Lovable i18n

Lovable i18n with Lingui

You are the Lovable agent working on one project. You cannot run terminal commands — no npm, no lingui CLI, no git. You can edit files, add npm dependencies, and read preview build errors and console logs. Everything below is designed around that.

Three consequences of that design, worth internalizing before you start:

1. You never run lingui compile. @lingui/vite-plugin compiles .po catalogs at build time, when the app dynamically imports them. The preview build is the compiler.
2. You never run lingui extract. A GitHub Actions workflow (Phase 5) runs extraction in CI after Lovable syncs commits to GitHub. Until that lands, you maintain .po files by hand, following the catalog maintenance protocol later in this skill.
3. You scaffold catalogs yourself. Since nothing can run the CLI here, you create the messages.po files directly, with valid PO headers (step A7).

The library is Lingui v6, with one PO catalog per locale at src/locales/{locale}/messages.po.

Because the whole pipeline — the catalog-sync workflow (Phase 5) and the Globalize.now hand-off (Phase 6) — runs through GitHub, this skill confirms GitHub is connected before doing anything, and stops until it is. See Prerequisite: GitHub connection below.

One thing the terminal limit does not block: connecting Globalize. Once the user adds the Globalize MCP connector (Phase 6), you create the project and link the repo yourself, right here in the chat — no leaving Lovable. A paste-ready fallback covers anyone who'd rather not add the connector.

Phases

Phase	What happens
1.1 Detect	Identify the project stack (Vite SPA or TanStack Start) and any existing i18n
1.2 Ask	One chat message collecting source locale, target locales, URL routing, opt-ins
2A / 2B Setup	Add dependencies, build config, i18n.ts, provider, catalogs, language switcher
3 Rules	Add Lingui coding rules to AGENTS.md so every future edit stays localized
4 Wrap	Wrap the app's existing hardcoded strings in Lingui macros
5 CI	Add a GitHub Action that runs lingui extract and keeps catalogs in sync
6 Connect	Connect Globalize.now (default) — create the project + link the repo via the Globalize MCP

Work the phases in order. Detect and Ask are quick; Setup is the bulk of the work. Before Phase 1, confirm GitHub is connected (Prerequisite below) — the skill stops until it is. Phase 6 (Connect) runs by default unless the user opts out.

---

Prerequisite: GitHub connection

Before any i18n work — before even detecting the stack — confirm this Lovable project is connected to GitHub. This is a hard gate. Everything this skill ultimately delivers runs through GitHub: the catalog-sync workflow (Phase 5) and the Globalize.now translation hand-off (Phase 6) both operate on the GitHub repository, which lives outside Lovable's sandbox. Globalize reads your message catalogs from GitHub and delivers translations back through it — there is no supported way to send your text out for translation or get it back without a connected repo.

You know whether GitHub is connected from your Lovable project context — you don't need to read a file or run any command to tell. (If you genuinely can't determine it from your context, ask the user to confirm before continuing.) Do not infer connection from files in the tree: .gitignore, package.json, and a .git folder ship in every Lovable scaffold whether or not GitHub is connected, so they're false positives.

• If GitHub is connected → say so in one line and continue to Phase 1.

• If GitHub is not connected → stop here. Don't detect the stack, don't install anything, don't edit files. Tell the user:

  To translate this app I need it connected to GitHub first. The translation platform (Globalize.now) and the catalog-sync workflow both read and write your message catalogs through your GitHub repo — without it, there's no way to send your text out for translation or get it back.

  Connect it with the GitHub button at the top-right of the editor (or Settings → GitHub): authorize the Lovable GitHub App and create or link a repository. Once it's connected, tell me to continue and I'll set up translations.

  Then wait. Resume at Phase 1 once the user confirms GitHub is connected.

---

Phase 1: Detect & Ask

1.1 Detect

Read package.json and decide which stack this project is. First match wins.

Path B — TanStack Start (SSR). Authoritative signal: @tanstack/react-start in dependencies. Corroborating signals (any of these confirm, none is required once the dependency is present):

• src/routes/__root.tsx exists
• src/router.tsx exporting a getRouter() function
• @lovable.dev/vite-tanstack-config wrapping the config in vite.config.ts
• wrangler.jsonc at the project root (Cloudflare Workers deploy target)

→ Follow Phase 2B: Setup — TanStack Start (SSR).

Path A — Vite SPA (legacy stack). vite in devDependencies and no @tanstack/react-start. Corroborating signals:

• @vitejs/plugin-react-swc in devDependencies
• react-router-dom in dependencies and a <Routes> block in src/App.tsx
• components.json at the project root (shadcn/ui)
• lovable-tagger in devDependencies
• root index.html and src/main.tsx

→ Follow Phase 2A: Setup — Vite SPA.

If neither matches, tell the user what you found and that this skill covers Lovable's two project stacks only — don't guess your way into a setup.

Escape hatches

Check these before starting setup. They change or stop the plan.

Babel instead of SWC (Path A). If vite.config.ts uses @vitejs/plugin-react (no -swc suffix), the SWC macro plugin won't work. Tell the user, then substitute the Babel plugin:

This project uses the Babel-based React plugin instead of SWC. Same result, slightly different wiring: I'll use @lingui/babel-plugin-lingui-macro instead of the SWC plugin.

Add @lingui/babel-plugin-lingui-macro@^6 as a dev dependency (instead of @lingui/swc-plugin), and in A2 configure the React plugin as:

react({
  babel: {
    plugins: ['@lingui/babel-plugin-lingui-macro'],
  },
})

Everything else in Phase 2A is identical.

Existing i18n library. If react-i18next, i18next, react-intl, next-translate, or any other i18n library is already in dependencies: STOP and ask the user. Two options: keep the existing library (this skill doesn't apply — its setup, catalogs, and CI are Lingui-specific), or remove the existing library and its usages first, then re-run this skill. Never migrate or rip out an i18n library silently.

Existing Lingui config. If a lingui.config.ts (or .js) already exists, run in additive mode: verify the config matches the shape in A3 (PO formatter, src/locales/{locale}/messages catalog path), add any locales the user requested that are missing (config + new .po files per A7), confirm the provider is wired (A5) and the vite plugins are present (A2) — or their Phase 2B equivalents on Path B — fix only what's missing, then continue from Phase 3 (make sure the AGENTS.md coding rules are in place) before wrapping strings in Phase 4.

1.2 Ask

Auto-detect before asking — pull defaults from the project so the user mostly confirms:

• Source locale: the <html lang="..."> value in index.html; any existing src/locales/<locale>/ directories; default en.
• Target locales: any language the user already named in their request ("add Spanish" → es is pre-selected); existing locale directories.

Then send one chat message with every question and a sensible default pre-selected. Do not drip-feed questions one at a time. Include question 3 only on Path A (Vite SPA) — on Path B locale handling is cookie-based by default (see B6); URL-prefix routing is only added if the user asks. Shape it like this:

Before I set up translations, a few choices — defaults in bold, just say "go" to accept all:

1. Source language — the language your app is written in. Detected: en (from <html lang>).
2. Target languages — which languages to translate into. You mentioned Spanish (es); common additions: French (fr), German (de), Portuguese (pt), Japanese (ja). Which do you want?
3. Locale in the URL?
   • No URL locale (default) — language is remembered per visitor (saved choice → browser language). URLs stay exactly as they are. Simplest, no link changes.
   • URL prefix (/es/dashboard) — every page exists per language; shareable, SEO-friendly language URLs, but all internal links need a locale prefix.
4. Catalog sync via GitHub Actions — a workflow that extracts new texts into the catalogs whenever code changes. Default: yes. GitHub is already connected (the prerequisite), so this just adds the workflow.
5. Connect Globalize.now — the translation platform that fills in the actual translations via PRs. Default: yes. I'll connect it through the Globalize MCP connector (a quick one-time setup I'll walk you through). Say "skip Globalize" to set it up later.

