ts
@@ -0,0 +1,94 @@
+// Copyright 2026 Oddbit (https://oddbit.id)
+// SPDX-License-Identifier: Apache-2.0
+
+import type { Translations } from "./types";
+
+const zh: Translations = {
+  "_lang": "zh",
+
+  // Brand
+  "brand.name": "shrtnr",
+  "brand.tagline": "自托管短链接服务",
+
+  // Popup: generic
+  "popup.loading": "正在缩短...",
+  "popup.shortUrlLabel": "短链接",
+  "popup.copy": "复制",
+  "popup.copied": "已复制",
+  "popup.qrShow": "显示二维码",
+  "popup.qrHide": "隐藏二维码",
+  "popup.qrLoading": "正在生成二维码...",
+  "popup.qrAlt": "短链接的二维码",
+  "popup.slug.label": "自定义短码",
+  "popup.slug.placeholder": "wo-de-lianjie",
+  "popup.slug.add": "添加短码",
+  "popup.slug.adding": "正在添加...",
+  "popup.slug.help": "可选。只能使用字母、数字和连字符。添加后的短码会立即复制。",
+  "popup.recent.heading": "此浏览器的最近记录",
+  "popup.viewInAdmin": "在管理后台查看",
+  "popup.openSettings": "设置",
+  "popup.retry": "重试",
+
+  // Popup: not configured
+  "popup.notConfigured.heading": "设置 shrtnr",
+  "popup.notConfigured.body": "shrtnr 需要自托管。将此扩展指向你的服务器即可开始缩短链接。",
+
+  // Form
+  "form.baseUrl.label": "服务器地址",
+  "form.baseUrl.placeholder": "https://shrtnr.example.com",
+  "form.baseUrl.help": "部署 shrtnr Worker 的域名。",
+  "form.apiKey.label": "API 密钥",
+  "form.apiKey.placeholder": "sk_...",
+  "form.apiKey.help": "在管理后台的 API 密钥页面创建一个。",
+  "form.test": "测试连接",
+  "form.save": "保存",
+  "form.cancel": "取消",
+  "form.testing": "正在测试...",
+  "form.testOk": "已连接",
+  "form.testOkCreateOnly": "已连接。该密钥只能创建链接、不能读取链接，因此二维码需要具备读取权限的密钥。",
+  "form.saving": "正在保存...",
+  "form.saved": "已保存",
+
+  // CTA
+  "cta.heading": "还没有自己的 shrtnr？",
+  "cta.body": "在 Cloudflare 上一键部署免费实例。免费套餐，无需信用卡。",
+  "cta.button": "免费部署",
+
+  // Errors (visible to users)
+  "error.internalPage": "shrtnr 无法缩短浏览器内部页面。",
+  "error.unparseable": "无法读取此标签页的网址。",
+  "error.network": "无法连接 {host} 上的 shrtnr。请检查地址或网络。",
+  "error.unauthorized": "你的 API 密钥被拒绝。请在设置中更新。",
+  "error.forbidden": "该 API 密钥不允许创建链接。",
+  "error.notFound": "在 {host} 上找不到 shrtnr API。是不是域名写错了？",
+  "error.conflict": "该短码已被占用。换一个试试。",
+  "error.slugInvalid": "短码只能使用字母、数字和连字符，且不能以连字符开头或结尾。",
+  "error.qrForbidden": "该 API 密钥无法读取链接，因此无法获取二维码。请使用具备读取权限的密钥。",
+  "error.qrFailed": "无法获取二维码。请重试。",
+  "error.rateLimited": "请求过于频繁。请稍后重试。",
+  "error.server": "你的 shrtnr 服务器返回了错误。",
+  "error.validation": "{message}",
+  "error.invalidUrl": "这不是有效的网址。请使用完整地址，例如 https://shrtnr.example.com。",
+  "error.saveFailed": "无法保存设置。请重试。",
+  "error.clipboard": "复制失败。请选中上方链接手动复制。",
+  "error.permissionDenied": "shrtnr 需要访问 {host} 的权限。请再次点击保存并允许。",
+  "error.permissionDeniedTest": "shrtnr 需要访问 {host} 的权限。请再次点击测试并允许。",
+
+  // Options page
+  "options.title": "shrtnr 设置",
+  "options.subtitle": "将此扩展连接到你的 shrtnr 部署。",
+  "options.section.connection": "连接",
+  "options.section.connection.body": "这些值保存在浏览器的同步设置中，绝不会发送给 Oddbit。",
+  "options.section.connection.scope": "只有创建权限的密钥就足以缩短链接。需要二维码时再加上读取权限。",
+  "options.section.shortcut": "键盘快捷键",
+  "options.section.shortcut.body": "{shortcut} 会打开弹窗并缩短当前标签页。可在浏览器的扩展快捷键页面修改。",
+  "options.section.shortcut.unassigned": "尚未分配快捷键。建议的组合可能已被其他扩展占用。请在浏览器的扩展快捷键页面分配。",
+  "options.section.about": "关于",
+  "options.section.about.body": "shrtnr 是开源且自托管的项目。源码：github.com/oddbit/shrtnr。",
+  "options.section.about.website": "oddbit.id",
+  "options.section.about.version": "版本 {version}",
+
+  // Footer
+};
+
+export default zh;
diff --git a/browser-extensions/tests/i18n.test.ts b/browser-extensions/tests/i18n.test.ts
index 73dcd46..3d69fa3 100644
--- a/browser-extensions/tests/i18n.test.ts
+++ b/browser-extensions/tests/i18n.test.ts
@@ -3,8 +3,6 @@
 
