既存のVite & Reactアプリケーションを後から多言語化（i18n）する方法（2026年版ガイド）

npx intlayer extract

// 通常のReactコードを書くだけです。コンパイラが自動でテキストを抽出します
export default function App() {
  return (
    <section>
      <h1>私たちのプラットフォームへようこそ</h1>
      <p>モダンな機能を今すぐ体験してください。</p>
    </section>
  );
}

import { Dictionary } from "intlayer";

const content = {
  key: "app",
  content: {
    watashitachiNoPurattofomu: t({
      ja: "私たちのプラットフォームへようこそ",
    }),
    modannaKinoWoImasugu: t({
      ja: "モダンな機能を今すぐ体験してください。",
    }),
  },
};

export default content;

npx intlayer fill

import { Locales, type IntlayerConfig } from "intlayer";

const config: IntlayerConfig = {
  internationalization: {
    locales: [
      Locales.ENGLISH,
      Locales.FRENCH,
      Locales.SPANISH,
      Locales.JAPANESE,
    ],
    defaultLocale: Locales.JAPANESE,
  },
  ai: {
    provider: "openai",
    model: "gpt-4o-mini",
    apiKey: process.env.OPENAI_API_KEY,
    applicationContext:
      "Vite & Reactで構築された最新のSaaSアプリケーションおよび管理ダッシュボード",
  },
};

export default config;

import { Dictionary } from "intlayer";

const content = {
  key: "app",
  content: {
    watashitachiNoPurattofomu: t({
      ja: "私たちのプラットフォームへようこそ",
      en: "Welcome to our platform",
      fr: "Bienvenue sur notre plateforme",
      es: "Bienvenido a nuestra plataforma",
    }),
    modannaKinoWoImasugu: t({
      ja: "モダンな機能を今すぐ体験してください。",
      en: "Start exploring our modern features today.",
      fr: "Découvrez nos fonctionnalités modernes dès aujourd'hui.",
      es: "Comience a explorar nuestras funciones modernas hoy.",
    }),
  },
};

export default content;

npx intlayer test

import { defineConfig } from "vite";
import react from "@vitejs/plugin-react-swc";
import { intlayer } from "vite-intlayer";

export default defineConfig({
  plugins: [react(), intlayer()],
});

import { FC } from "react";
import { IntlayerProvider } from "react-intlayer";
import { MainContent } from "./MainContent";

const App: FC = () => {
  return (
    <IntlayerProvider>
      <MainContent />
    </IntlayerProvider>
  );
};

export default App;

import { FC } from "react";
import { Locales } from "intlayer";
import { useLocale } from "react-intlayer";

export const LocaleSwitcher: FC = () => {
  const { locale, setLocale, availableLocales } = useLocale();

  return (
    <select
      value={locale}
      onChange={(e) => setLocale(e.target.value as Locales)}
    >
      {availableLocales.map((loc) => (
        <option key={loc} value={loc}>
          {loc}
        </option>
      ))}
    </select>
  );
};

import fs from "fs";
import path from "path";
import { fileURLToPath } from "url";
import { generateSitemap, getMultilingualUrls } from "intlayer";

const __dirname = path.dirname(fileURLToPath(import.meta.url));
const SITE_URL = (process.env.SITE_URL || "https://example.com").replace(
  /\/$/,
  ""
);

const pathList = [
  { path: "/", changefreq: "daily", priority: 1.0 },
  { path: "/about", changefreq: "monthly", priority: 0.7 },
];

const sitemapXml = generateSitemap(pathList, { siteUrl: SITE_URL });
fs.writeFileSync(path.join(__dirname, "public", "sitemap.xml"), sitemapXml);

const getAllMultilingualUrls = (urls) =>
  urls.flatMap((url) => Object.values(getMultilingualUrls(url)));

const disallowedPaths = getAllMultilingualUrls(["/admin", "/private"]);

const robotsTxt = [
  "User-agent: *",
  "Allow: /",
  ...disallowedPaths.map((path) => `Disallow: ${path}`),
  "",
  `Sitemap: ${SITE_URL}/sitemap.xml`,
].join("\n");

fs.writeFileSync(path.join(__dirname, "public", "robots.txt"), robotsTxt);
console.log("SEOファイルが正常に生成されました。");

{
  "scripts": {
    "dev": "vite",
    "prebuild": "node generate-seo.mjs",
    "build": "vite build",
    "preview": "vite preview"
  }
}