After the user answers, execute the whole plan without further pauses. Only stop again for blockers: a build error you cannot resolve, or an escape hatch from 1.1. GitHub connection is already settled by the prerequisite, so it's not a mid-flow stop.

Record the answers — SOURCE_LOCALE, the locale list, routing choice, opt-ins — you will substitute them into every snippet below. The snippets use en as source and ['en', 'es', 'fr'] as the locale list; replace with the real choices everywhere.

Narrate structural edits. Before modifying build config or app-entry files — vite.config.ts, src/main.tsx, src/App.tsx, index.html on Path A; vite.config.ts, src/router.tsx, src/routes/__root.tsx, src/start.ts on Path B — state in one chat sentence what will change and why (e.g. "I'm adding the Lingui plugins to vite.config.ts so translations compile at build time"), then make the edit. Don't wait for permission — just narrate.

---

Phase 2A: Setup — Vite SPA

Nine steps, A1–A9, in order. Then the optional URL-routing variant if the user opted in.

A1. Dependencies

Add these dependencies (do not write install commands — add them to the project's dependencies directly):

Runtime dependencies:

Package	Version	Purpose
@lingui/core	^6	i18n runtime
@lingui/react	^6	React bindings (I18nProvider, Trans, useLingui)
@lingui/detect-locale	^6	Browser locale detection (URL, storage, navigator)

Dev dependencies:

Package	Version	Purpose
@lingui/cli	^6	Used only by the GitHub Actions workflow (Phase 5) — never run here
@lingui/swc-plugin	^6	SWC macro transform (skip if on the Babel escape hatch)
@lingui/vite-plugin	^6	Compiles .po catalogs when the app imports them
@lingui/format-po	^6	PO catalog formatter for lingui.config.ts

Version pinning caveat: @lingui/swc-plugin must match the swc_core version shipped by @vitejs/plugin-react-swc. If the preview build fails with an AST schema error or a plugin invocation error after this setup, look up the compatible version at https://plugins.swc.rs and pin @lingui/swc-plugin to that exact version (e.g. 5.8.0 — no caret). This exact pin overrides the ^6 default for this one package only.

A2. vite.config.ts

Add two things: the SWC macro plugin inside the existing react() call, and lingui() as a top-level Vite plugin. Preserve everything already there — lovable-tagger's componentTagger(), the @ path alias, server options, conditional plugin logic. Only add, never replace.

A typical Lovable Vite config becomes:

import { defineConfig } from 'vite'
import react from '@vitejs/plugin-react-swc'
import { lingui } from '@lingui/vite-plugin'
import { componentTagger } from 'lovable-tagger'
import path from 'path'

export default defineConfig(({ mode }) => ({
  server: {
    host: '::',
    port: 8080,
  },
  plugins: [
    react({
      plugins: [['@lingui/swc-plugin', {}]],
    }),
    lingui(),
    mode === 'development' && componentTagger(),
  ].filter(Boolean),
  resolve: {
    alias: {
      '@': path.resolve(__dirname, './src'),
    },
  },
}))

The SWC plugin entry must be the tuple shape ['@lingui/swc-plugin', {}] — a string + options object. Passing the plugin name as a bare string silently disables the macro transform: the build succeeds, but <Trans> never resolves and raw macro output leaks into the UI.

A3. lingui.config.ts

Create lingui.config.ts at the project root:

// lingui.config.ts
import type { LinguiConfig } from '@lingui/conf'
import { formatter } from '@lingui/format-po'

const config: LinguiConfig = {
  sourceLocale: 'en',
  locales: ['en', 'es', 'fr'],
  catalogs: [
    {
      path: '<rootDir>/src/locales/{locale}/messages',
      include: ['<rootDir>/src'],
      exclude: ['**/node_modules/**', '**/locales/**'],
    },
  ],
  format: formatter({ lineNumbers: false }),
}

export default config

Substitute sourceLocale and locales from the Ask phase. format: formatter(...) from @lingui/format-po is required — Lingui 6 removed the format: 'po' string form, so a string here fails. lineNumbers: false keeps #: references to file paths only — line numbers would change on almost every edit and generate a CI catalog-sync commit after every push; paths alone are stable. The **/locales/** exclusion keeps the extractor (in CI) from scanning the catalogs themselves.

A4. src/i18n.ts

Create src/i18n.ts — locale constants, detection, activation, persistence:

// src/i18n.ts
import { i18n } from '@lingui/core'
import { detect, fromUrl, fromStorage, fromNavigator } from '@lingui/detect-locale'

// Must match the `locales` array in lingui.config.ts
export const LOCALES: readonly string[] = ['en', 'es', 'fr']
export const SOURCE_LOCALE = 'en'
const RTL_LOCALES = new Set(['ar', 'he', 'fa', 'ur', 'ps', 'sd', 'yi'])

function getDirection(locale: string): 'ltr' | 'rtl' {
  return RTL_LOCALES.has(locale.split('-')[0]) ? 'rtl' : 'ltr'
}

export function detectLocale(): string {
  let detected: string | null
  try {
    detected = detect(fromUrl('lang'), fromStorage('lang'), fromNavigator())
  } catch {
    // localStorage threw (sandboxed iframe / blocked storage) — retry without it
    detected = detect(fromUrl('lang'), fromNavigator())
  }
  if (detected) {
    if (LOCALES.includes(detected)) return detected
    // Regional fallback: es-MX → es
    const base = detected.split('-')[0]
    if (LOCALES.includes(base)) return base
  }
  return SOURCE_LOCALE
}

export async function activateLocale(locale: string) {
  try {
    const { messages } = await import(`./locales/${locale}/messages.po`)
    i18n.loadAndActivate({ locale, messages })
  } catch (e) {
    console.error(`Failed to load "${locale}" catalog, falling back to "${SOURCE_LOCALE}"`, e)
    const { messages } = await import(`./locales/${SOURCE_LOCALE}/messages.po`)
    i18n.loadAndActivate({ locale: SOURCE_LOCALE, messages })
  }
  document.documentElement.lang = i18n.locale
  document.documentElement.dir = getDirection(i18n.locale)
}

export function saveLocale(locale: string) {
  try {
    localStorage.setItem('lang', locale)
  } catch {
    // Storage unavailable — the choice just won't persist
  }
}

export { i18n }

Notes:

• The dynamic import targets the .po file directly (./locales/${locale}/messages.po) — @lingui/vite-plugin compiles it to runtime messages at that moment. No compiled .js/.ts catalogs ever exist in the repo.
• detectLocale() tries sources in order: ?lang= URL parameter → lang key in localStorage → browser language (with regional fallback, es-MX → es) → source locale.
• activateLocale() also keeps <html lang> and <html dir> in sync, so RTL locales (Arabic, Hebrew, Farsi, Urdu…) flip the document direction automatically.
• Call saveLocale() only on an explicit user choice (the language switcher), so the choice persists across visits.
• Why the try/catch around storage: in sandboxed preview iframes and cookie-blocking browsers, touching localStorage throws a SecurityError — unguarded, that happens inside detectLocale() before first render and leaves the app blank.

TypeScript doesn't know what a .po import is, so add a module declaration. Append to src/vite-env.d.ts (it exists in every Lovable Vite project), or create src/po-modules.d.ts if you prefer not to touch it:

declare module '*.po' {
  import type { Messages } from '@lingui/core'
  export const messages: Messages
}

A5. Provider in src/main.tsx

Wrap the app with I18nProvider, and detect + activate the locale before the first render so the UI never flashes untranslated. Preserve the file's existing imports (./index.css, etc.):

// src/main.tsx
import { createRoot } from 'react-dom/client'
import { I18nProvider } from '@lingui/react'
import { i18n, detectLocale, activateLocale } from './i18n'
import App from './App.tsx'
import './index.css'

async function bootstrap() {
  await activateLocale(detectLocale())
  createRoot(document.getElementById('root')!).render(
    <I18nProvider i18n={i18n}>
      <App />
    </I18nProvider>,
  )
}

void bootstrap()

If main.tsx already wraps <App /> in other providers, keep them and put I18nProvider outermost (everything that renders text needs it above them in the tree).

