diff --git a/docs/superpowers/plans/2026-07-11-browser-extension-localization.md b/docs/superpowers/plans/2026-07-11-browser-extension-localization.md
new file mode 100644
index 0000000..e4668cf
--- /dev/null
+++ b/docs/superpowers/plans/2026-07-11-browser-extension-localization.md
@@ -0,0 +1,328 @@
+# Browser Extension Localization Implementation Plan
+
+> **For agentic workers:** REQUIRED SUB-SKILL: Use superpowers:subagent-driven-development (recommended) or superpowers:executing-plans to implement this plan task-by-task. Steps use checkbox (`- [ ]`) syntax for tracking.
+
+**Goal:** Add persisted `System / English / Russian` language selection to the browser extension, localizing popup chrome and context menus in Chromium and Firefox.
+
+**Architecture:** A framework-independent `shared/i18n.js` resolves preferences and loads extension-owned JSON catalogs. Popup and background both consume it; background owns persistence and context-menu recreation, while popup performs immediate DOM translation and sends settings updates.
+
+**Tech Stack:** WebExtension APIs, plain ES5-compatible JavaScript, JSON catalogs, Node `assert`/`vm` tests, existing Node build script.
+
+## Global Constraints
+
+- Store only `system`, `en`, or `ru`; missing/invalid values normalize to `system`.
+- `ru` and `ru-*` browser UI locales resolve to Russian; all other system locales resolve to English.
+- Keep the extension language independent from desktop settings.
+- Add no runtime dependency and no manifest-localization scope.
+- Never translate receiver URLs, tokens, file names, user content, or raw receiver error text.
+- Preserve receiver URL/token values when language changes.
+- Both browser distributions must contain `i18n.js`, `locales/en.json`, and `locales/ru.json`.
+
+---
+
+### Task 1: Shared Locale Runtime and Catalog Contract
+
+**Files:**
+
+- Create: `shared/i18n.js`
+- Create: `shared/locales/en.json`
+- Create: `shared/locales/ru.json`
+- Create: `scripts/test-i18n.js`
+- Modify: `package.json`
+
+**Interfaces:**
+
+- Produces: `globalThis.VerstakBrowserI18n.normalizePreference(value)`.
+- Produces: `globalThis.VerstakBrowserI18n.resolveLocale(preference, systemLocale)`.
+- Produces: `globalThis.VerstakBrowserI18n.loadCatalogs(loadJSON)` returning `Promise<{en,ru}>`.
+- Produces: `globalThis.VerstakBrowserI18n.createTranslator(catalogs, locale)` returning `t(key, params, fallback)`.
+
+- [ ] **Step 1: Write the failing runtime/catalog test**
+
+Create `scripts/test-i18n.js` that loads `shared/i18n.js` in `vm`, reads both JSON catalogs, and asserts:
+
+```js
+assert.strictEqual(i18n.normalizePreference('de'), 'system');
+assert.strictEqual(i18n.resolveLocale('system', 'ru-RU'), 'ru');
+assert.strictEqual(i18n.resolveLocale('system', 'uk-UA'), 'en');
+assert.strictEqual(i18n.resolveLocale('en', 'ru-RU'), 'en');
+assert.deepStrictEqual(Object.keys(ru).sort(), Object.keys(en).sort());
+assert.ok(Object.values(en).every((value) => typeof value === 'string'));
+assert.ok(Object.values(ru).every((value) => typeof value === 'string'));
+assert.strictEqual(i18n.createTranslator({ en, ru }, 'ru')('status.queued'), 'В очереди до запуска Верстака');
+assert.strictEqual(i18n.createTranslator({ en, ru }, 'en')('error.value', { error: 'offline' }), 'Error: offline');
+```
+
+- [ ] **Step 2: Run the test and confirm RED**
+
+Run: `node scripts/test-i18n.js`
+
+Expected: FAIL because `shared/i18n.js` and catalogs do not exist.
+
+- [ ] **Step 3: Implement the minimal shared runtime**
+
+Implement an IIFE exporting the four functions. `loadCatalogs(loadJSON)` must call `loadJSON('en')` and `loadJSON('ru')`; translation lookup order is selected catalog, English catalog, explicit fallback, key. Interpolation replaces `{name}` only when `params` owns that property.
