This code snippet demonstrates how to achieve this functionality using pure JavaScript:
document.getElementById("mySelect").selectedIndex = "0"
<select class="selectpicker" id="mySelect">
<option>English </option>
<option>Español </option>
</select>
If you want to accomplish the same task but in AngularJS, you can use the following controller setup:
app.controller("BodyController",function($scope){
/****************AngularJS code goes here*/
});