that’s a really cute pattern. You can definitely add a lining to it. Just make a copy of the skirt in your lining fabric, I would baste the two together at the waistline before attaching a waistband. At the bottom, you can sew a couple tacking stitches at the hemline to attach them together at the bottom. At the vents, you can fold the lining in a little more on the edges, to make sure it doesn’t show on the right side and then use some slip stitches to hold the lining in place. Hope this helps.