 import { describe, it, expect } from "vitest";
 import en from "../src/i18n/en";
-import id from "../src/i18n/id";
-import sv from "../src/i18n/sv";
 import {
   createTranslateFn,
   detectLanguage,
@@ -14,6 +12,18 @@ import {
   DEFAULT_LANGUAGE,
 } from "../src/i18n";
 
+/**
+ * Every supported language except the fallback, derived once here: the key
+ * and placeholder parity suites both iterate it, so a change to the default
+ * language or to the exclusion rule lands in one place.
+ */
+const translated = SUPPORTED_LANGUAGES.filter((lang) => lang !== DEFAULT_LANGUAGE);
+
+/** Sets navigator.language for one case. The global beforeEach re-pins it. */
+function browserLanguage(language: string): void {
+  Object.defineProperty(globalThis.navigator, "language", { configurable: true, value: language });
+}
+
 describe("i18n.createTranslateFn", () => {
   it("returns en strings for en", () => {
     const t = createTranslateFn("en");
@@ -31,6 +41,12 @@ describe("i18n.createTranslateFn", () => {
     expect(t("popup.copy")).toBe("Kopiera");
   });
 
+  it("returns zh strings for zh", () => {
+    // "复制" only comes from the zh table: a fallback would render "Copy".
+    const t = createTranslateFn("zh");
+    expect(t("popup.copy")).toBe("复制");
+  });
+
   it("falls back to en for unknown languages", () => {
     const t = createTranslateFn("xx");
     expect(t("popup.copy")).toBe("Copy");
@@ -46,24 +62,22 @@ describe("i18n.createTranslateFn", () => {
     expect(t("error.validation", { message: "URL too long" })).toBe("URL too long");
   });
 
-  it("localizes the invalid-URL error instead of passing English through", () => {
-    // error.validation is a "{message}" passthrough for server-supplied text.
-    // A client-side URL parse failure must carry its own localized key.
-    const enText = createTranslateFn("en")("error.invalidUrl");
-    const idText = createTranslateFn("id")("error.invalidUrl");
-    const svText = createTranslateFn("sv")("error.invalidUrl");
-    expect(enText).not.toBe("error.invalidUrl");
-    expect(idText).not.toBe(enText);
-    expect(svText).not.toBe(enText);
-  });
+  it.each(SUPPORTED_LANGUAGES)(
+    "localizes the invalid-URL error instead of passing English through (%s)",
+    (lang) => {
+      // error.validation is a "{message}" passthrough for server-supplied
+      // text. A client-side URL parse failure must carry its own localized
+      // key, in every language the extension offers.
+      const text = createTranslateFn(lang)("error.invalidUrl");
+      expect(text).not.toBe("error.invalidUrl");
+      if (lang !== DEFAULT_LANGUAGE) expect(text).not.toBe(en["error.invalidUrl"]);
+    },
+  );
 
