We can set the language given by the navigator's user.

server.js

-const port = 9000;
+const port = 9001;
 const browserSyncPort = 3000;
 const distPath = 'www';
+const fs = require('fs')
+const path = require('path')
 
 // express server
 const { join } = require('path');
 const express = require('express');
 const app = express();
+
+const default_lang = 'en'
+
+function parseLanguageData(stringData) {
+  var arrayData = stringData.split(',').map(element => 
+    element.split(/[-;]/).shift()
+  );
+  arrayData.push(default_lang)
+  return arrayData
+}
+
+function getAvailableLanguage() {
+  const langs = fs.readdirSync(distPath)
+  .filter(f => path.basename(f, '.yml').match(/^index-[a-z]{2}\.html/))
+  .map(f => f.match(/^index-([a-z]{2})\.html/)[1])
+  return langs
+}
+
+function matchLanguage(availableLanguages, userLanguages) {
+  for (let index = 0; index < userLanguages.length; index++) {
+    const userLanguage = userLanguages[index];
+    for (let index = 0; index < availableLanguages.length; index++) {
+      const availableLanguage = availableLanguages[index];
+      if (userLanguage === availableLanguage) {
+        return userLanguage
+      }
+    }
+  }
+}
+
 app
   .use(express.static(distPath))
   // .use('/src', express.static(join(__dirname, 'src')))
-  .get(/^[^.]*$/, (req, rep) =>
-    rep.sendFile(join(__dirname, distPath, '/index-fr.html'))
+  .get(/^[^.]*$/, (req, rep) => {
+    var langRequired = matchLanguage(getAvailableLanguage(), parseLanguageData(req.headers["accept-language"]))
+    console.log('langRequired : ',  langRequired)
+    rep.sendFile(join(__dirname, distPath, `/index-${langRequired}.html`))
+  }
   )
   .listen(port);