Я немного изменил HTML. Но, самая большая часть заключается в том, что позиционированием языковой кнопки манипулируют так, что загрузчик по умолчанию может работать без перекодирования css. Меню гамбургера находится справа, поэтому я переместил его влево от меню, используя position: absolute;
и right: 100px;
<link rel="stylesheet" href="https://use.fontawesome.com/releases/v5.6.3/css/all.css" integrity="sha384-UHRtZLI+pbxtHCWp1t77Bi1L4ZtiqrqD80Kn4Z8NTSRyMA2Fd33n5dQ8lWUE00s/"
crossorigin="anonymous">
<link rel="stylesheet" href="https://stackpath.bootstrapcdn.com/bootstrap/4.2.1/css/bootstrap.min.css" integrity="sha384-GJzZqFGwb1QTTN6wy59ffF1BuGJpLSa9DkKMp0DgiMDm4iYMj70gZWKYbI706tWS"
crossorigin="anonymous">
<link rel="stylesheet" href="https://cdnjs.cloudflare.com/ajax/libs/flag-icon-css/3.2.1/css/flag-icon.min.css">
<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>
<style type="text/css">
.phone-link {
border-radius: 25px;
background-color: lightblue;
color: #ffffff;
padding: 15px 25px;
}
.navbar-nav {
margin-right: 40px;
}
.navbar-nav .nav-item {
padding: 25px;
}
@media (max-width: 999px) {
.phone-link {
display: none;
}
}
.dropdown.language {
position: absolute;
right: 200px;
width: auto;
top: 35px;
}
@media (max-width: 991px) {
.dropdown.language {
right: 100px;
position: absolute; top: 10px;
}
}
</style>
<nav class="navbar navbar-expand-lg navbar-light bg-light">
<a class="navbar-brand" href="#">
<img src="https://getbootstrap.com/docs/4.2/assets/brand/bootstrap-solid.svg" width="30" height="30" alt="">
</a>
<button class="navbar-toggler" type="button" data-toggle="collapse" data-target="#navbarNavDropdown" aria-controls="navbarNavDropdown" aria-expanded="false" aria-label="Toggle navigation">
<span class="navbar-toggler-icon"></span>
</button>
<div class="collapse navbar-collapse" id="navbarNavDropdown">
<ul class="navbar-nav">
<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="#">Features</a>
</li>
<li class="nav-item">
<a class="nav-link" href="#">Pricing</a>
</li>
<li class="nav-item dropdown">
<a class="nav-link dropdown-toggle" href="#" id="navbarDropdownMenuLink" role="button" data-toggle="dropdown" aria-haspopup="true" aria-expanded="false">
Dropdown link
</a>
<div class="dropdown-menu" aria-labelledby="navbarDropdownMenuLink">
<a class="dropdown-item" href="#">Action</a>
<a class="dropdown-item" href="#">Another action</a>
<a class="dropdown-item" href="#">Something else here</a>
</div>
</li>
</ul>
</div>
<div class='phone-link'>
<a href="tel:12-12-12-12"><i class="fas fa-phone fa-rotate-90"></i>12 12 12 12</a>
</div>
<div class="dropdown language">
<button class="btn btn-secondary dropdown-toggle" type="button" id="dropdownMenuButton" data-toggle="dropdown" aria-haspopup="true" aria-expanded="false">
<span class="flag-icon flag-icon-us"></span> English
</button>
<div class="dropdown-menu dropdown-menu-right text-right language">
<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>
</div>
</nav>