The Complete Guide to Next.js Internationalization

// middleware.ts  <- Must be in project ROOT, not src/
import createMiddleware from 'next-intl/middleware';
import { routing } from './src/i18n/routing';

export default createMiddleware(routing);

export const config = {
  matcher: ['/((?!api|_next|.*\\..*).*)'],
};

// app/[locale]/layout.tsx
import { routing } from '@/i18n/routing';

export function generateStaticParams() {
  return routing.locales.map((locale) => ({ locale }));
}

// app/[locale]/layout.tsx
import { NextIntlClientProvider } from 'next-intl';
import { getMessages, setRequestLocale } from 'next-intl/server';
import { routing } from '@/i18n/routing';
import { notFound } from 'next/navigation';

export function generateStaticParams() {
  return routing.locales.map((locale) => ({ locale }));
}

export default async function LocaleLayout({
  children,
  params,
}: {
  children: React.ReactNode;
  params: { locale: string };
}) {
  const { locale } = await params;
  if (!routing.locales.includes(locale as any)) notFound();

  setRequestLocale(locale);
  const messages = await getMessages();

  return (
    <html lang={locale}>
      <body>
        <NextIntlClientProvider locale={locale} messages={messages}>
          {children}
        </NextIntlClientProvider>
      </body>
    </html>
  );
}

// Server Component (default)
import { getTranslations, setRequestLocale } from 'next-intl/server';

export default async function AboutPage({
  params,
}: { params: { locale: string } }) {
  const { locale } = await params;
  setRequestLocale(locale);
  const t = await getTranslations('AboutPage');

  return <h1>{t('title')}</h1>;
}

// Client Component ('use client')
'use client';
import { useTranslations } from 'next-intl';

export default function SearchBar() {
  const t = useTranslations('SearchBar');
  return <input placeholder={t('placeholder')} />;
}

// app/[locale]/layout.tsx or any page.tsx
import { getTranslations } from 'next-intl/server';
import { routing } from '@/i18n/routing';

export async function generateMetadata({
  params,
}: { params: { locale: string } }) {
  const { locale } = await params;
  const t = await getTranslations({ locale, namespace: 'Metadata' });

  return {
    title: t('title'),
    description: t('description'),
    alternates: {
      languages: Object.fromEntries(
        routing.locales.map((l) => [l, `/${l}`])
      ),
    },
  };
}

// app/[locale]/error.tsx
'use client';
import { useTranslations } from 'next-intl';

export default function Error() {
  const t = useTranslations('Error');
  return (
    <div>
      <h1>{t('title')}</h1>
      <p>{t('description')}</p>
    </div>
  );
}

// app/not-found.tsx (root level -- needs own provider)
import { routing } from '@/i18n/routing';

export default async function GlobalNotFound() {
  return (
    <html lang={routing.defaultLocale}>
      <body>
        <h1>404 - Page Not Found</h1>
      </body>
    </html>
  );
}

# In your IDE, ask your AI assistant:
> Translate messages/en.json to German, Japanese, and Spanish

✓ messages/de.json created (1.1s)
✓ messages/ja.json created (1.4s)
✓ messages/es.json created (1.0s)