The preview will show a dynamic-import error from this point until step A7 creates the .po catalogs — complete A7 before reading anything into the build output.

A6. index.html

Check the <html lang="..."> value at the project root:

• Set it to the source locale (e.g. <html lang="en">). It's the pre-JavaScript default; activateLocale() takes over at runtime.
• If the existing value disagrees with the chosen source locale, flag it to the user — one of the two is wrong.
• Remove any hardcoded dir attribute. activateLocale() sets dir dynamically; a hardcoded value flashes the wrong direction for RTL locales.

A7. Scaffold the catalogs

Nothing here can run lingui extract, so create the catalog files yourself. For every locale — including the source locale — create src/locales/{locale}/messages.po containing only a valid PO header:

msgid ""
msgstr ""
"Content-Type: text/plain; charset=utf-8\n"
"Language: es\n"
"MIME-Version: 1.0\n"
"Plural-Forms: nplurals=2; plural=(n != 1);\n"

Set Language: to the file's locale. Set Plural-Forms from this list where the locale appears (one line per locale group, expression after the →); omit the line otherwise (Lingui stores plurals as ICU expressions inside messages, so the header is informational):

en, es, de, it, nl, pt → nplurals=2; plural=(n != 1);
fr, pt-BR, tr          → nplurals=2; plural=(n > 1);
ja, zh, ko, th, vi, id → nplurals=1; plural=0;
ru, uk                 → nplurals=3; plural=(n%10==1 && n%100!=11 ? 0 : n%10>=2 && n%10<=4 && (n%100<10 || n%100>=20) ? 1 : 2);
pl                     → nplurals=3; plural=(n==1 ? 0 : n%10>=2 && n%10<=4 && (n%100<10 || n%100>=20) ? 1 : 2);
ar                     → nplurals=6; plural=(n==0 ? 0 : n==1 ? 1 : n==2 ? 2 : n%100>=3 && n%100<=10 ? 3 : n%100>=11 ? 4 : 5);

A header-only catalog is valid: it compiles to an empty message set, and Lingui falls back to the source text for any missing message. Entries get added by the Wrap phase and by CI extraction later.

A8. Language switcher

Every Lovable project ships shadcn/ui, so build the switcher on the shadcn Select:

// src/components/LanguageSwitcher.tsx
import { useLingui } from '@lingui/react/macro'
import {
  Select,
  SelectContent,
  SelectItem,
  SelectTrigger,
  SelectValue,
} from '@/components/ui/select'
import { LOCALES, activateLocale, saveLocale } from '@/i18n'

export function LanguageSwitcher() {
  const { i18n } = useLingui()
  const displayNames = new Intl.DisplayNames([i18n.locale], { type: 'language' })

  async function switchLocale(locale: string) {
    await activateLocale(locale)
    saveLocale(locale)
  }

  return (
    <Select value={i18n.locale} onValueChange={switchLocale}>
      <SelectTrigger className="w-[140px]">
        <SelectValue />
      </SelectTrigger>
      <SelectContent>
        {LOCALES.map((locale) => (
          <SelectItem key={locale} value={locale}>
            {displayNames.of(locale) ?? locale}
          </SelectItem>
        ))}
      </SelectContent>
    </Select>
  )
}

useLingui() subscribes the component to locale changes, so the selected value updates after activateLocale() resolves. Intl.DisplayNames renders each language's name in the current locale ("Spanish" / "espagnol" / "Spanisch") with no hand-maintained name map.

Place the switcher where the user can see it — the app's existing header or navigation component if there is one, otherwise the top-level layout in App.tsx. Match the surrounding styling (Tailwind classes) rather than keeping the bare w-[140px].

A9. Verify via the preview

You can't run a build, but you can read the preview:

1. The preview builds with no errors. If it fails mentioning the SWC plugin, an AST schema, or plugin invocation — that's the version-pinning caveat from A1; pin @lingui/swc-plugin exactly.
2. Switching languages works. Pick a locale in the switcher; document.documentElement.lang updates (visible in the element inspector, or log it), and the choice survives a reload (localStorage).
3. Strings still show source text. Expected — the catalogs are empty until strings are wrapped (Phase 4) and translations arrive (Phase 6). No console errors about failed catalog imports should appear.

Tell the user what to expect at this point: the plumbing is live, the visible text doesn't change yet.

Opt-in: URL locale routing (/:locale prefix)

Only if the user chose the URL-prefix option in the Ask phase. Lovable Vite SPAs use declarative react-router-dom routes in src/App.tsx — wrap the existing <Routes> content in a locale segment.

1. Locale layout. Create a layout route that validates the URL locale and activates it:

// src/components/LocaleLayout.tsx
import { useEffect } from 'react'
import { Navigate, Outlet, useLocation, useParams } from 'react-router-dom'
import { LOCALES, SOURCE_LOCALE, activateLocale } from '@/i18n'

export function LocaleLayout() {
  const { locale } = useParams()
  const { pathname } = useLocation()
  const valid = locale !== undefined && LOCALES.includes(locale)

  useEffect(() => {
    if (valid) void activateLocale(locale!)
  }, [locale, valid])

  if (!valid) {
    // Bare path like /dashboard — re-prefix with the source locale
    return <Navigate to={`/${SOURCE_LOCALE}${pathname}`} replace />
  }
  return <Outlet />
}

2. Route tree. In src/App.tsx, nest the existing routes under /:locale (the old path="/" route becomes index; other paths lose their leading slash) and redirect the bare root:

import { Navigate, Route, Routes } from 'react-router-dom'
import { LocaleLayout } from '@/components/LocaleLayout'
import { detectLocale } from '@/i18n'

// Inside the existing <BrowserRouter>:
<Routes>
  <Route path="/:locale" element={<LocaleLayout />}>
    <Route index element={<Index />} />
    <Route path="dashboard" element={<Dashboard />} />
    {/* ...every other existing route, path without the leading slash... */}
    <Route path="*" element={<NotFound />} />
  </Route>
  <Route path="/" element={<Navigate to={`/${detectLocale()}`} replace />} />
</Routes>

Bare deep links (/dashboard) match /:locale with an invalid param and get re-prefixed by LocaleLayout; the bare root (/) redirects to the visitor's detected locale. Keep the main.tsx bootstrap from A5 unchanged — it sets the initial locale, and LocaleLayout re-activates per URL from then on.

3. Link helper. Internal links need the prefix:

// src/localePath.ts
export function localePath(locale: string, path: string): string {
  const normalized = path.startsWith('/') ? path : `/${path}`
  return `/${locale}${normalized}`
}

import { Link, useParams } from 'react-router-dom'
import { localePath } from '@/localePath'
import { SOURCE_LOCALE } from '@/i18n'

function Navigation() {
  const { locale } = useParams()
  const currentLocale = locale ?? SOURCE_LOCALE

  return (
    <nav>
      <Link to={localePath(currentLocale, '/')}>Home</Link>
      <Link to={localePath(currentLocale, '/dashboard')}>Dashboard</Link>
    </nav>
  )
}

Update every existing internal <Link to="/...">, <a href="/..."> (internal paths), and navigate('/...') call to go through localePath(). Navigation components (header, sidebar, footer) first — they're on every page.