+
+Catalogs must define identical keys for:
+
+```text
+popup.subtitle
+label.receiver
+label.pending
+label.url
+label.file
+label.receiverUrl
+label.pairingToken
+label.language
+action.sendPage
+action.sendFile
+action.retryPending
+action.save
+hint.contextMenu
+receiver.online
+receiver.offline
+receiver.unknown
+language.system
+language.en
+language.ru
+status.sending
+status.queued
+status.done
+status.readingFile
+status.saved
+error.chooseFile
+error.fileTooLarge
+error.invalidReceiverUrl
+error.value
+context.sendPage
+context.sendSelection
+context.sendLink
+```
+
+- [ ] **Step 4: Add the test to `npm test` and verify GREEN**
+
+Set:
+
+```json
+"test": "node scripts/test-protocol.js && node scripts/test-i18n.js && node scripts/test-popup-settings.js"
+```
+
+Run: `node scripts/test-i18n.js`
+
+Expected: `browser extension localization runtime tests passed`.
+
+- [ ] **Step 5: Commit the shared contract**
+
+```bash
+git add shared/i18n.js shared/locales scripts/test-i18n.js package.json
+git commit -m "feat: add browser extension localization runtime"
+```
+
+---
+
+### Task 2: Persisted Language and Localized Context Menus
+
+**Files:**
+
+- Modify: `shared/background.js`
+- Modify: `chromium/manifest.json`
+- Modify: `firefox/manifest.json`
+- Create: `scripts/test-background-i18n.js`
+
+**Interfaces:**
+
+- Consumes: `VerstakBrowserI18n.loadCatalogs`, `normalizePreference`, `resolveLocale`, `createTranslator`.
+- Produces: persisted `settings.language` and context-menu recreation after `saveSettings`.
+
+- [ ] **Step 1: Write the failing background test**
+
+Load `protocol.js`, `queue.js`, `i18n.js`, and `background.js` into `vm` with fake storage/context-menu APIs. Seed `settings.language = 'ru'`, trigger `runtime.onInstalled`, and assert:
+
+```js
+assert.deepStrictEqual(menuTitles, [
+ 'Отправить страницу в Верстак',
+ 'Отправить выделение в Верстак',
+ 'Отправить ссылку в Верстак',
+]);
+```
+
+Send a `saveSettings` message with `{ receiverUrl, receiverToken, language: 'en' }`, then assert stored receiver fields are unchanged and menu titles become English.
+
+- [ ] **Step 2: Run the test and confirm RED**
+
+Run: `node scripts/test-background-i18n.js`
+
+Expected: FAIL because background defaults contain no language and menu titles are literal English.
+
+- [ ] **Step 3: Implement background localization**
+
+Add `language: 'system'` to `DEFAULT_SETTINGS`. Normalize it in `getSettings`/`saveSettings`. Load catalogs with:
+
+```js
+function loadLocaleCatalogs() {
+ return localeCatalogs || i18n.loadCatalogs(function (locale) {
+ return fetch(ext.runtime.getURL('locales/' + locale + '.json')).then(function (response) {
+ if (!response.ok) throw new Error('catalog load failed: ' + locale);
+ return response.json();
+ });
+ });
+}
+```
+
+Make `setupContextMenus()` resolve settings plus catalogs, choose
+`ext.i18n.getUILanguage()` with English fallback, and create the three menu
+titles via `t('context.sendPage')`, `t('context.sendSelection')`, and
+`t('context.sendLink')`. Call it after language settings are saved.
+
+- [ ] **Step 4: Load `i18n.js` before background code in both manifests**
+
+- Chromium service worker remains bundled by the build concatenation order.
+- Firefox `background.scripts` becomes `protocol.js`, `api.js`, `queue.js`, `i18n.js`, `background.js`.
+
+Also append `node scripts/test-background-i18n.js` to the `test` script in
+`package.json` now that the test file exists.
+
+- [ ] **Step 5: Verify and commit**
+
+Run: `node scripts/test-background-i18n.js`
+
+Expected: `browser extension background localization tests passed`.
