It can be normal. Barking is very self rewarding and can be a hard behaviour to crack. Obviously it is causing some issues for you, so whether it is normal or not is irrelevant. It is unaccpetable behaviour for you, so you need to train it.
How you would train for it would depend upon why the dog is barking? It could be excitement, fear, a bit of both, fustration because he wants to play but can't. If you can't tell or you're not sure why he is barking you'd be better off contacting an APBC behaviourist or APDT trainer to help you.
BAT (behaviour aversion therapy) should help with most issues if it is only one specific thing he barks at e.g dogs in your case, so if you can't afford a trainer, then reading up on BAT would help.
My pup barks when is off lead to get other dogs to chase him. I don't find this acceptable because he does it incessantly and it often scares the other dogs who then end up snapping at him. His fault, not theirs. I am working on this by stepping between him and the other dog and ending his game until he is quiet, when I release him again. He has improved dramatically since I started this, but generalisation is an issue. He now knows he cannot bark at his collie friend, or my Dad's whippet, but doesn't generalise that to his JRT friend because we don't see him often enough to have trained it well enough yet. But it can be done, it just takes time and patience, so don't give up if you don't get results straight away or if the results seem hit and miss.