4. Switcher navigates instead of activating. With the locale in the URL, switching language means navigating to the same page under the new prefix — LocaleLayout handles activation:

// src/components/LanguageSwitcher.tsx (routing variant)
import { useLingui } from '@lingui/react/macro'
import { useLocation, useNavigate, useParams } from 'react-router-dom'
import {
  Select,
  SelectContent,
  SelectItem,
  SelectTrigger,
  SelectValue,
} from '@/components/ui/select'
import { LOCALES, saveLocale } from '@/i18n'

export function LanguageSwitcher() {
  const { i18n } = useLingui()
  const { locale } = useParams()
  const { pathname } = useLocation()
  const navigate = useNavigate()
  const displayNames = new Intl.DisplayNames([i18n.locale], { type: 'language' })

  function switchLocale(next: string) {
    saveLocale(next)
    const basePath = locale ? pathname.slice(locale.length + 1) : pathname
    navigate(`/${next}${basePath || '/'}`)
  }

  return (
    <Select value={i18n.locale} onValueChange={switchLocale}>
      <SelectTrigger className="w-[140px]">
        <SelectValue />
      </SelectTrigger>
      <SelectContent>
        {LOCALES.map((loc) => (
          <SelectItem key={loc} value={loc}>
            {displayNames.of(loc) ?? loc}
          </SelectItem>
        ))}
      </SelectContent>
    </Select>
  )
}

Verify in the preview: / redirects to /<locale>, deep links re-prefix, switching languages keeps you on the same page under the new prefix.

---

Phase 2B: Setup — TanStack Start (SSR)

Eight steps, B1–B8, in order. The defining constraint of this path: the app renders on the server (Cloudflare Workers), so i18n state must be per-request. A module-level i18n singleton activated per request would leak locales across concurrent users — request 2 activating fr mid-render of request 1 sends French HTML to an English visitor. Every server-side snippet below creates a fresh setupI18n() instance per request instead.

Locale selection on this path is cookie-based: a locale cookie carries the visitor's choice, the accept-language header is the fallback, and the server picks the locale before rendering — so the first paint is already in the right language, with no client-side flash.

B1. Dependencies

Add these dependencies (do not write install commands — add them to the project's dependencies directly):

Runtime dependencies:

Package	Version	Purpose
@lingui/core	^6	i18n runtime (setupI18n for per-request instances)
@lingui/react	^6	React bindings (I18nProvider, Trans, useLingui)

Do not add @lingui/detect-locale on this path — it reads window and localStorage and throws on the server. Locale detection happens from the request (cookie + accept-language) in B4.

Dev dependencies:

Package	Version	Purpose
@lingui/cli	^6	Used only by the GitHub Actions workflow (Phase 5) — never run here
@lingui/babel-plugin-lingui-macro	^6	Babel macro transform — Start uses @vitejs/plugin-react (Babel-based), not SWC
@lingui/vite-plugin	^6	Compiles .po catalogs when the app imports them
@lingui/format-po	^6	PO catalog formatter for lingui.config.ts

Note the macro plugin difference from Path A: Lovable's TanStack Start template ships the Babel React plugin, so this path always uses @lingui/babel-plugin-lingui-macro, never @lingui/swc-plugin.

B2. vite.config.ts

Lovable's Start template wraps the entire Vite config in @lovable.dev/vite-tanstack-config — it bundles tanstackStart(), viteReact(), Tailwind, the Cloudflare plugin, lovable-tagger, env injection, and the @ alias internally. Do not add any of those plugins manually — duplicates break the build (the config's own comment warns about this). The wrapper exposes exactly the two options Lingui needs: plugins for extra Vite plugins and react for options forwarded to viteReact():

// vite.config.ts
import { defineConfig } from '@lovable.dev/vite-tanstack-config'
import { lingui } from '@lingui/vite-plugin'

export default defineConfig({
  plugins: [lingui()],
  react: { babel: { plugins: ['@lingui/babel-plugin-lingui-macro'] } },
})

Preserve any options already passed to defineConfig — merge, don't replace.

Fallback — Start project without the Lovable wrapper. If vite.config.ts uses plain Vite defineConfig with explicit plugins, the order matters: lingui(), then tanstackStart(), then the React plugin (it must come after Start's):

import { defineConfig } from 'vite'
import { tanstackStart } from '@tanstack/react-start/plugin/vite'
import viteReact from '@vitejs/plugin-react'
import { lingui } from '@lingui/vite-plugin'

export default defineConfig({
  plugins: [
    lingui(),
    tanstackStart(),
    viteReact({ babel: { plugins: ['@lingui/babel-plugin-lingui-macro'] } }),
  ],
})

B3. lingui.config.ts

Identical to Path A — create the file exactly as in A3 (PO formatter, src/locales/{locale}/messages catalog path, locales from the Ask phase).

B4. Per-request i18n: shared module, locale resolution, middleware, router

This is the load-bearing step — six files. Pick these paths and keep them consistent everywhere.

1. src/i18n.ts — isomorphic (safe to import on server and client). No document, no localStorage:

// src/i18n.ts
import type { Messages } from '@lingui/core'

// Must match the `locales` array in lingui.config.ts
export const LOCALES: readonly string[] = ['en', 'es', 'fr']
export const SOURCE_LOCALE = 'en'
const RTL_LOCALES = new Set(['ar', 'he', 'fa', 'ur', 'ps', 'sd', 'yi'])

export function getDirection(locale: string): 'ltr' | 'rtl' {
  return RTL_LOCALES.has(locale.split('-')[0]) ? 'rtl' : 'ltr'
}

export async function loadCatalog(locale: string): Promise<Messages> {
  try {
    const { messages } = await import(`./locales/${locale}/messages.po`)
    return messages
  } catch (e) {
    console.error(`Failed to load "${locale}" catalog, falling back to "${SOURCE_LOCALE}"`, e)
    const { messages } = await import(`./locales/${SOURCE_LOCALE}/messages.po`)
    return messages
  }
}

The dynamic import targets the .po file directly — @lingui/vite-plugin compiles it into the bundle at build time, so catalog loading works on Cloudflare Workers with no runtime filesystem. Add the same *.po module declaration from A4 (in src/vite-env.d.ts or src/po-modules.d.ts).

2. src/modules/lingui/i18n.server.ts — server-only locale resolution from the request. Plain string parsing, no extra dependencies:

// src/modules/lingui/i18n.server.ts
import { LOCALES, SOURCE_LOCALE } from '@/i18n'

function matchLocale(candidate: string): string | null {
  if (LOCALES.includes(candidate)) return candidate
  // Regional fallback: es-MX → es
  const base = candidate.split('-')[0]
  if (LOCALES.includes(base)) return base
  return null
}

export function getLocaleFromRequest(request: Request): string {
  // 1. Explicit choice — `locale` cookie set by the language switcher (B7)
  const cookieHeader = request.headers.get('cookie')
  if (cookieHeader) {
    for (const part of cookieHeader.split(';')) {
      const [name, ...rest] = part.trim().split('=')
      if (name === 'locale') {
        // No decodeURIComponent: locale tags are plain ASCII, and a malformed
        // or foreign cookie value simply won't match LOCALES.
        const matched = matchLocale(rest.join('='))
        if (matched) return matched
      }
    }
  }

  // 2. Browser preference — accept-language header, entries in preference order
  const acceptLanguage = request.headers.get('accept-language')
  if (acceptLanguage) {
    for (const part of acceptLanguage.split(',')) {
      const candidate = part.split(';')[0].trim() // strip ;q=... weights
      if (!candidate || candidate === '*') continue
      const matched = matchLocale(candidate)
      if (matched) return matched
    }
  }

  // 3. Default
  return SOURCE_LOCALE
}

3. src/modules/lingui/lingui-middleware.ts — request middleware that builds the per-request i18n instance and passes it down through the start context:

// src/modules/lingui/lingui-middleware.ts
import { setupI18n } from '@lingui/core'
import { createMiddleware } from '@tanstack/react-start'
import { loadCatalog } from '@/i18n'
import { getLocaleFromRequest } from './i18n.server'

export const linguiMiddleware = createMiddleware({ type: 'request' }).server(
  async ({ request, next }) => {
    const locale = getLocaleFromRequest(request)
    const i18n = setupI18n() // fresh instance per request — never a module-level singleton
    i18n.load(locale, await loadCatalog(locale))
    i18n.activate(locale)
    return next({ context: { locale, i18n } })
  },
)

4. src/start.ts — register the middleware. If the file already exists (the template sometimes ships it), add linguiMiddleware to the existing requestMiddleware array; if not, create it:

