Alehana,
файл data.json добавьте самостоятельно.
<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<title>Document</title>
</head>
<body style="padding: 1em;">
<script src="https://ajax.googleapis.com/ajax/libs/jquery/1.12.4/jquery.min.js"></script>
<link rel="stylesheet" href="https://dbrekalo.github.io/fastselect/dist/fastselect.min.css">
<script src="https://dbrekalo.github.io/fastselect/dist/fastselect.standalone.js"></script>
<script>
$(function() {
$('.demo, .multipleSelect').fastselect();
});
</script>
</body>
<input
type="text"
multiple
class="demo"
value="Algeria,Angola"
data-initial-value='[{"text": "Algeria", "value" : "Algeria"}, {"text": "Angola", "value" : "Angola"}]'
data-url="data.json"
data-load-once="true"
name="language">
<input type="text" multiple class="demo" data-url="data.json" name="language">
<select class="multipleSelect" multiple name="language">
<option value="Afghanistan">Afghanistan</option>
<option value="Albania">Albania</option>
<option value="Algeria">Algeria</option>
<option value="Andorra">Andorra</option>
<option value="Angola">Angola</option>
</select>
</html>