Add barley to boiling water, reduce heat to low, and simmer until the barley is tender, about 45 minutes, adding more water as necessary. Drain in a colander and let cool.

Combine tomatoes, cucumber, bell pepper, olives, feta, pine nuts, shallot, and mint in a large bowl. Add cooled barley and stir to combine.

Whisk together red wine vinegar and olive oil in a separate small bowl. Season with salt and pepper as desired. Drizzle over the salad and toss to coat. Cover and place in refrigerator until ready to serve.