Take him to pet food stores, first during what should be quiet times. Do this 3x at least per week. He may or may not run into another dog, if he starts to bark at them - correct him. Then try to move to create more distance between your dog and the other dog, and distract him with a toy or treats.
Do you have friends with well behaved dogs? Take him for a visit. Keep him on lead, and plan the visit with your friends. They need to know his challenges, so that they can help you socialize him. Maybe their dogs are kept in crates until everyone settles in.
Puppy classes are also very good to do with him. The trainer will help you with the barking corrections, and heck you are all in the same situation needing to learn how to behave with each other
Work on the no bark command at home. Also use either your TV or Computer find dog programs that may have dogs barking in the background see how he re-acts.
Good luck