St. Isidore of Seville (Doctor of the [Roman Catholic] Church), ca.
AD 560-636, can be cited as the world's last native-speaker of Latin
(together with his family, to include St. Leander). Isidore may also
be cited as the first native-speaker of [proto]-Spanish. Read all
about him here:
http://www.newadvent.org/cathen/08186a.htm
I think I and all the other educated native-speakers of Modern English
are experiencing what Isidore experienced, tho' far more extremely
(Isidore did not, statistically, have as many educated native-speakers
competing with him).
The evidence is mainly in the collapse of the subjective-objective
distinctions in the pronouns. It it I/me. Us/we Amerians. Who/m do you
trust for the correct third millennium usage of English grammar. And
with pronouns in general: which and that are also under assault (they
tend to get dropped altogether).
The collapse of Latin was mostly phonological, which lead to some new
grammar. Eventually, one could not write vernacular dialects *as*
Latin, and had to lapse into the vernacular. Right now, Shakespeare
and the King James Bible are officially Modern English, but everyone
agrees they are 'archaic' or 'classical' English, literary
representives of a language that is not current, but which is
ancestral to the current language. Modern English, is, after all, a
rather old language, imputed a grammatical life that is chasing
post-archaic -- pre-Byzantine Greek for sheer longevity.
I sorta think of myself as using a language that AD 370 Greeks used:
One read Homer as one currently does Shakespeare and Spenser,
Sophocles as Dr. Johnson and St. Mark as something like Dickens. The
Eastern Nicaean Fathers would be the speakers of the current language.