// src/start.ts
import { createStart } from '@tanstack/react-start'
import { linguiMiddleware } from './modules/lingui/lingui-middleware'

export const startInstance = createStart(() => ({
  requestMiddleware: [linguiMiddleware],
}))

5. src/router.tsx — getRouter() is called once per request on the server (the template already creates a fresh QueryClient per call for the same reason). Pull the per-request i18n from the start context, wrap the app in I18nProvider, and wire dehydrate/hydrate so the client first paint matches the server exactly:

// src/router.tsx
import { setupI18n, type I18n } from '@lingui/core'
import { I18nProvider } from '@lingui/react'
import { createRouter } from '@tanstack/react-router'
import { getGlobalStartContext } from '@tanstack/react-start'
import { SOURCE_LOCALE } from './i18n'
import { routeTree } from './routeTree.gen'

export function getRouter() {
  // Server: the lingui middleware put a per-request i18n instance in the start
  // context. Client: no middleware ran — create a fresh instance; hydrate()
  // below fills it from the server's dehydrated state before first render.
  const i18n: I18n =
    getGlobalStartContext()?.i18n ??
    setupI18n({ locale: SOURCE_LOCALE, messages: { [SOURCE_LOCALE]: {} } })

  return createRouter({
    routeTree,
    context: { i18n }, // merge into the existing context object (queryClient, ...)
    Wrap: ({ children }) => <I18nProvider i18n={i18n}>{children}</I18nProvider>,
    dehydrate: () => ({
      locale: i18n.locale,
      messages: i18n.messages, // catalog for the active locale
    }),
    hydrate: (dehydrated) => {
      i18n.loadAndActivate({ locale: dehydrated.locale, messages: dehydrated.messages })
    },
  })
}

Keep everything already in getRouter() — the QueryClient, existing context entries, defaultPreload, etc. Only add the i18n pieces.

API drift warning: getGlobalStartContext has been moving between @tanstack/react-start versions. If the import doesn't exist in the installed version, check how the installed @tanstack/react-start exposes the request-scoped start context (the export name and location have changed across releases) and adapt this one line — the rest of the pattern is unchanged. The ?.i18n access also requires the middleware's context type to be registered with Start's type system (the createStart registration in step 4); if TypeScript complains about the property, check how the installed version registers request-middleware context types.

6. src/routes/__root.tsx — extend the route context type with i18n and replace the template's hardcoded <html lang="en">. The template's root route uses createRootRouteWithContext with a shellComponent (RootDocument); Wrap from step 5 renders above the shell, so useLingui() works here:

// src/routes/__root.tsx (i18n-relevant parts — keep everything else in the file)
import type { I18n } from '@lingui/core'
import { useLingui } from '@lingui/react/macro'
import { createRootRouteWithContext, HeadContent, Scripts } from '@tanstack/react-router'
import { getDirection } from '@/i18n'

// Add `i18n` to the EXISTING context type — e.g. if the template already has
// { queryClient: QueryClient }, it becomes { queryClient: QueryClient; i18n: I18n }
export const Route = createRootRouteWithContext<{ i18n: I18n }>()({
  shellComponent: RootDocument,
})

function RootDocument({ children }: { children: React.ReactNode }) {
  const { i18n } = useLingui()
  return (
    <html lang={i18n.locale} dir={getDirection(i18n.locale)}>
      <head>
        <HeadContent />
      </head>
      <body>
        {children}
        <Scripts />
      </body>
    </html>
  )
}

Because the server resolved the locale before rendering, the HTML arrives already translated with the correct lang and dir — no client-side correction, no flash.

Do not localize head() / meta titles yet. Putting translated strings in a route's head() triggers a known TanStack Router hydration bug (issue #4279) that duplicates head content. Leave route titles and meta descriptions in the source language for now; localize body content only.

B5. Scaffold the catalogs

Same as Path A — create src/locales/{locale}/messages.po for every locale exactly as in A7 (valid PO header, Language: and Plural-Forms per locale, source locale included).

B6. Routing: cookie-based by default

The default flow keeps URLs untouched — the locale lives in the cookie, and every URL serves the visitor's language. No route changes, no link rewriting.

A URL-prefix variant (/es/dashboard via an src/routes/$locale/ layout route that validates the param and activates that locale's catalog) exists and matters more under SSR than in a SPA — per-language URLs are crawlable and indexable. It's out of scope for the default flow; mention it to the user as a future option if they ask about SEO for translated pages.

B7. Language switcher

Two files. The switcher calls a server function that sets the locale cookie, then does a full reload so the server re-renders everything under the new cookie — simple and correct, since i18n state is per-request.

Critical file-split rule: a file that defines createServerFn must not also use Lingui macros — the macro transform and the server-function extraction conflict and break the build. Keep the server function in its own macro-free file. Inside any server-function handler that needs translated text, use i18n._(msg`...`) with the request's i18n instance, which arrives via the request-middleware context — e.g. handler(async ({ context }) => context.i18n._(msg`Saved`)) — never bare t macros.

1. src/modules/lingui/locale-fn.ts — the server function (no macros in this file):

// src/modules/lingui/locale-fn.ts
// No Lingui macros in this file — see the file-split rule above.
import { createServerFn } from '@tanstack/react-start'
import { setResponseHeader } from '@tanstack/react-start/server'
import { LOCALES } from '@/i18n'

export const setLocaleServerFn = createServerFn({ method: 'POST' })
  .inputValidator((locale: string) => {
    if (!LOCALES.includes(locale)) throw new Error(`Unsupported locale: ${locale}`)
    return locale
  })
  .handler(async ({ data: locale }) => {
    setResponseHeader(
      'Set-Cookie',
      `locale=${locale}; Path=/; Max-Age=31536000; SameSite=Lax; Secure`,
    )
  })

(Older Start versions name the validator step .validator() instead of .inputValidator() — match what the installed @tanstack/react-start exports.)

2. src/components/LanguageSwitcher.tsx — shadcn Select, same look as Path A's:

// src/components/LanguageSwitcher.tsx
import { useLingui } from '@lingui/react/macro'
import {
  Select,
  SelectContent,
  SelectItem,
  SelectTrigger,
  SelectValue,
} from '@/components/ui/select'
import { LOCALES } from '@/i18n'
import { setLocaleServerFn } from '@/modules/lingui/locale-fn'

export function LanguageSwitcher() {
  const { i18n } = useLingui()
  const displayNames = new Intl.DisplayNames([i18n.locale], { type: 'language' })

  async function switchLocale(locale: string) {
    await setLocaleServerFn({ data: locale })
    // Full reload: the server re-renders with the new cookie, so SSR output,
    // hydration state, and <html lang/dir> all change together.
    window.location.reload()
  }

  return (
    <Select value={i18n.locale} onValueChange={switchLocale}>
      <SelectTrigger className="w-[140px]">
        <SelectValue />
      </SelectTrigger>
      <SelectContent>
        {LOCALES.map((locale) => (
          <SelectItem key={locale} value={locale}>
            {displayNames.of(locale) ?? locale}
          </SelectItem>
        ))}
      </SelectContent>
    </Select>
  )
}

Place it in the app's existing header or navigation, matching the surrounding styling.

B8. Verify via the preview

1. The preview builds with no errors. A build break right after adding a server function almost always means macros and createServerFn ended up in the same file — re-check the B7 file split.
2. First paint is already localized. With a non-source accept-language (or the cookie set), the page arrives in that language with no flash of source-language content.
3. Switching locale round-trips. Pick a language in the switcher: the locale cookie is set, the page reloads, and the new locale renders.
4. <html lang> is correct in view-source. The server-rendered HTML (not just the live DOM) carries the right lang and dir — that's the SSR proof.

Tell the user what to expect: the plumbing is live, but visible text doesn't change until strings are wrapped (Phase 4) and translations arrive (Phase 6).

