Italian here, and have to say that, sadly, @iphisesque in the second reblog is incorrect, as the reality is even crazier: standard Italian is essentially 1850s Florentine dialect that was spun off for literary reasons and imposed over 30 or 31 different languages for political reasons, with the Italian state desperatedly pretending that the majority of said languages are dialects (something that is true only for Tuscan and Romanesco, as Tuscan is where standard Italian comes from and became a dialect when standard Italian became dominant and Romanesco is a dialect of Tuscan, even if Rome is NOT in Tuscany. There’s a reason for this) and linguists not being fully sure if a certain group of dialects counts as their own language or belongs to another.
Here’s more or less how it happened: with the Roman conquest, Latin gradually replaced all other languages, but with the Lombard invasion in 568 political unity was broken and the historical Italian region started receiving contributions from further invasions and migrations, and the various regions started speaking their own languages, mostly relatively similar (hence why the Italian government can pretend they are dialects), but in the border areas and in a few enclaves they may have heavier contributions from outside or be outright non-Italian languages.
In the 1300s the sheer literary power of Florentine poets such as Dante, Petrarca, and Boccaccio imposed Florentine dialect of that time as “Italian”, but it was only spoken as a common language by elites when they needed to speak with each other while everyone primarily spoke their own language.
Then after Napoleon’s First Campaign of Italy brought the ideals of the French Revolution people started talking of Italian unification, especially after the creation of the “Sister Republics” and a full-on Republic of Italy (with Napoleon as president) and later Kingdom (and guess who was the king?), and while the Congress of Vienna rejected the idea because Italy was “a mere geographical expression” (and in all fairness that’s what it had been for a long time), patriots started working toward an Italian state that covered the entire historical Italy (plus Savoy because it was part of an Italian state. That gave it away to France alongside Nice as payment for help in the Second War of Italian Independence)… And of course the problem of the language came up, as there were 30 or 31 different languages spoken, and while some were reduced in speakers others were big, and the “Italian” used as a common literary language had remained stuck to the 1300s.
The language debate was fierce, with the main candidates being MODERN Florentine (because its ancestor was already the common literary language), Romanesco (and that would have been fun, considering the sheer amount of vulgarities), the Neapolitan dialect of Southern Italian (as the Kingdom of Two Sicilies, with capital in Naples, was the biggest and richest state in the Peninsula), and Lombard (as Lombard had a literary might that matched Tuscan, and was the biggest part of the Gallo-Italic language group that was spoken by the most people and covered the most areas)… And then, straight out of Milan, Alessandro Manzoni wrote the novel Fermo e Lucia in Lombard, didn’t like it and rewrote it twice as I Promess Sposi (The Betrothed) using the Florentine dialect, and the sheer popularity of the final 1848 edition abruptly settled the debate in favor of Florentine, with the Kingdom of Sardinia, that was leading the unification effort, promptly switching from “Italian” to the new standard of Italian as its official language and championing it as it expanded and became the Kingdom of Italy. And then starting to suppress the local languages, with amusing results such as the Gulf of the Sea Balls in Sardinia being renamed as the Gulf of Orange Trees because aranzos (Sardinian for “sea balls”) sounds similar to aranci (Italian for “orange trees”) and the official who read Cala'e sos aranzos on an old map and Italianized the name on the new one didn’t speak Sardinian (why do I hear a kangaroo jumping?), and the sheer amount of the slang words for “vagina” around the Boot. As for the official proper Italian name? It’s vagina. Because English took it from French, and both French and Italian got it straight from Latin.
As for the languages of Italy, they are:
Southern Italian dialects: spoken in southern Lazio and southern Marche and almost everywhere on the Peninsula south of it.
Median Italian dialects: spoken in Lazio except Rome and the south, Marche except the south, Umbria, and the extreme west of Abruzzo. May or may not be actually Southern Italian - I’m not a linguist and not from this area and I like my nose whole, so I’m not expressing any opinion.
Extreme Southern Italian dialects: spoken in Salento (the “heel” of the Boot), central and southern Calabria (the “toe”), and Sicily. Also known as Sicilian because that’s where most speakers are.
Venetian: Spoken in Veneto, Friuli-Venezia Giulia, and areas of Trentino-Alto Adige.
Lombard: Gallo-Italic language spoken in Lombardy, western Trentino, eastern Piedmont, and a couple Cantons in Switzerland. The language of my hometown.
Piedmontese: Gallo-Italic language spoken in Piedmont, southern Aosta Valley, and northern Liguria. Has heavy French influences.
Ligurian: Gallo-Italic language spoken in Liguria, southern Piedmont, areas of Lombardy and Emilia-Romagna, and Sulcis (in southern Sardinia).
Emilian: Gallo-Italic language spoken in Emilia (western Emilia-Romagna), areas of Lombardy, Tuscany, and Liguria, southern Veneto.
