In the sample app (https://github.com/JetBrains/webstorm-samples/tree/master/Express) replace routes/index.js with this file to follow the steps in the tutorial: http://blog.jetbrains.com/webstorm/2018/01/how-to-debug-with-webstorm/

index.js

var express = require("express");
var router = express.Router();

/* GET home page. */
router.get('/', function(req, res, next) {
  res.render('index', { title: 'Welcome!' });
  next()
});

router.get('/:lang', function (req, res) {
  if (req.params.lang === "de") {
    res.render('index', {title: 'Willkommen!'});
  }
  else {
    res.render('index', { title: 'Welcome!' });
  }
});

module.exports = router;