KevinK.dev.js/src/server/languageRedirect.js

/* eslint-disable no-undef */
const config = require("../../config");
const locale = require("locale");

let supported = new locale.Locales(config.languages);
let defaultLang = "en";

export default ({ Router }) => {
    Router.on("*", checkLang);
};

async function checkLang({ request }) {
    const { url } = request

    // eslint-disable-next-line no-undef
    let requestURL = new URL(url);

    if (requestURL.pathname.startsWith("/assets") ||
        requestURL.pathname.startsWith("/icons") ||
        requestURL.pathname.startsWith("/manifest.webmanifest") ||
        requestURL.pathname.startsWith("/favicon") ||
        requestURL.pathname.startsWith("/sw.js") ||
        requestURL.pathname.startsWith("/api")) {

        return;
    }

    for (let i = 0; i < config.languages.length; i++) {
        const language = config.languages[i];

        if (requestURL.pathname.startsWith("/" + language)) {
            return;
        }
    }

    let headers = request.headers;

    let selectedLanguage = defaultLang;

    if (headers.has("Accept-Language")) {
        let languageHeader = headers.get("Accept-Language");

        let requestLocales = new locale.Locales(languageHeader);

        selectedLanguage = requestLocales.best(supported);
    }

    requestURL.pathname = "/" + selectedLanguage + requestURL.pathname;

    ///return Response.redirect(requestURL.toString(), 302);

    return new Response(null, {
        status: 302,
        headers: {
            Location: requestURL.toString(),
        },
    });
}