Migrate I18next To Lingui

- [ ] Step 1: Install Lingui packages
- [ ] Step 2: Create lingui.config.js
- [ ] Step 3: Set up build tooling (Babel/SWC/Vite)
- [ ] Step 4: Replace i18n initialization
- [ ] Step 5: Migrate React components (useTranslation → useLingui, Trans → Trans)
- [ ] Step 6: Migrate JS/TS strings (t() → t``)
- [ ] Step 7: Migrate plurals
- [ ] Step 8: Migrate namespaces
- [ ] Step 9: Convert existing translation catalogs
- [ ] Step 10: Run lingui extract && lingui compile
- [ ] Step 11: Remove i18next packages

# Core (always required)
npm install @lingui/core @lingui/react

# CLI (dev)
npm install --save-dev @lingui/cli

# Macro support - pick one based on build tool:
# Babel
npm install --save-dev @lingui/babel-plugin-lingui-macro
# SWC
npm install --save-dev @lingui/swc-plugin
# Vite (also install the Babel macro plugin above — see Step 3)
npm install --save-dev @lingui/vite-plugin

import { defineConfig } from "@lingui/cli";

export default defineConfig({
  sourceLocale: "en",
  locales: ["en", "de", "fr"], // match your existing locales
  catalogs: [
    {
      path: "<rootDir>/src/locales/{locale}/messages",
      include: ["src"],
    },
  ],
});

import { lingui } from "@lingui/vite-plugin";
import react from "@vitejs/plugin-react";

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

// Dynamic import; the .po extension is mandatory
const { messages } = await import(`./locales/${locale}/messages.po`);

// src/vite-env.d.ts
declare module "*.po" {
  import type { Messages } from "@lingui/core";
  export const messages: Messages;
}

{ "plugins": ["macros"] }

module.exports = {
  experimental: {
    swcPlugins: [["@lingui/swc-plugin", {}]],
  },
};

import i18next from "i18next";
import { initReactI18next } from "react-i18next";

i18next.use(initReactI18next).init({
  lng: "en",
  resources: { en: { translation: { key: "Hello world" } } },
});

import { i18n } from "@lingui/core";
import { I18nProvider } from "@lingui/react";
import { messages } from "./locales/en/messages";

i18n.load("en", messages);
i18n.activate("en");

function App() {
  return <I18nProvider i18n={i18n}>{/* app */}</I18nProvider>;
}

async function changeLocale(locale) {
  const { messages } = await import(`./locales/${locale}/messages`);
  i18n.load(locale, messages);
  i18n.activate(locale);
}

import { useTranslation } from "react-i18next";

function MyComponent() {
  const { t } = useTranslation();
  return <p>{t("greeting")}</p>;
}

import { useLingui } from "@lingui/react/macro";

function MyComponent() {
  const { t } = useLingui();
  return <p>{t`Hello World`}</p>;
}

import { Trans } from "react-i18next";

<Trans i18nKey="welcome">Hello World!</Trans>

import { Trans } from "@lingui/react/macro";

<Trans>Hello World!</Trans>

<Trans id="welcome">Hello World!</Trans>

<Trans i18nKey="greeting" values={{ name }}>Hello {{ name }}!</Trans>

<Trans>Hello {name}!</Trans>

import i18next from "i18next";

const msg = i18next.t("greeting", { name: "Tom" });

import { useLingui } from "@lingui/react/macro";

function MyComponent() {
  const { t } = useLingui();
  const msg = t`Hello ${name}`;
}

import { t } from "@lingui/core/macro";

const msg = t`Hello ${name}`;

import { t } from "@lingui/core/macro";

// i18next: t('navigation.home')
const msg = t({ id: "navigation.home", message: "Home" });

const LABELS = {
  active: "Active",
  inactive: "Inactive",
};
// translated at render time

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

const LABELS = {
  active: msg`Active`,
  inactive: msg`Inactive`,
};

function StatusDisplay({ status }) {
  const { _ } = useLingui();
  return <div>{_(LABELS[status])}</div>;
}

{
  "item_one": "{{count}} item",
  "item_other": "{{count}} items"
}

t("item", { count });

import { Plural } from "@lingui/react/macro";

<Plural value={count} one="# item" other="# items" />

import { plural } from "@lingui/core/macro";

const msg = plural(count, {
  one: "# item",
  other: "# items",
});

<Plural
  value={count}
  _0="No items"
  one="# item"
  other="# items"
/>

// lingui.config.js
catalogs: [
  {
    path: "<rootDir>/src/locales/{locale}/common",
    include: ["src/components/common"],
  },
  {
    path: "<rootDir>/src/locales/{locale}/auth",
    include: ["src/components/auth"],
  },
]

import { messages as commonMessages } from "./locales/en/common";
import { messages as authMessages } from "./locales/en/auth";

i18n.load("en", { ...commonMessages, ...authMessages });
i18n.activate("en");

npx lingui extract --clean   # extracts all messages → .po files, drops obsolete entries
npx lingui compile           # compiles .po → runtime message catalogs
npx tsc --noEmit             # type errors from changed imports/APIs
npm run build                # macro transform actually runs in the real build

{
  "scripts": {
    "i18n:extract": "lingui extract",
    "i18n:compile": "lingui compile"
  }
}

npx lingui compile --typescript