-  it("localizes the save-failure message", () => {
-    const enText = createTranslateFn("en")("error.saveFailed");
-    const idText = createTranslateFn("id")("error.saveFailed");
-    const svText = createTranslateFn("sv")("error.saveFailed");
-    expect(enText).not.toBe("error.saveFailed");
-    expect(idText).not.toBe(enText);
-    expect(svText).not.toBe(enText);
+  it.each(SUPPORTED_LANGUAGES)("localizes the save-failure message (%s)", (lang) => {
+    const text = createTranslateFn(lang)("error.saveFailed");
+    expect(text).not.toBe("error.saveFailed");
+    if (lang !== DEFAULT_LANGUAGE) expect(text).not.toBe(en["error.saveFailed"]);
   });
 
   it("returns the key itself when missing in both target and fallback", () => {
@@ -74,29 +88,21 @@ describe("i18n.createTranslateFn", () => {
 });
 
 describe("i18n key parity", () => {
-  it("every en key exists in id", () => {
-    const enKeys = Object.keys(en);
-    const idKeys = new Set(Object.keys(id));
-    const missing = enKeys.filter((k) => !idKeys.has(k));
-    expect(missing).toEqual([]);
-  });
+  const enKeys = new Set(Object.keys(en));
 
-  it("every en key exists in sv", () => {
-    const enKeys = Object.keys(en);
-    const svKeys = new Set(Object.keys(sv));
-    const missing = enKeys.filter((k) => !svKeys.has(k));
-    expect(missing).toEqual([]);
+  it.each(translated)("locale %s carries every key en declares", (lang) => {
+    const keys = new Set(Object.keys(getTranslations(lang)));
+    expect([...enKeys].filter((k) => !keys.has(k))).toEqual([]);
   });
 
-  it("id and sv have no extra keys beyond en", () => {
-    const enKeys = new Set(Object.keys(en));
-    expect(Object.keys(id).filter((k) => !enKeys.has(k))).toEqual([]);
-    expect(Object.keys(sv).filter((k) => !enKeys.has(k))).toEqual([]);
+  it.each(translated)("locale %s carries no key beyond en", (lang) => {
+    const keys = new Set(Object.keys(getTranslations(lang)));
+    expect([...keys].filter((k) => !enKeys.has(k))).toEqual([]);
   });
 
   it("every value is a non-empty string in every language", () => {
-    for (const [lang, table] of Object.entries({ en, id, sv })) {
-      for (const [key, value] of Object.entries(table)) {
+    for (const lang of SUPPORTED_LANGUAGES) {
+      for (const [key, value] of Object.entries(getTranslations(lang))) {
         expect(typeof value, `${lang}.${key} must be a string`).toBe("string");
         expect(String(value).trim(), `${lang}.${key} must be non-empty`).not.toBe("");
       }
@@ -106,14 +112,21 @@ describe("i18n key parity", () => {
   it("placeholders match between en and translated languages", () => {
     const placeholderRe = /\{[^}]+\}/g;
     for (const key of Object.keys(en) as Array<keyof typeof en>) {
-      const enValue = en[key];
-      const idValue = id[key];
-      const svValue = sv[key];
-      const enPlaceholders = (enValue.match(placeholderRe) ?? []).sort();
-      const idPlaceholders = (idValue.match(placeholderRe) ?? []).sort();
-      const svPlaceholders = (svValue.match(placeholderRe) ?? []).sort();
-      expect(idPlaceholders, `id.${key} placeholders must match en`).toEqual(enPlaceholders);
-      expect(svPlaceholders, `sv.${key} placeholders must match en`).toEqual(enPlaceholders);
+      const enPlaceholders = (en[key].match(placeholderRe) ?? []).sort();
+      for (const lang of translated) {
+        const value = getTranslations(lang)[key];
+        expect(
+          (value.match(placeholderRe) ?? []).sort(),
+          `${lang}.${key} placeholders must match en`,
+        ).toEqual(enPlaceholders);
+      }
+    }
+  });
+
+  it("every table declares its own code in _lang", () => {
+    // Catches a table that was copied from another locale and never renamed.
+    for (const lang of SUPPORTED_LANGUAGES) {
+      expect(getTranslations(lang)["_lang"], lang).toBe(lang);
     }
   });
 });
@@ -123,18 +136,58 @@ describe("i18n.detectLanguage", () => {
     const detected = detectLanguage();
     expect(SUPPORTED_LANGUAGES).toContain(detected);
   });
+
+  it("reads a regional variant by its primary subtag", () => {
+    for (const [reported, expected] of [
+      ["en-GB", "en"],
+      ["id-ID", "id"],
+      ["sv-SE", "sv"],
+      ["zh-CN", "zh"],
+      ["zh-SG", "zh"],
+      ["ZH-cn", "zh"],
+    ] as const) {
+      browserLanguage(reported);
+      expect(detectLanguage(), reported).toBe(expected);
+    }
+  });
+
+  it("resolves a Chinese script variant to Simplified", () => {
+    // The extension carries one Chinese table, so a Traditional reader gets
+    // Simplified rather than English. Pinned so the choice is deliberate:
+    // a zh-Hant table would have to be matched before the primary subtag is
+    // taken, which detectLanguage() does not do today.
+    for (const reported of ["zh-TW", "zh-HK", "zh-Hant"]) {
+      browserLanguage(reported);
+      expect(detectLanguage(), reported).toBe("zh");
+    }
+  });
+
+  it("falls back to English for a language the extension does not carry", () => {
+    for (const reported of ["fr-FR", "de", "ja-JP", ""]) {
+      browserLanguage(reported);
+      expect(detectLanguage(), `reported ${JSON.stringify(reported)}`).toBe(DEFAULT_LANGUAGE);
+    }
+  });
 });
 
