About the Mass in the Vernacular
March 7, 1965, was the first “Mass in Italian” to be ever celebrated.
The original Mass was celebrated by Paul VI on March 7, 1965, which happened to be that year’s First Sunday of Lent. The repeatedly vandalized plaque now marking the event goes so far as to say that it was this event that inaugurated the liturgical reform decreed by Vatican II.
(The text of the plaque says, “On March 7, 1965, His Holiness Paul VI, inaugurating the liturgical reform decreed by the Second Ecumenical Council of the Vatican, deigned to celebrate in this temple the first mass in Italian language, amidst the emotion and joy of an entire people, forever faithful and grateful.”)
The rite used by Paul VI was the so-called “1965 Missal”, essentially the 1962 Missal but with the modernization and simplifications laid out in 1964 by Inter oecumenici, which came into force on the same day as the Pope’s Italian Mass.
The actual Mass, celebrated by Paul VI himself, served as the inauguration of the “1965 Missal”. It would not have been entirely in Italian because Inter oecumenici mandated that the Orations, Preface, and the silent priestly prayers including the Roman Canon (which continued to be said inaudibly) were to remain in Latin.
It also ordered that “Missals to be used in the liturgy, would contain, besides the vernacular version, the Latin text”. Messa in Latino recently published a few pages from a 1965 Italian-Latin Missal showing the bilingual Ordo Missae.
(In the USA, vernacularization was already being implemented as early as 1964. The US Bishops’ November 1964 document includes rules for the use of Latin and the vernacular.)