Every country's festive calendar has the same skeleton: one or two national celebrations with parades and fireworks, the major religious festivals of the dominant faith, a new year celebration (sometimes on a different calendar than January), and a harvest or seasonal festival rooted in the agricultural year. Layered on top are modern additions: a famous carnival, arts festival, or food event grown into an international draw.
The official tourism board calendar is the authoritative list with each year's dates, which matters because many festivals follow lunar or religious calendars and move annually.
For experiencing them well: the biggest national festival shows you the country at its proudest but also its most crowded and expensive, so book months ahead. Regional versions in smaller towns are often warmer and more genuine. And remember the flip side: during major holidays, shops close, transport sells out, and sightseeing pauses, so decide whether you are travelling for the festival or despite it.