So far, my searches have brought me either vague descriptions of the written Late Latin and spoken Vulgar Latin of the Italian peninsula toward the end of the Roman Empire and through the Western Roman Empire, and then later histories of the Italian language that start in the 12th century or some documents as early as the 10th century.
What is modern-day Italy's linguistic landscape in the 6th to 12th centuries, under influence of the invading Germanic tribes (the Ostrogoths, the Lombards, etc.)? Throughout what is modern Italy, what is spoken and written? Where does Vulgar Latin place itself in this period (geography and prominence), and how did this situation influence the evolution of Vulgar Latin dialects in these regions?
I am aware of various questions in this sub and the FAQ asking about when Latin died out, when the transition from a Latin to Italian identity occurred, etc., which are all too broadly asked and answered relative to my specific interest at the moment.
I understand this is a fairly pointed subject, so any suggested leads/key terms or ideas/literature would be quite appreciated. I am involved in academia but not in the humanities or linguistics, and my knowledge of the Late Antiquity and early Middle Ages is limited, so I'm somewhat unsure what I should be searching for (what kind of journal or book title keywords would be used), what books or journals would be most relevant, etc.
As the above implies, this is research out of personal interest—not related to coursework or academic research, if there are any such concerns with this question.
Thanks!
As a follow up question for context, what was the linguistic situation like in Italy on the eve of unification in the 1860s? And what about today? Do different dielects still exist?
Part of the difficulty in tracing the change in language is how influential the classical writers were. During the 1st Century BC, the common people no longer spoke Classical Latin. Probably the clearest example was Publius Clodius Pulcher. He is from the Claudius family, but vulgar Latin had a vowel shift that turned au into o (a lot of Italian words do this to Latin, with the -us at the end becoming an -o). To signify he was a member of the Plebian class, he changed the spelling of his name to match. However, historians continued to write in classical Latin. Likewise, other important records did the same.
The oldest known writings in Italian are the Placiti Cassinesi and the Veronese Riddle. One is 8th Century, the other is 10th Century However, just because these are the first recorded instances doesn't mean everyone suddenly stopped speaking Latin and started speaking Italian. Instead, writings took time to catch up to the popular language. In addition, as you can see from those links, some debate whether these sources are even Italian instead of Latin. That should make it clear that there really isn't a clear dividing line between the two. Instead, there's a gradual transition.