A “safeguard against corruptions”

View from the Basilica of Saint Peter, Rome (photo credit: arounddeglobe.com)

“The use of the Latin language prevailing in a great part of the Church affords at once an imposing sign of unity and an effective safeguard against the corruptions of true doctrine.” ~ Pope Pius XII, Mediator Dei, Sec. 60 (Emphasis added)

So if the use of Latin goes from being a “great” part of the Church to a marginal and largely ceremonial part, what happens to the “imposing sign of unity” and “effective safeguard” against what Pope Pius XII calls “corruptions”?