BootStrap 4 multilingual site menu is a simple example of how to do a multilingual selector menu in BootStrap 4 .
because of the way BootStrap works, it requires JavaScript on and JQuery loaded
useful for i18n (internationalization) and i10n (localization)
navbar.htmk
<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="utf-8">
<meta http-equiv="X-UA-Compatible" content="IE=edge">
<meta name="viewport" content="width=device-width, initial-scale=1, shrink-to-fit=no">
<meta name="description" content="">
<meta name="author" content="">
<title>Multilingual Menu in Navbar Template for Bootstrap</title>
<!-- Bootstrap core CSS -->
<link href="https://maxcdn.bootstrapcdn.com/bootstrap/4.0.0/css/bootstrap.min.css" rel="stylesheet">
<link href="https://cdnjs.cloudflare.com/ajax/libs/flag-icon-css/3.1.0/css/flag-icon.min.css" rel="stylesheet">
<!-- Custom styles for this template -->
<link href="navbar.css" rel="stylesheet">
</head>
<body>
<div class="container">
<nav class="navbar navbar-expand-lg navbar-light bg-light rounded">
<a class="navbar-brand" href="#">Navbar</a>
<button class="navbar-toggler" type="button" data-toggle="collapse" data-target="#navbarsExample09" aria-controls="navbarsExample09" aria-expanded="false" aria-label="Toggle navigation">
<span class="navbar-toggler-icon"></span>
</button>
<div class="collapse navbar-collapse" id="navbarsExample09">
<ul class="navbar-nav mr-auto">
<li class="nav-item active">
<a class="nav-link" href="#">Home <span class="sr-only">(current)</span></a>
</li>
<li class="nav-item">
<a class="nav-link" href="#">Link</a>
</li>
<li class="nav-item">
<a class="nav-link disabled" href="#">Disabled</a>
</li>
<li class="nav-item dropdown">
<a class="nav-link dropdown-toggle" href="http://example.com" id="dropdown09" data-toggle="dropdown" aria-haspopup="true" aria-expanded="false"><span class="flag-icon flag-icon-us"> </span> English</a>
<div class="dropdown-menu" aria-labelledby="dropdown09">
<a class="dropdown-item" href="#fr"><span class="flag-icon flag-icon-fr"> </span> French</a>
<a class="dropdown-item" href="#it"><span class="flag-icon flag-icon-it"> </span> Italian</a>
<a class="dropdown-item" href="#ru"><span class="flag-icon flag-icon-ru"> </span> Russian</a>
</div>
</li>
</ul>
<form class="form-inline my-2 my-md-0">
<input class="form-control" type="text" placeholder="Search" aria-label="Search">
</form>
</div>
</nav>
</div>
<!-- Bootstrap core JavaScript
================================================== -->
<!-- Placed at the end of the document so the pages load faster -->
<script src="https://code.jquery.com/jquery-3.1.1.slim.min.js" crossorigin="anonymous"></script>
<script src="https://maxcdn.bootstrapcdn.com/bootstrap/4.0.0/js/bootstrap.min.js"></script>
</body>
</html>navbar.css is actually rather superfluous
body {
/*padding-top: 20px;*/
padding-bottom: 20px;
}
.navbar {
margin-bottom: 20px;
}