Do words for months, seasons, weekdays and holidays have any meaning?
Mostly. For literal translations of months go to Months. Nedjelja (Sunday) is derived from ne djelati, slavic word meaning not to work, ponedjeljak (Monday) could roughly mean “after sunday”, četvrtak (Thursday) is derived from četvrti which means the fourth and petak (Friday) is derived from peti meaning fifth. As for the holidays, Božić (Christmas) could be roughly translated as little god, Uskrs (Easter) is derived from uskrsnuti, meaning “to resurrect” and Nova godina does indeed mean New year.