Combine barley and plenty of cold water in a bowl and soak overnight. Drain.
Fill a stockpot with 6 cups of water. Add drained barley and bring to a boil. Reduce heat and simmer for 30 minutes.
Meanwhile, melt butter in a skillet over medium heat and cook onion until browned, about 5 minutes. Add mushrooms and keep cooking until they start to release their liquid, 5 to 10 minutes. Set aside.
After barley has been cooking for 30 minutes, add sauteed mushrooms, potatoes, carrot, bay leaves, dill, salt, and pepper. Cook for 10 more minutes. Add pickles and cook for 5 more minutes. If the water evaporates too much, you can add more.