---

Phase 3: Add the coding rules to AGENTS.md

Setup makes translation possible; this phase makes it stick. Every future edit to this project — by you, in any later chat — must keep new strings wrapped and catalogs updated. Write the rules below into the repo-root AGENTS.md so they're always in force.

Mechanics:

• If AGENTS.md doesn't exist, create it containing exactly the block below.
• If it exists, append the block at the end.
• The block is wrapped in <!-- lovable-i18n:rules:start --> / <!-- lovable-i18n:rules:end --> markers. If those markers already exist in the file, replace everything between them and keep the marker lines themselves — this makes re-running the skill safe.
• Substitute the real source locale for en in the catalog-upkeep section if it differs.

Write this block (everything between and including the markers):

<!-- lovable-i18n:rules:start -->
# i18n coding rules (Lingui)

This app is localized with Lingui. Every user-visible string must be wrapped in a Lingui macro, and every NEW string must also be added to the PO catalogs (see "Catalog upkeep" below). Apply these rules to every edit.

## Picking the right macro

```
Does the wording change with a number ("1 item" / "3 items")?
  YES → <Plural> in JSX, or useLingui()'s t`{count, plural, one {...} other {...}}` elsewhere

Is the text rendered in JSX?
  YES → <Trans>text</Trans>

Is it a prop/attribute value (placeholder, aria-label, title, alt) or a string
built in an event handler (toast message)?
  YES → const { t } = useLingui()  then  t`text`

Is it defined outside a component (constant, config object, array)?
  YES → msg`text` to define; resolve with t(descriptor) inside the component

Is it inside a TanStack Start server-function handler?
  YES → i18n._(msg`text`) with the request's i18n instance — never bare t
```

Imports: JSX macros (`Trans`, `Plural`, `Select`) and `useLingui` come from `@lingui/react/macro`; `msg` and `ph` come from `@lingui/core/macro`. The only `t` you use is the one returned by `useLingui()` — never import `t` from `@lingui/core/macro` (it binds a global i18n instance this app doesn't load), and never import from the deprecated `@lingui/macro`.

## Patterns

JSX text:

```tsx
import { Trans } from '@lingui/react/macro'
<h1><Trans>Dashboard</Trans></h1>
```

Props, attributes, and event-handler strings:

```tsx
import { useLingui } from '@lingui/react/macro'
function Field() {
  const { t } = useLingui()
  return <input placeholder={t`Search...`} aria-label={t`Search`} />
}
// In handlers: toast.success(t`Changes saved`)
```

Module-scope constants — `msg` defines, `t(descriptor)` resolves at render. There is no `t` at module scope (`useLingui()` only works inside a component) — never reach for a module-level `t` import to work around that; use `msg`:

```tsx
import { msg } from '@lingui/core/macro'
const navItems = [{ label: msg`Home`, href: '/' }]
// in the component: const { t } = useLingui(); ... {t(item.label)}
```

Interpolation: only a bare variable (`${name}`) auto-names its placeholder. Any other expression (`user.name`, a function call) extracts as `{0}`, meaningless to translators — name it with `ph()`:

```tsx
import { ph } from '@lingui/core/macro'
t`Total: ${ph({ total: i18n.number(amount) })}`   // → "Total: {total}", not "{0}"
```

## Plurals

```tsx
<Plural value={count} one="# item" other="# items" />
// non-JSX (t from useLingui()): t`{count, plural, one {# item} other {# items}}`
```

- `other` is always required — it's the fallback for every language.
- `#` is the count placeholder; don't repeat the variable name.
- Categories are CLDR: `zero`, `one`, `two`, `few`, `many`, `other`.
- Never build plurals with a ternary between two separate strings — that bakes English plural rules into the code.
- `value` must be a number.

## Numbers and dates

Use `i18n.number()` and `i18n.date()` (from `useLingui()`) — never hand-rolled formatting. Flag for review any `toFixed()`, `"$" + price` concatenation, or hardcoded date patterns like `"MM/DD/YYYY"`.

## What not to wrap

CSS class names, `console.log`/debug strings, import paths, object keys and internal codes, `ALL_CAPS` enum/variant values, `data-testid` attributes, URL strings and API paths, code identifiers.

## Translator comments

Add a comment when the string is ambiguous without seeing the UI:

- 1–2 word strings with multiple possible readings ("Home", "Track").
- Action labels without a visible object ("Remove" — remove what?).
- Placeholders whose meaning isn't obvious (`{count} remaining` — remaining what?).
- Domain-specific terms whose meaning depends on this app's domain.

Syntax: `<Trans comment="Main nav link, not the building">Home</Trans>`, `t({ message: 'Clear', comment: 'Clear search input' })`, `msg({ message: 'Save', comment: 'Save document button' })`. Describe where the string appears and what it refers to (not what the word means); keep it under 80 characters.

Use `context` (not `comment`) when the **same text needs different translations** in different places — it splits the catalog entry: `<Trans context="direction">Right</Trans>` vs `<Trans context="correctness">Right</Trans>`.

## Catalog upkeep (this project's workflow)

- Every NEW user-visible string must be wrapped AND appended as an entry to **every** `src/locales/*/messages.po` file — including the source-locale (`en`) file. `msgid` is the exact source text (or full ICU expression); `msgstr` stays **empty** in all files (do not copy the msgid into msgstr — Lingui falls back to the source text at runtime).
- Never run lingui CLI commands (`extract`, `compile`) — there is no terminal here; a GitHub Actions workflow runs extraction.
- Never modify `#.` or `#:` comment lines on existing `.po` entries — extraction regenerates them (you do write them when appending a NEW entry). Translator comments belong in code, via `comment=`.
- When adding a new locale: update `locales` in `lingui.config.ts`, update `LOCALES` in `src/i18n.ts`, and scaffold `src/locales/<locale>/messages.po` with a valid PO header.
<!-- lovable-i18n:rules:end -->

After writing the file, tell the user in one sentence that the coding rules are now in AGENTS.md, so future edits in any chat will keep new text translatable.

---

Phase 4: Wrap existing strings

The app's existing hardcoded text becomes translatable here. Apply the Phase 3 rules (they're in AGENTS.md now — they bind you too); this phase adds the conversion-specific workflow on top.

For every string you wrap, add the matching entry to every catalog file per the PO catalog maintenance protocol below. Wrapping without the catalog entry means the string can never receive a translation until CI runs; do both in the same edit.

Work order

1. App shell and navigation first — header, sidebar, footer, nav data. These appear on every page, so they pay off immediately.
2. Shared components — buttons, dialogs, empty states, form fields used across pages.
3. Pages/routes — one page at a time, top of the route tree downward.

Work file by file, and after each batch of a few files, confirm the preview still builds before continuing. A macro typo discovered three files later is much harder to locate.

What counts as user-visible

Wrap: JSX text, placeholders, aria-label / title / alt attributes, button labels, toast and notification messages, validation messages, empty states, loading/error copy, confirmation dialogs, page headings. Skip: everything on the Phase 3 "what not to wrap" list. On Path B, leave route head() titles and meta strings unwrapped for now (hydration bug — see B4).

Conversion patterns

Basics — <Trans> for JSX, useLingui() + t`...` for props and handlers — are in the Phase 3 rules. The patterns below are the ones conversion work actually trips over.

Nav/sidebar data arrays. Constants at module scope can't call t — useLingui()'s t only exists inside a component. Mark with msg, resolve at render:

import { msg } from '@lingui/core/macro'
import { useLingui } from '@lingui/react/macro'
import type { MessageDescriptor } from '@lingui/core'

const sidebarItems: Array<{ label: MessageDescriptor; href: string }> = [
  { label: msg({ message: 'Dashboard', comment: 'Main navigation sidebar' }), href: '/' },
  { label: msg`Users`, href: '/users' },
  { label: msg`Settings`, href: '/settings' },
]

function Sidebar() {
  const { t } = useLingui()
  return (
    <nav>
      {sidebarItems.map((item) => (
        <a key={item.href} href={item.href}>{t(item.label)}</a>
      ))}
    </nav>
  )
}

The same pattern applies to copy exported from shared modules (lib/copy.ts): export MessageDescriptor values via msg, never raw strings, and resolve with t(descriptor) at the call site.

