JSFiddle - React, Tailwind, and code Playground

HTML

<link rel="stylesheet" href="https://maxcdn.bootstrapcdn.com/bootstrap/3.3.5/css/bootstrap.min.css">
<script src="https://maxcdn.bootstrapcdn.com/bootstrap/3.3.5/js/bootstrap.min.js"></script>
<nav class="navbar navbar-inverse">
  <div class="container-fluid">
    <!-- Brand and toggle get grouped for better mobile display -->
    <div class="navbar-header">
      <button type="button" class="navbar-toggle collapsed" data-toggle="collapse" data-target="#bs-example-navbar-collapse-1" aria-expanded="false">
        <span class="sr-only">Toggle navigation</span>
        <span class="icon-bar"></span>
        <span class="icon-bar"></span>
        <span class="icon-bar"></span>
      </button>
      <a class="navbar-brand" href="#">Brand</a>
    </div>

    <!-- Collect the nav links, forms, and other content for toggling -->
    <div class="collapse navbar-collapse" id="bs-example-navbar-collapse-1">
      <ul class="nav navbar-nav">
       <li><a href="#" class="btn btn-primary btn-xs highlight" onclick="changeToEn()"><span class="glyphicon glyphicon-flag"></span> EN</a></li>
<li><a href="#" class="btn btn-info btn-xs highlight" onclick="changeToDe()"><span class="glyphicon glyphicon-flag"></span> DE</a></li>
<li><a href="#" class="btn btn-success btn-xs highlight" onclick="changeToPl()"><span class="glyphicon glyphicon-flag"></span> PL</a></li>
          <li><a href="#" class="btn btn-primary btn-xs" onclick="changeToEn()"><span class="glyphicon glyphicon-flag"></span> EN</a></li>

      </ul>
    </div><!-- /.navbar-collapse -->
  </div><!-- /.container-fluid -->
</nav>

<li><a href="#" class="btn btn-primary btn-xs " onclick="changeToEn()"><span class="glyphicon glyphicon-flag"></span> EN</a></li>

CSS

.navbar-inverse .navbar-nav > li > a.highlight:hover,
.navbar-inverse .navbar-nav > li > a.highlight:focus {
    color: white;
    background-color: transparent;
    box-shadow: inset 0px 6px 0px white;
}
.navbar-inverse .navbar-nav > .active > a.highlight,
.navbar-inverse .navbar-nav > .active > a.highlight:hover,
.navbar-inverse .navbar-nav > .active > a.highlight:focus {
    color: white;
    background-color: transparent;
    box-shadow: inset 0px 6px 0px white;
}