JSFiddle - React, Tailwind, and code Playground

HTML

<script src="http://code.jquery.com/jquery-1.11.3.min.js"></script>
<select id="first-choice">
   <option value="English">English</option>
   <option value="Spanish">Spanish</option>
</select>

<select id="second-choice">
   <option value="Spanish">Spanish</option>
   <option value="English">English</option>
</select>

JavaScript

$("#first-choice").change(function() {
    var selected = $(this).val()
    if(selected== "English"){
        $("#second-choice option[value='Spanish']").attr("selected","selected");
    }
    else if(selected == "Spanish"){
		$("#second-choice option[value='English']").attr("selected","selected");
    }
});

$("#second-choice").change(function() {
    var selected = $(this).val()
    if(selected== "English"){
        $("#first-choice option[value='Spanish']").attr("selected","selected");
    }
    else if(selected == "Spanish"){
		$("#first-choice option[value='English']").attr("selected","selected");
    }
});