Validation messages. Schema definitions run outside render — same msg-then-resolve pattern:

import { msg } from '@lingui/core/macro'
import { useLingui } from '@lingui/react/macro'

const fieldErrors = {
  required: msg`This field is required`,
  email: msg`Enter a valid email address`,
  minLength: msg`Must be at least 8 characters`,
}

function SignUpForm() {
  const { t } = useLingui()
  function validate(value: string) {
    if (!value) return t(fieldErrors.required)
    if (value.length < 8) return t(fieldErrors.minLength)
    return null
  }
  // ...
}

Toasts inside handlers. Handlers close over the component's t, so plain t`...` works:

const { t } = useLingui()
async function handleSave() {
  try {
    await save()
    toast.success(t`Changes saved successfully`)
  } catch {
    toast.error(t`Failed to save changes. Please try again.`)
  }
}

Hand-rolled formatting. Replace "$" + price, toFixed(), and date-string concatenation with the locale-aware helpers:

const { i18n } = useLingui()
<span>{i18n.number(amount, { style: 'currency', currency: 'USD' })}</span>
<time>{i18n.date(new Date(timestamp), { dateStyle: 'medium' })}</time>

Count-dependent strings. Anything like `${items.length} results` is a plural, even when the English happens to look fine — convert to <Plural> / ICU per the Phase 3 rules, and put the full ICU expression in the catalog msgid.

Path B server functions. Inside createServerFn handlers, use i18n._(msg`...`) with the request's i18n instance, and keep macros out of files that define server functions (B7 rule).

Translator comments — now, not later

This is the moment the Phase 3 comment rules bite: while wrapping, you're looking at each string in its UI context, which is exactly what the comment must capture. Run the ambiguity check (short strings, bare action labels, unclear placeholders, domain terms) on every wrap and add comment= inline. The comments flow into the .po files via CI extraction and reach translators through Globalize.

End-of-phase verification

1. The preview builds with no macro or import errors.
2. Spot-check key pages — nothing renders as a raw descriptor object, {0}, or unprocessed ICU text.
3. Switch locale — strings still show source text (translations don't exist yet; that's Phase 6), with no console errors about catalog imports.
4. Hunt for stragglers — scan components for remaining string literals in JSX text positions and in placeholder= / aria-label= / title= / alt= attributes; wrap what you find.
5. Catalog parity — every wrapped string has an entry in every src/locales/*/messages.po.

Tell the user what changed: how many files were converted, and that the app is now fully translatable but still shows source-language text until translations arrive.

---

PO catalog maintenance protocol

Until the CI workflow (Phase 5) takes over, you maintain the .po files by hand. Follow this protocol exactly so your entries match what lingui extract produces — then CI's first run normalizes rather than fights your work.

Entry shape

This is exactly what lingui extract writes with this project's config (lineNumbers: false in A3 keeps #: references to file paths only — no line numbers); match it:

#. A translator comment from the comment= prop
#: src/components/Header.tsx
msgid "Welcome back, {name}!"
msgstr ""

• #. line: only when the code has a comment= for this string.
• #: line: the source file path where the string lives.
• msgid: the exact source text — including placeholder names ({name}) exactly as the macro produces them.
• msgstr: empty (see below).
• One blank line between entries.
• When the code uses context=, add msgctxt "the context value" on its own line directly above msgid.

Plural and other ICU strings put the full ICU expression in the msgid:

#: src/components/CartBadge.tsx
msgid "{count, plural, one {# item} other {# items}}"
msgstr ""

Rules

• Every locale gets the entry — including the source locale. All with msgstr "". Lingui falls back to the source text (the msgid) at runtime for any missing message, so empty msgstr renders correctly in the source locale and signals "untranslated" to the translation platform for the targets. Never copy the msgid into msgstr.
• Append-only. Add new entries at the end of each file. Never reorder existing entries, never rewrite #. / #: lines on entries you didn't author, never reformat the file.
• Formatting is CI-owned after the first CI run. Extraction regenerates #: references and #. comments from code, adds missing entries, removes entries whose source strings are gone (--clean), and normalizes ordering — while preserving existing msgstr translations. Any hand-decoration you add beyond the shape above will be erased; any translation in msgstr survives.

"Translate it now"

If the user asks for translations before Globalize is connected, you may fill the target-locale msgstr values yourself — but tell the user these are machine-draft translations, unreviewed, and that Globalize will manage real translations once connected (Phase 6). Drafts in msgstr survive CI extraction and get superseded by platform translations later.

Sync conflicts

If Lovable reports a GitHub sync conflict on a .po file (you and CI/Globalize edited it simultaneously), take the remote version — CI and Globalize are the catalog authorities — then re-apply only the entries of yours that are missing from it.

---

Phase 5: CI — catalog extraction workflow

Only if the user opted in during Ask. GitHub is already connected — the prerequisite gate guaranteed it before any setup ran — so the workflow file syncs to the repo and CI can run.

This workflow is what retires the hand-maintenance protocol: after every code push, it runs lingui extract and commits the normalized catalogs back. You keep adding entries by hand only as a same-edit courtesy (so strings are immediately visible to translators); CI is the authority that fixes anything you got slightly wrong.

Create .github/workflows/i18n-extract.yml:

name: i18n-extract
on:
  push:
    branches: [main]
    paths:
      - 'src/**'
      - 'lingui.config.*'
      - '!src/locales/**'
permissions:
  contents: write
concurrency:
  group: i18n-extract
  cancel-in-progress: true
jobs:
  extract:
    if: github.actor != 'github-actions[bot]'
    runs-on: ubuntu-latest
    steps:
      - uses: actions/checkout@v4
      - uses: actions/setup-node@v4
        with:
          node-version: 24   # Lingui 6 is ESM-only and needs Node >= 22.19
      - run: npm ci
      - run: npx lingui extract --clean
      - name: Commit catalog updates
        run: |
          git config user.name "github-actions[bot]"
          git config user.email "github-actions[bot]@users.noreply.github.com"
          git add src/locales
          git diff --staged --quiet || (git commit -m "chore(i18n): sync message catalogs [skip ci]" && git push)

If the project's default branch isn't main, adjust branches: to match — Lovable syncs with the default branch.

If the run fails at npm ci — missing or out-of-sync lockfile — switch that step to npm install --no-audit --no-fund; if the repo ships bun.lockb or pnpm-lock.yaml, use the matching setup action and install command instead.

If the workflow file fails to sync to GitHub: Lovable's GitHub App may lack the workflows permission, and GitHub rejects pushes that create workflow files without it. In that case, give the user the file path and the full YAML above and ask them to add it via the GitHub web UI (repo → Add file → paste). Everything else proceeds normally.

Why it's shaped this way

• No compile step, ever. @lingui/vite-plugin compiles .po catalogs during the app build — there is nothing for CI to compile, only extraction to run.
• Loop prevention is three-layer. The commit-back could re-trigger the workflow forever; three independent guards stop that: (1) pushes made with the default GITHUB_TOKEN don't trigger on: push workflows at all; (2) the !src/locales/** path filter ignores catalog-only pushes — which also keeps Globalize's translation deliveries from triggering extraction; (3) belt-and-braces, the [skip ci] commit tag and the github.actor guard.
• concurrency prevents racing pushes. Two quick Lovable syncs would otherwise run two extractions that both try to push; the group cancels the stale one.
• The round-trip is fast. Lovable auto-commits your edit and syncs it to GitHub → the workflow extracts and normalizes the catalogs → the commit-back lands on the default branch → Lovable's two-way sync pulls it into the project within seconds. From then on, treat catalog formatting as CI-owned (see the PO protocol).

Verify with the user after the next code push: the i18n-extract run shows up in the repo's Actions tab, and a chore(i18n): sync message catalogs commit appears and flows back into Lovable.

