Edit in JSFiddle

(function ($) {
    $('#add_single').on('click', function () {
        var text_to_add = $('#single_add_text').val();
        if ($.trim(text_to_add) == "") return;
        $('#languages1').append(
            "<option value='" + text_to_add + "'>" + text_to_add + "</option>");
    });
})(jQuery);

<br/>
<input type="text" id="single_add_text" class="form-control">
<button class="btn btn-primary glyphicon glyphicon-plus" id="add_single">Add</button>
<div class="code_example">
    <select name="languages" id="languages1">
        <option value="c">C</option>
        <option value="c++">C++</option>
        <option value="php">PHP</option>
        <option value="perl">PERL</option>
        <option value="ruby">RUBY</option>
        <option value="python">PYTHON</option>
        <option value="go">GO</option>
    </select>
</div>