JQuery on change hitting default

I am trying to dynamically load content with select.

$(document).ready(function () {
    $("#lang").on("change", function () {
        switch(this.value) {
            case "pl":
                $("#content").load("pl.html");
            case "en":
                $("#content").load("en.html");
            default:
                alert("default")
        }
    });
});

<select name="lang" id="lang">
    <option value="en">en</option>
    <option value="pl">pl</option>
</select>
<div id="content"></div>

Whenever I am changing value the default alert is occurring and the content is not always updated properly.

If break is omitted, execution will proceed to the next case clause, even to the default clause, regardless of whether the value of that clause matches.

enter link description here

<!-- begin snippet: js hide: false console: true babel: false -->

<!-- language: lang-js -->

$(document).ready(function() {
  $("#lang").on("change", function() {
    switch (this.value) {
      case "pl":
        $("#content").load("pl.html");
        break;
      case "en":
        $("#content").load("en.html");
        break;
      default:
        alert("default")
        break;
    }
  });
});

<!-- language: lang-html -->

<script src="https://cdnjs.cloudflare.com/ajax/libs/jquery/3.3.1/jquery.min.js"></script>
<select name="lang" id="lang">
  <option value="en">en</option>
  <option value="pl">pl</option>
</select>
<div id="content"></div>

<!-- end snippet -->