Uh, obviously. But they came before 1800, not in 900.
Unless one subscribes to the Paleolithic Continuity Theory.
Right. I alluded to that earlier - specifically to the fact that no one subscribes to it. 
Fine. Whatever. Like I said,
I wasn’t accusing you of anything. Polycarp had asked John Mace for more information on the topic, and your post was the most recent post about it.
Venetian is a Romance language. Venetic seems to have been a non-Italic Indo-European language, but not a Celtic one either.
There are at least three different tribes that are called the Veneti. One, the Adriatic Veneti, spoke Venetic. Another, the Brittany Veneti were Celts, but they lived in Brittany, not in Venice. The third is the Baltic Veneti or “Venedes,” who lived in what is now Poland.
That may be what the author was talking about. I wish I could remember where I read it! It’s entirely possible that I read it not in an essay or article, but in an isolated context where it was simply presented as a point of interest without further explanation.
(bolding mine) This was very likely the context in which the writer was making his statement.
Well, thanks for all the information, everyone! This has been one of those things that’s been stored away in my brain for a very long time, and I finally got around to trying to clarify it. Consider this a case of Ignorance Fought 
Likely so. At a certain point, as the various branches of Vulgar Latin began spinning off, the Church stepped in and said, “OK, to regularize things, THIS is what we’ll use as our Standard Official Language” and picked one particular version. From what I understand, it was not Classical Latin any more, but more like a “business” Latin, combining standard grammar with the pronunciations of the Roman Vulgar dialect; thus it shares many pronunciations with Italian.
Heck, I learned things here too! Very succesful thread, I must say!
One thing I kept meaning to mention was something the OP alluded to. The Church does claim that it uses Latin specifically because it’s a dead language - and thus words don’t change over the time. Something akin to Humpty Dumpty’s line from Alice in Wonderland: “‘When I use a word,’ Humpty Dumpty said, in a rather scornful tone, ‘it means just what I choose it to mean, neither more nor less.’”
Church Latin pronunciation is explicitly based upon Italian. For instance, in Classical Latin, the letter C always represented the ‘hard’ sound, /k/. Thus, Caesar was imported into German as Kaiser, and so forth. Church Latin uses the Italian pronunciation - /k/ before A, O, U, and the sound represented in English as “ch” before E, I. Other pronunciations were set the same way - by applying Standard Italian pronunciation to Latin. This is not akin to the Latin of any place or time - it’s simply the usage in Italian, which - due to location - is a common everyday language for Church officials. It’s entirely arbitrary; it wasn’t done out of any desire to restore “proper” Latin pronunciation but just as a standard that could be used across the world in the Church. Prior to that time, Latin was spoken in churches in much the same way we use other Latin phrases - pronounced according to the pronunciations of the speakers’ respective native languages.
Excalibre, sorry to nitpick again, but I’m pretty sure Church Latin’s pronunciation is a relic of when it was ‘fossilized’ into Church Latin - that is, the early Medieval period, which really has little to do with Italian. By the Medieval period, the guesses we have about classical pronunciation (c=k, v=w) cease to be used.
Which part of the Medieval period? Is there any difference between Latin and Italian in 477 AD? Perhaps the same influence that changed the pronunciation in Italian also changed the pronunciation in Ecclesiastical Latin.
Another thing I’ve been curious about: how long was Latin used as an international language, used when say Bavarians and Sicilians needed to communicate?
Italian didn’t yet exist in 477 CE, by conventional definitions. The language spoken in Italy was still Latin then, although a late form. It’s absolutely the case that the changes are related - I don’t know the timeline (as past ~500 CE, I’m useless) but at a certain point well past Classical Latin, when the phonetic changes were already in place: a) the Church adopted a formal form of Latin in some sort of official capacity and b) everyone else went on talking ‘Vulgar Latin’, and the language changed (as they do) and it became Italian.
As to your second question, I’m also not sure. But I am currently translating a medical text written in Latin in 1629, and I’m pretty sure books in classics and biology continued to be written in Latin well into the 18th century. That still doesn’t answer your question about spoken Latin, but it gives a hint, I suppose!
Again I’m not sure what you’re even trying to claim here. Church Latin’s pronunciation was explicitly set out by the Church. I’m not sure what you even imagine the alternative could have been. The Middle Ages are normally dated from the collapse of the Roman Empire; the language spoken in the wreckage of Roman Europe was called either Late Vulgar Latin or Romance. If you’re thinking that Church Latin is essentially this language, you’re simply incorrect. Church Latin doesn’t show any of the sound changes characteristic of Late Vulgar Latin - lenition of intervocalic consonants, loss of H, loss of syllables just before or after the tonic, etc. etc. Not only that, but the “soft” C sound found in Church Latin - English “ch” - most likely wasn’t present in any of the Romance dialects at that time - it developed in Italian (and similar sounds developed in the other Romance languages) ofter centuries; at that time, the sound would have been a palatalized velar stop, not a palatal africate.
Church Latin is not really a natural language. It’s an artificial dialect of Classical Latin; it doesn’t show the typical changes of Late Vulgar Latin; the anomalous pronunciations typical to it are not the result of a natural evolutionary process but just what happens when you graft foreign pronunciations onto a language.
I’m going to start with responding to the above post, although Excalibre has addressed issues related to this already in another post previous to this one (mine).
What I believe to be the case is that Late Latin moved in the direction of the “Romance” consonantal and vowel sounds – the sounds common to Spanish, Portuguese, and Italian, among others (as opposed to those unique to one particular language). V took on a /v/ sound as opposed to a /w/ sound, E took on the sound in hey as opposed to that in heh, and so on. I imagine there are some efforts to reconstruct the phonology at various dates, but they would range from inferential to speculative.
What is certain is that Church Latin finally settled on a sound system very closely akin to learned Florentine Italian, the “prestige” dialect, and has been using that for several hundred years. (I’d guess Renaissance times as a likely target date for when that “several hundred years” begins.) The issue of what if anything was standard Church Latin prior to that time must be speculative.
It was quite a bit later than that – the Italian pronunciation didn’t become ascendant everywhere until the Ultramontanes finally won in the 19th century.
Before that, there were multiple Church Latin pronunciations. All the regions of Catholic Europe – the Slavic areas, the Germanic, French, Spanish, Italian, and English – had their own systems of pronouncing Latin, based on the common languages spoken there. The French even went so far as to nasalize vowels, and drop final consonants (except when liaison was called for). Certainly Rome would have spoken Latin with an Italian accent, but most other places didn’t.