 describe("i18n.isSupportedLanguage", () => {
-  it("accepts en, id, sv", () => {
-    expect(isSupportedLanguage("en")).toBe(true);
-    expect(isSupportedLanguage("id")).toBe(true);
-    expect(isSupportedLanguage("sv")).toBe(true);
+  it("accepts every supported language", () => {
+    for (const lang of SUPPORTED_LANGUAGES) {
+      expect(isSupportedLanguage(lang), lang).toBe(true);
+    }
+  });
+
+  it("carries exactly the languages it declares", () => {
+    expect([...SUPPORTED_LANGUAGES]).toEqual(["en", "id", "sv", "zh"]);
   });
+
   it("rejects everything else", () => {
     expect(isSupportedLanguage("fr")).toBe(false);
     expect(isSupportedLanguage("")).toBe(false);
     expect(isSupportedLanguage("EN")).toBe(false);
+    // A regional variant is not a language code of its own: detectLanguage()
+    // reduces it to the primary subtag before asking.
+    expect(isSupportedLanguage("zh-CN")).toBe(false);
   });
 });
 
@@ -142,8 +195,10 @@ describe("i18n.getTranslations", () => {
   it("returns en for unknown lang", () => {
     expect(getTranslations("xx")).toBe(en);
   });
-  it("returns id for id", () => {
-    expect(getTranslations("id")).toBe(id);
+  it("returns the table the language names", () => {
+    for (const lang of SUPPORTED_LANGUAGES) {
+      expect(getTranslations(lang)["_lang"], lang).toBe(lang);
+    }
   });
   it("DEFAULT_LANGUAGE is en", () => {
     expect(DEFAULT_LANGUAGE).toBe("en");
diff --git a/browser-extensions/tests/popup.test.tsx b/browser-extensions/tests/popup.test.tsx
index 1bee1a5..3d80b9d 100644
--- a/browser-extensions/tests/popup.test.tsx
+++ b/browser-extensions/tests/popup.test.tsx
@@ -48,6 +48,19 @@ describe("Popup — not configured", () => {
       expect(link.href).toContain("oddb.it/shrtnr-deploy-ext");
     });
   });
+
+  it("renders in Simplified Chinese when the browser reports zh-CN", async () => {
+    // The language comes from the browser, with no picker in the extension, so
+    // this is the whole path from navigator.language to the strings on screen.
+    // Every other case in this file runs against the en-US pin in setup.ts.
+    Object.defineProperty(globalThis.navigator, "language", { configurable: true, value: "zh-CN" });
+    await renderPopup();
+    await waitFor(() => {
+      expect(screen.getByRole("button", { name: "保存" })).toBeTruthy();
+    });
+    expect(screen.getByRole("button", { name: "测试连接" })).toBeTruthy();
+    expect(screen.queryByRole("button", { name: /save/i })).toBeNull();
+  });
 });
 
 describe("Popup — success", () => {