+
+```bash
+git add shared/background.js chromium/manifest.json firefox/manifest.json scripts/test-background-i18n.js
+git commit -m "feat: localize browser extension context menus"
+```
+
+---
+
+### Task 3: Popup Language Selector and Live Translation
+
+**Files:**
+
+- Modify: `shared/popup/popup.html`
+- Modify: `shared/popup/popup.js`
+- Modify: `shared/popup/popup.css`
+- Modify: `scripts/test-popup-settings.js`
+
+**Interfaces:**
+
+- Consumes: state `settings.language` from background and the shared translator.
+- Produces: immediate popup translation plus a `saveSettings` message containing receiver URL, token, and language.
+
+- [ ] **Step 1: Extend the popup test and confirm RED**
+
+Add fake elements for every localized ID plus `language-select`, mock catalog fetches, `browser.i18n.getUILanguage()`, and `document.documentElement.lang`. Assert initial `system` with `ru-RU` renders Russian. Change select value to `en`, dispatch `change`, flush promises, then assert:
+
+```js
+assert.strictEqual(elements['capture-page'].textContent, 'Send Page');
+assert.strictEqual(elements['receiver-state'].textContent, 'Unknown');
+assert.strictEqual(document.documentElement.lang, 'en');
+assert.strictEqual(savedSettings.language, 'en');
+assert.strictEqual(savedSettings.receiverUrl, initialState.settings.receiverUrl);
+assert.strictEqual(savedSettings.receiverToken, initialState.settings.receiverToken);
+```
+
+- [ ] **Step 2: Add popup markup**
+
+Load `../i18n.js` before `popup.js`, give all static user-visible elements stable IDs, and add:
+
+```html
+
+
+```
+
+- [ ] **Step 3: Implement asynchronous popup initialization and live switch**
+
+Load both catalogs through `ext.runtime.getURL`, resolve the locale from saved
+preference plus browser UI language, and apply all static text through one
+`applyLocale(preference)` function. `render(state)` localizes
+online/offline/unknown. Known statuses and validations use catalog keys; raw
+error messages are wrapped only when needed by `error.value`.
+
+The select `change` handler must call `applyLocale` before awaiting background
+storage, then send all three settings fields. The existing Save button also
+sends the selected language.
+
+- [ ] **Step 4: Style the select consistently and verify GREEN**
+
+Share the existing input box model/colors with `select` and keep the popup
+minimum width unchanged.
+
+Run: `node scripts/test-popup-settings.js`
+
+Expected: `browser extension popup localization/settings tests passed`.
+
+- [ ] **Step 5: Commit**
+
+```bash
+git add shared/popup scripts/test-popup-settings.js
+git commit -m "feat: add browser extension language selector"
+```
+
+---
+
+### Task 4: Distribution Packaging, Documentation, and Full Verification
+
+**Files:**
+
+- Modify: `scripts/build-extension.js`
+- Modify: `README.md`
+- Test: `scripts/test-i18n.js`
+- Test: `scripts/test-background-i18n.js`
+- Test: `scripts/test-popup-settings.js`
+
+**Interfaces:**
+
+- Consumes: shared runtime/catalogs and updated manifests.
+- Produces: complete `dist/chromium` and `dist/firefox` extension directories.
+
+- [ ] **Step 1: Add failing build-content assertions**
+
+Extend `scripts/test-i18n.js` to run after build when `dist` exists and assert
+both targets contain:
+
+```text
+i18n.js
+locales/en.json
+locales/ru.json
+```
+
+- [ ] **Step 2: Update the build**
+
+For Chromium, concatenate `shared/i18n.js` before `shared/background.js` and
+also copy it as `dist/chromium/i18n.js` for popup use. For Firefox, copy
+`shared/i18n.js` beside background scripts. Copy both JSON catalogs to each
+target's `locales/` directory.
+
+- [ ] **Step 3: Document the selector**
+
+Add a README section stating that popup settings provide persisted
+`System / English / Russian`, that System uses browser UI language, and that
+extension/desktop preferences are independent.
+
+- [ ] **Step 4: Run complete verification**
+
+```bash
+npm test
+npm run build
+npm test
+git diff --check
+```
+
+Expected:
+
+- protocol, runtime, popup, and background tests pass;
+- both browser distributions build;
+- post-build content assertions pass;
+- no whitespace errors.
+
+- [ ] **Step 5: Commit packaging and docs**
+
+```bash
+git add scripts/build-extension.js README.md scripts/test-i18n.js
+git commit -m "build: package browser extension locale catalogs"
+```