Cook the barley: Rinse the pearl barley thoroughly. In a medium saucepan, cook it in salted water (about 3 parts water to 1 part barley) for 25–30 minutes until tender but not mushy. Drain and let cool.
Prepare the filling: In a large bowl, mix the ground pork, cooked barley, chopped onion, minced garlic, salt, allspice, black pepper, and herbs (if using). Add a little broth or water if the mixture feels too dry.
Stuff the casings: Slide one end of the soaked casing onto a sausage stuffer or funnel. Fill carefully with the pork-barley mixture, making sure not to overstuff. Twist into 10–12 cm links and tie off with string if needed.
Simmer the sausages: Bring a large pot of water to a gentle simmer (do not boil). Add the sausages and cook for 20–25 minutes until firm. Remove from water and let rest.
Finish by pan-frying or roasting: For the best texture and flavor, pan-fry the sausages in a little butter or oil until golden and crispy on the outside. Alternatively, roast them in the oven at 200°C (390°F) for 10–15 minutes.