Romagnolo: Gallo-Italic language spoken in Romagna and Romagna Toscana (an area that was linguistically and culturally part of Romagna but politically controlled by Florence from the end of the 14th century to 1923, when Mussolini, a Romaboo even by Italian standards, reassigned most of the area to Romagna so that the Tiber river would be born in his native Forlì province).
Gallo-Picene: Gallo-Italic language spoken in the Piceno area of the Marche (blame the Lombards, they controlled this area until Charlemagne).
Gallo-Italic of Basilicata: Gallo-Italic language spoken in a few comuni in Basilicata (the “sole” of the boot). Nobody’s sure how it happened, as the Lombards did NOT invade this area and linguists hadn’t even noticed until 1931.
Gallo-Italic of Sicily/Sicilian-Lombard Dialects: Gallo-Italic language spoken in a few comuni in Sicily. The linguistic remnant of the Normans expelling a large chunk of Muslim population of Sicily and replacing it with Piedmontese immigrants in a time where everything north of the Po river was called Lombardy.
Sardinian: spoken in Sardinian, and the closest thing we have to actual Latin language in common use. Also the reason why Sardinian students of Latin pronounce it the Roman way and not the Church way like the rest of Italy.
Gallurese: spoken in Gallura, an area of Sardinia.
Sassarese: spoken in the Metropolitan City of Sassari, in Sardinia.
Friulan: Reto-Romance language spoken in Friuli-Venezia Giulia and areas of Veneto.
Ladin: Reto-Romance language spoken in Veneto and Trentino.
Tuscan: spoken in Tuscany and Rome. The one actual dialect.
German (including Sudtirolese dialect), Bavarian, Cimbrian, and Mocheno: Germanic languages spoken in Alto Adige (historically part of the County of Tirol), Friuli-Venezia Giulia, and Veneto, that is the areas historically controlled or closer to the lands of the House of Habsburg. Also, for some reason, in the Aosta Valley.
Arbërisht: a derivative of Tosk Albanian, it’s spoken in the areas of Southern Italy and Sicily where Albanian refugees escaping from the Ottoman expansion settled in the 15th century.
French: spoken in the Aosta Valley (historically part of the domains of the House of Savoy, itself a more-or-less French noble house that happened to be in the Holy Roman Empire, hence the historical French attempts to conquer both Savoy and Aosta).
French-Provenzal: spoken in the Aosta Valley and eastern Piedmont. Also in Puglia (in Southern Italy. Salento is part of the Puglia region). Can’t blame the Normans, their French was from the north and Provence is in the south.
Occitan: yet another French language, again spoken in the Aosta Valley, areas of Piedmont, and Puglia. Can’t blame the Normans for this either, it’s another southern France language.
Slovenian: spoken in Friuli-Venezia Giulia (historically claimed by Slovenia just as Venice claimed Slovenia. I am NOT going into this more beyond saying that Jugoslavia got about two thirds of Friuli-Venezia Giulia for Slovenia and Croatia after World War II, I don’t know nearly enough).
Alguerese: a CATALAN dialect spoken in the city of Alguero, in Sardinia. The linguistic remnant of Aragonese control over Sardinia (Catalonia being part of the historical Crown of Aragona).
Italiot Greek: spoken in Bovesia (the tip of the “toe” of the Boot) and Salento. Either the last stubborn linguistic remnant of the Ancient Greek colonization of Italy (the “Greater Greece”, as we call it. Conveniently forgetting that this “Greater Greece” included areas of southern France and western Anatolia), or the result of immigration from Greece in the Middle Ages as they were part of the areas controlled the longest by the Roman Empire after the switch to Greek and the arbitrary reclassification to “Byzantine”.
Walser: Alemannic language spoken in Piedmont and Aosta Valley, well away from other Walser speakers in Switzerland and Austria. No idea how it happened.
Molise Slavic: spoken in Molise, in Central Italy. The linguistic remnant of Croatian refugees that escaped the 15th century and settled in Italy, in a much larger area than the current one. Being murdered by the Italian government.
As for why Rome speaks a dialect of Tuscan… Blame the Landsknechte, their stingy master Holy Roman Emperor Charles V, and whoever told him to station Protestant soldiers in Rome: in 1527, after months of not being paid, the Landsknechte stationed in Rome decided to sack the City and ran out much of the population, and since the Pope at the time Clement VII was from Florence (he was in fact a member of the Medici family. THOSE Medici, the same as Lorenzo “The Magnificent” De Medici) that’s where the immigrants to repopulate the City came from, bringing their 16th century Florentine… And being influenced by the remaining Romans mostly in the LEGENDARY amount of swearwords and vulgarity that modern Romanesco still has and that may have a woman call her own child a “son of a whore” simply to add emphasis to whatever else she was saying, has a friend greet another with “How are you? May you get killed!”, and one express strong disapproval with “Go get yourself killed” (you may want to hear the actual insults. They are incredibly creative).