Short answers, pulled from the story.
The Veronese Riddle dates to the 8th or early 9th century and stands as one of the earliest surviving texts that can be called vernacular. The Placiti Cassinesi legal formulae from Benevento date from 960 to 963 and represent the earliest surviving texts definitely classified as vernacular.
The Accademia della Crusca formed in Florence between 1582 and 1583 as the official legislative body of the Italian language. Pietro Bembo headed the purists faction who claimed language might be based only on great literary classics like Petrarch during the debate known as questione della lingua.
Current estimates indicate that between 68 and 85 million people speak Italian including approximately 64 million native speakers as of 2024. Italian serves as an official language in Italy San Marino Switzerland and Vatican City with official minority status in Croatia Slovenia Romania Bosnia and Herzegovina and six municipalities of Brazil.
A 1949 study by linguist Mario Pei concluded that Italian's stressed vowel phonology was second-closest to Classical Latin after Logudorese Sardinian. Pei assigned 12% change points to Italian compared to 44% for French and 8% for Sardinian while noting preservation of geminate consonants distinguishes Italian from Spanish.
Standard Italian derives from Tuscan especially its Florentine dialect as an Italo-Dalmatian language. Dante Alighieri wrote his epic poem Commedia in Florentine during the early 14th century and Alessandro Manzoni chose to write The Betrothed in Florentine dialect describing this choice as rinsing his Milanese in the waters of the Arno.