/* When the user clicks on the button, 
      toggle between hiding and showing the dropdown content */
function myFunctionlang() {
  document.getElementById("myDropdown").classList.toggle("showlang");
}

// Close the dropdown if the user clicks outside of it
window.onclick = function(event) {
  if (!event.target.matches('.dropbtnlang')) {
    var dropdowns = document.getElementsByClassName("dropdownlang-content");
    var i;
    for (i = 0; i < dropdowns.length; i++) {
      var openDropdown = dropdowns[i];
      if (openDropdown.classList.contains('showlang')) {
        openDropdown.classList.remove('showlang');
      }
    }
  }
}

/*dropdown lang start*/

.dropbtnlang {
  background-color: #3498DB;
  color: white;
  padding: 16px;
  font-size: 16px;
  border: none;
  cursor: pointer;
}

.dropbtnlang:hover,
.dropbtnlang:focus {
  background-color: #2980B9;
}

.dropdownlang {
  position: relative;
  display: inline-block;
}

.dropdownlang-content {
  display: none;
  position: absolute;
  background-color: #f1f1f1;
  min-width: 160px;
  overflow: auto;
  box-shadow: 0px 8px 16px 0px rgba(0, 0, 0, 0.2);
  z-index: 1;
}

.dropdownlang-content a {
  color: black;
  padding: 12px 16px;
  text-decoration: none;
  display: block;
}

.dropdownlang a:hover {
  background-color: #ddd;
}

.showlang {
  display: block;
}


/*dropdown lang end*/

<link rel="stylesheet" href="https://cdnjs.cloudflare.com/ajax/libs/font-awesome/4.7.0/css/font-awesome.min.css" />

<a href="#"><i class="fa fa-fw fa-language" onclick="myFunctionlang()" class="dropbtnlang"></i></a>
<div id="myDropdown" class="dropdownlang-content">
  <a href="#about">Test</a>
</div>