Html select menu ( without slash = google error, with slash = double slash at the end of url )

Question

I have a select menu like this

<select name="languages">
  <option value="https://www.example.com/language/en">English</option>
  <option value="https://www.example.com/language/fr">French</option>
  <option value="https://www.example.com/language/de">German</option>
  <option value="https://www.example.com/language/sp">Spanish</option>
</select>

when i select any of these links it opens correctly in the address bar, and automatically add slash at the end of the url to be like this

https://www.example.com/language/en/

but google search console see them as a Redirect errors .. i don't know why.

and if i put them like this

<select name="languages">
  <option value="https://www.example.com/language/en/">English</option>
  <option value="https://www.example.com/language/fr/">French</option>
  <option value="https://www.example.com/language/de/">German</option>
  <option value="https://www.example.com/language/sp/">Spanish</option>
</select>

when i select any of these options it also open correctly, but it add double slash at the end of the link in the address bar like this

https://www.example.com/language/en//

i don't know the reason and how can i solve this problem i need to get rid of google redirect errors and at the same time get rid of the double slash at the end of links

please notice that i also don't want my links to open like this

https://www.example.com/language/en

Regards

Answer 1

as bro @Siguza mentioned me, the problem was in the menu java script code

it was like this

<script>
$(window).ready(function() {
    $(function(){
      /*/ bind change event to select*/
      $('#languages').on('change', function () {
          var url = $(this).val() + "/"; /*/ get selected value*/
          if (url) { /*/ require a URL*/
              window.location = url; /*/ redirect*/
          }
          return false;
      });
    });
});
</script>

and i changed it to this, everything is okay now

<script>
$(window).ready(function() {
    $(function(){
      /*/ bind change event to select*/
      $('#languages').on('change', function () {
          var url = $(this).val(); /*/ get selected value*/
          if (url) { /*/ require a URL*/
              window.location = url; /*/ redirect*/
          }
          return false;
      });
    });
});
</script>