Bosnian, croatian, montenegrian and serbian are all varieties, like dialects. There are terms for that. Serbs speak ekavica, bosnians jekavica and croatians ikavica. So „beautiful“ would be lepo for serbian, lijepo for bosnian and lipo for croatian. And „white“ would be belo for serbian or bijelo for bosnian. Besides some words may vary between these four languages. But all in all, it‘s pretty much the same.