This uses the same engine as WEEKDAYS, a multilingual rebuild of a 1980s memory-aid program by John Higgins, applied here to the months of the year instead of the days of the week: point at a month and see it in context (this month / next month / last month), then test yourself if, but only if, you want to be — no marks for right answers, no scolding for wrong ones, just silence until you get it right.
Croatian keeps the same kind of grammar point WEEKDAYS makes with days — “last month” needs bio or bila depending on whether the month's name is grammatically masculine or feminine (all of them are, except February).