Adding Language Selector to my website but facing a problem

I am building a website that has English and Macedonian but the problem is, when I click in "MK" it changes to the Macedonian version of my website but the selector stays on EN and if I wanted to switch back to English I couldn’t the selector becomes useless. What is the problem that I can’t find? Here is the code for html and js.

`<header>
    <nav>
      <center>
        <ul class="nav-links">
          <li><a href="/">Home</a></li>
          <li><a href="contact.html">Contact</a></li>
          <li><a href="about.html">About</a></li>
          <li>
            <select id="language-selector">
              <option value="en">EN</option>
              <option value="mk">MK</option>
            </select>
          </li>
        </ul>
      </center>
    </nav>
  </header>



  <script>
    const langSelector = document.querySelector('#language-selector');
    
    langSelector.addEventListener('change', function() {
      let lang = this.value;
      
      let url = window.location.href;
      let newUrl;
      
      if (lang === 'mk') {
        newUrl = url.replace(/(index.html)$/, 'mk/home-mk.html');
      } else {
        newUrl = url.replace(/(mk\/home-mk.html)$/, 'index.html');
      }
      
      window.location.href = newUrl;
    });
  </script>`

I tried everything that came to my mind I even changed the whole js but I can’t seem to figure it out.

>Solution :

Add the selected attribute for the MK option on the mk/home-mk.html page.

<select id="language-selector">
    <option value="en">EN</option>
    <option value="mk" selected>MK</option>
</select>