---

Phase 6: Connect Globalize.now

Connect Globalize unless the user opted out in the Ask phase — it's on by default. The best path is the Globalize MCP connector: once it's added to this Lovable project, you create the project and link the repo yourself, right here in the chat. If the user won't add the connector, fall back to the paste-ready dashboard / CLI steps below.

GitHub is already connected (the prerequisite), so your catalogs already live in a repo Globalize can reach — connecting Globalize just points it at that same repo.

Print this connection summary (with the project's real values):

Globalize.now connection details

• Project name: <repo name> (suggestion)
• Source language: en
• Target languages: es, fr
• Catalog pattern: src/locales/{locale}/messages.po
• File format: po

Primary path — the Globalize MCP connector

Lovable can talk to Globalize through a hosted MCP server, so you can create the project and link the repo directly from this chat — no leaving Lovable.

1. Check whether you already have Globalize tools. If your connectors already expose Globalize tools (projects, languages, github, repositories), the connector is set up — skip to step 3.

2. Otherwise, walk the user through the one-time connector setup:

   Connect Globalize once so I can set it up from here:

   1. Open Connectors → Chat connectors → New MCP server.
   2. Name: Globalize
   3. Server URL: https://api.globalize.now/mcp
   4. Authentication: choose Bearer token / API key and paste your key from https://app.globalize.now/settings/api-keys.
   5. Click Add server, then tell me to continue.

   Wait for the user to confirm the connector is added, then continue.

3. Create the project and connect the repo using the Globalize MCP tools. They mirror the @globalize-now/cli-client command groups — use whatever tool names your connector exposes; don't assume exact signatures. Report each step in the chat as you go:

   • List languages and match the source/target locale IDs (mirrors languages list).
   • Create the project with the suggested name and those language IDs (mirrors projects create).
   • Install the Globalize GitHub App — this is separate from Lovable's GitHub connection. The tool returns an install URL; ask the user to approve it in the browser, then read back the installation and note its UUID (mirrors github install → github installations).
   • Connect the repository with the catalog pattern [{"pattern": "src/locales/{locale}/messages.po", "fileFormat": "po"}] (mirrors repositories create).
   • Optionally confirm detection (mirrors repositories detect).

   Once the repo is connected, you're done — jump to Close the loop below.

Fallback path — no MCP (dashboard or local CLI)

If the user would rather not connect the MCP, these steps happen outside this chat, on the Globalize dashboard or the user's machine — print everything ready to paste.

Option 1 — Globalize.now dashboard (no tooling needed). On globalize.now: create a project with those source/target languages, connect the same GitHub repository Lovable syncs to (this installs the Globalize GitHub App — approve it in the browser; translation deliveries then flow back into Lovable through that repo), and set the catalog pattern and file format above.

Option 2 — Globalize CLI on the user's machine (requires Node.js). Give the user this sequence to run locally:

# 1. Sign in (opens the browser for device authorization)
npx @globalize-now/cli-client auth login

# 2. Find the language IDs for your locales (each entry has a `locale` and an `id`)
npx @globalize-now/cli-client languages list --json

# 3. Create the project with those IDs
npx @globalize-now/cli-client projects create \
  --name "<PROJECT_NAME>" \
  --source-language <SOURCE_LANGUAGE_ID> \
  --target-languages <TARGET_ID_1> <TARGET_ID_2> \
  --json

# 4. Install the Globalize GitHub App (opens the browser), then list installations
#    and note both ids: the numeric installationId and the UUID id
npx @globalize-now/cli-client github install
npx @globalize-now/cli-client github installations --json

# 5. Connect the repository with the catalog pattern (use the UUID id here)
npx @globalize-now/cli-client repositories create \
  --project-id <PROJECT_ID> \
  --git-url https://github.com/<OWNER>/<REPO>.git \
  --provider github \
  --github-installation-id <INSTALLATION_UUID> \
  --patterns '[{"pattern": "src/locales/{locale}/messages.po", "fileFormat": "po"}]' \
  --json

@globalize-now/cli-client is deliberately unpinned — the platform manages its release cadence. If the user works with a local coding agent (Claude Code etc.), point them at the globalize-now-account-setup skill (sign in) followed by globalize-now-project-setup (create the project + connect the repo) instead — together they walk the same flow with full auto-detection.

Close the loop. Once connected, Globalize picks up the catalogs from the repo, translates new entries, and delivers translated .po files back via PRs or pushes to the default branch. Lovable's GitHub sync pulls them in, and the language switcher starts showing real translations — no action needed in this chat. The CI workflow ignores locale-only pushes (the !src/locales/** path filter), so translation deliveries never trigger extraction loops.

---

Troubleshooting

Symptom	Likely cause	Fix
Preview build error mentioning "AST schema mismatch" or "failed to invoke plugin" (Path A)	@lingui/swc-plugin compiled against a different swc_core than @vitejs/plugin-react-swc ships	Look up the compatible version at https://plugins.swc.rs and pin @lingui/swc-plugin to that exact version (no caret) — see the A1 caveat
Build fails resolving @lingui/vite-plugin, or ESM/ERR_REQUIRE_ESM-style errors from Lingui packages	The build image's Node is too old for Lingui 6 (ESM-only, needs Node ≥ 22.19)	Pin all @lingui/* packages to @^5 instead. Keep lingui.config.ts as-is — the formatter(...) form from @lingui/format-po works in v5 too
TS error Cannot find module './locales/en/messages.po'	Missing the *.po module declaration	Add the declaration from A4 (src/vite-env.d.ts or src/po-modules.d.ts)
Strings render as raw ICU ({count, plural, ...}) or stay in the source language after switching	Catalog not loaded for that locale (typo in the dynamic import path, missing .po file) or the entry is missing from that locale's catalog	Check the src/locales/<locale>/messages.po file exists with a valid header (A7) and contains the entry (PO protocol)
<Trans> renders as literal macro output, but the build succeeds (Path A)	SWC plugin registered as a bare string instead of the ['@lingui/swc-plugin', {}] tuple	Use the tuple shape in vite.config.ts (A2)
(Path B) Build breaks right after adding a server function	Lingui macros and createServerFn in the same file	Split them: server functions in their own macro-free file; use i18n._(msg`...`) inside handlers (B7)
(Path B) Duplicated <title> / head content after hydration	Known TanStack Router issue (#4279) with localized head() strings	Don't localize head() / meta strings for now — keep them in the source language (B4)
(Path B) getGlobalStartContext not found / not exported	TanStack Start API drift between versions	Check how the installed @tanstack/react-start exposes the request-scoped start context and adapt that one line in src/router.tsx (B4)
CI workflow never runs	GitHub not connected in Lovable; the workflow file didn't sync (GitHub App lacks the workflows permission); or the default branch isn't main	Connect GitHub; add the YAML via the GitHub web UI; fix branches: in the workflow (Phase 5)
CI run fails at the install step (npm ci)	Lockfile missing or out of sync — e.g. the repo ships bun.lockb or pnpm-lock.yaml instead of package-lock.json, or the lockfile lags the added dependencies	Switch the step to npm install --no-audit --no-fund, or use the setup action + install command matching the repo's lockfile (Phase 5)
CI commits catalog updates but Lovable doesn't show them	Lovable's sync follows the default branch only	Confirm the workflow pushed to the default branch (check the Actions log and the branch of the chore(i18n) commit)
Globalize tools not available after adding the connector (Phase 6)	Wrong URL, missing/invalid API key, or the connector was added but this chat turn predates it	Verify the URL is exactly https://api.globalize.now/mcp, re-check the key at app.globalize.now/settings/api-keys, then reference the Globalize connector again
Globalize's GitHub App install looks redundant with Lovable's GitHub	Globalize installs its own GitHub App, separate from Lovable's GitHub connection	Have the user approve the Globalize GitHub App in the browser when the connect step (MCP github install, or the dashboard) triggers it — Lovable's own GitHub link doesn't cover it