Russian, Ukrainian and Belarussian are three languages. I learnt Russian, I understand Ukrianian pretty well, and Belarussian only in certain degree. On other hand I understand perfectly Croatian TV. Few months ago, there was request for Nova TV to title Serbian films, it was not good accepted, since TV auditorium understand it. There is certain difference in accent, you could determine who is from Varaždin, who is from Valjevo, there is certain difference in terminology (espetialy in scholary works), but unless there is some Čakavian or Kajkavian song Serbs will understan Croatian TV.