It is difficult to imagine a work of literature of more importance to a national culture than Dante's The Divine Comedy. Not only did he write it in the Tuscan or Florentine Italian, this long poem helped make that dialect, or version of Italian, the standard one for Italy. However, the poem also pulled in words from other Italian dialects and other languages.
In the early 1300s when Dante wrote his masterwork, Latin was the international language widely used by educated people of Europe for their written texts. It was, therefore, unusual for Dante to write a major literary work in the vernacular, the native language of one's country, but Dante did so, along, it might be noted, with fellow medieval writers Petrarch and Boccaccio.
It's worth noting that 600 years later, Italian Primo Levi devotes a whole chapter of his book Survival in Auschwitz to regaining his sense of humanity for a short time while in the concentration camp simply by having the opportunity to recite a canto from The Divine Comedy to a fellow inmate.