// next-i18next.config.js
module.exports = {
  i18n: {
    defaultLocale: 'en',
    locales: ['en', 'es', 'ja'],
  },
};

// next.config.js
const { i18n } = require('./next-i18next.config');

module.exports = {
  i18n,
  // ...既存の設定
};

// public/locales/en/common.json
{
  "common": {
    "save": "Save",
    "cancel": "Cancel",
    "loading": "Loading..."
  },
  "auth": {
    "login": "Log in",
    "signup": "Create account",
    "forgotPassword": "Forgot your password?"
  },
  "dashboard": {
    "welcome": "Welcome back, {{name}}",
    "items_one": "{{count}} item",
    "items_other": "{{count}} items"
  }
}

// public/locales/ja/common.json
{
  "common": {
    "save": "保存",
    "cancel": "キャンセル",
    "loading": "読み込み中..."
  },
  "auth": {
    "login": "ログイン",
    "signup": "アカウント作成",
    "forgotPassword": "パスワードをお忘れですか？"
  },
  "dashboard": {
    "welcome": "おかえりなさい、{{name}}",
    "items_one": "{{count}} 件",
    "items_other": "{{count}} 件"
  }
}

// public/locales/es/common.json
{
  "common": {
    "save": "Guardar",
    "cancel": "Cancelar",
    "loading": "Cargando..."
  },
  "auth": {
    "login": "Iniciar sesión",
    "signup": "Crear cuenta",
    "forgotPassword": "¿Olvidaste tu contraseña?"
  },
  "dashboard": {
    "welcome": "Bienvenido de nuevo, {{name}}",
    "items_one": "{{count}} elemento",
    "items_other": "{{count}} elementos"
  }
}

// pages/dashboard.tsx
import { serverSideTranslations } from 'next-i18next/serverSideTranslations';

export const getStaticProps = async ({ locale }) => ({
  props: {
    ...(await serverSideTranslations(locale, ['common'])),
  },
});

// components/LanguageSwitcher.tsx
import { useRouter } from 'next/router';

export default function LanguageSwitcher() {
  const router = useRouter();

  const switchLocale = (locale: string) => {
    router.push(router.pathname, router.asPath, { locale });
  };

  return (
    <select
      value={router.locale}
      onChange={(e) => switchLocale(e.target.value)}
    >
      <option value="en">English</option>
      <option value="es">Español</option>
      <option value="ja">日本語</option>
    </select>
  );
}