middleware.ts

import { NextResponse, NextRequest } from 'next/server'
import { locales } from 'app/[locale]/i18n/settings'
import { fallbackLng } from 'app/[locale]/i18n/locales'

export function middleware(request: NextRequest) {
  // Check if there is any supported locale in the pathname
  const pathname = request.nextUrl.pathname

  // Check if the default locale is in the pathname
  if (pathname.startsWith(`/${fallbackLng}/`) || pathname === `/${fallbackLng}`) {
    // e.g. incoming request is /en/about
    // The new URL is now /about
    return NextResponse.redirect(
      new URL(
        pathname.replace(`/${fallbackLng}`, pathname === `/${fallbackLng}` ? '/' : ''),
        request.url
      )
    )
  }

  const pathnameIsMissingLocale = locales.every(
    (locale) => !pathname.startsWith(`/${locale}/`) && pathname !== `/${locale}`
  )

  if (pathnameIsMissingLocale) {
    // We are on the default locale
    // Rewrite so Next.js understands

    // e.g. incoming request is /about
    // Tell Next.js it should pretend it's /en/about
    return NextResponse.rewrite(new URL(`/${fallbackLng}${pathname}`, request.url))
  }
}

export const config = {
  // Do not run the middleware on the following paths
  // prettier-ignore
  matcher:
  '/((?!api|static|track|data|css|scripts|.*\\..*|_next).*|sitemap.xml)',
}