rallly/src/middleware.ts

import languageParser from "accept-language-parser";
import { NextRequest, NextResponse } from "next/server";

const supportedLocales = [
  "ca",
  "cs",
  "da",
  "de",
  "en",
  "es",
  "fi",
  "fr",
  "hu",
  "hr",
  "it",
  "ko",
  "nl",
  "pl",
  "pt-BR",
  "pt",
  "ru",
  "sk",
  "sv",
  "zh",
];

export function middleware({ headers, cookies, nextUrl }: NextRequest) {
  const newUrl = nextUrl.clone();

  // Check if locale is specified in cookie
  const localeCookie = cookies.get("NEXT_LOCALE");
  if (localeCookie && supportedLocales.includes(localeCookie.value)) {
    newUrl.pathname = `/${localeCookie.value}${newUrl.pathname}`;
    return NextResponse.rewrite(newUrl);
  } else {
    // Check if locale is specified in header
    const acceptLanguageHeader = headers.get("accept-language");

    if (acceptLanguageHeader) {
      const locale = languageParser.pick(
        supportedLocales,
        acceptLanguageHeader,
      );

      if (locale) {
        newUrl.pathname = `/${locale}${newUrl.pathname}`;
        return NextResponse.rewrite(newUrl);
      }
    }
  }

  return NextResponse.next();
}

export const config = {
  matcher: [
    "/admin/:id",
    "/demo",
    "/p/:id",
    "/profile",
    "/new",
    "/login",
    "/polls",
  ],
};