This is a complicated question, national identity is a complicated and fuzzy thing and I am not sure I or anyone can give you a perfectly accurate answer, but I will try my best. I think there are two possible answers:

If the question is when did Italians start feeling that they were part of common unitary cultural entity, in other words a nation? The answer is: Probably from the Renaissance and way before unification was ever even a political possibility. Nation and State are two different things, for a common national identity to develop one doesn’t necessarily need a common state.

This quote from Francesco Algarotti explains it really well in his “Saggio sulla lingua francese”: “ Da non picciola maraviglia dovrà esser presa buona parte degli uomini di lettere al vedere come la lingua francese, la quale si parla da tanti secoli in un paese ridotto sotto a un principe solo, sia stata sempre incerta e mutabile; e solamente da picciolo tempo in qua ricevuto abbia un qualche regolamento; dove la lingua italiana, la quale si parla in un paese diviso in tanti stati come è il nostro, è venuta su quasi dalla prima sua infanzia bella e formata, ha ricevuto regole di buon’ora e da quel tempo sino a’ giorni nostri si è mantenuta sempre la istessa.”

Here is the translation: “No little surprise is expressed by learned men when they discover how the French language, that as been spoken for a long time in a country under one king, has always been flexible and in continuous change, while the Italian language, that is spoken in a country divided in many states like ours, came up in it’s infancy already formed, it received rules at that time and from that time forward it maintained itself the same.” This is the view of a Venetian during the 1750, almost a 100 years before the unification. When Algarotti speaks about Italy he clearly identifies it as one single cultural entity (a nation) divided in many states.

More interesting is what Algarotti sense of identity was, which we can identify from the following quote in “Saggio sulla necessita di scrivere nella propria lingua” : “Not a few French geniuses attempted in the past century to compose in our language, when Italian things were beyond mountains in such reputation, that those who did not know our manners were not kept kind as were those who were not very familiar with our authors. At that time, some Frenchmen were made to pick up some composition that had a lot of semblance and Italian genius by force of imitation. Such are among several other examples that could be adduced, the Lives of Lionardo da Vinci and Leonbatista Alberti written by Raffaello Dufresne…”. From this quote is obvious that Algarotti identifies himself as an Italian. Even more interesting is however how other people defined him. During the various letters exchange he had with foreign interlocutor most of them referred to him as Italian. During his fall-out with Frederick the great of Prussia, Frederick seemingly attempted to lure him back in to his court through flattery and wrote in one of his letters “je m'étonne de cet exces de modestie chez un italien qui s’est fait imprimer, e qui est affiche comme bel esprit, en verse et en prose par tutt l'europe” “I am astonished at this excess of modesty in an Italian who made a name for himself, and who is displayed as a fine spirit, in verse and in prose by all Europe” (sorry for the poor translation, French is not my first language nor my second) Another famous example is in the correspondence of Frederick and Voltaire where Frederick complains of Algarotti’s beliefs that Italians are more prone to feelings that the “inhabitants of the north”.

This phenomenon is in no way unique to Algarotti most Italians abroad would define themselves as Italians. This is the case also for Giacomo Casanova (Venetian as well and born in 1725). In his memoirs often he refers to himself as Italian and to other Italians as Italians. For example, one time he meets another Italian, a beautiful girl from Parma. During that encounter he refers to himself as a fellow countryman, or in the French original as “compatriote”. From his memoirs : “ In the morning I was told that there were two young Italians, brother and sister, who did not appear very wealthy, in the next room to mine. Italians, young, poor and newly arrived, my curiosity was excited. I went to the door of their room, I knocked, and a young man came to open it in his shirt.

“I beg you to excuse me, sir,” he said to me, “if I receive you in such a state.”

“I have to ask your pardon myself. I only come to offer you my services, as a countryman and as a neighbour.”

While, always in his Memoirs, during an argument with a Frenchman this exchange comes up:

“During the last month,” he added, “the Place de Greve has seen the hanging of seven men, among whom there were five Italians. An extraordinary circumstance.” (says the Frenchman)

“Nothing extraordinary in that,” I answered; “honest men generally contrive to be hung far away from their native country; and as a proof of it, sixty Frenchmen have been hung in the course of last year between Naples, Rome, and Venice. Five times twelve are sixty; so you see that it is only a fair exchange.” (says Casanova)

As you can see not only most Italians already defined themselves as such pre-unification, but most people in the rest of Europe did to. So, a first answer could be that because “state” and “nation” are two separate things one does not need a unitary state to feel part of a common nation.

However, if the question you are asking is: “When did Italians start to identify more with their national identity rather than the local one?” I am not sure it has happened yet, and it might never happen, but I will try to give you a more satisfying answer.

As you can see the sense of national identity was already quite strong in the educated and wealthy Italians before the unification, but it is hard to gauge what the average less wealthy Italian that lived in rural area though. We know however that few people before the unification spoke “standard Italian”. A unitary language and national identity are not necessarily as related as one might think. Many Italian patriots during the “Risorgimento” spoked Italian but also spoked and cherished their local languages. However not being able to speak or read standard Italian does make people less able to interact with a common Italian culture. The Italian unitary state made many efforts to ensure that everyone could speak and read Italian, some of them misguided, however for a unitary language spoken and understood by everyone we will have to wait the for the introduction of television in Italy.

I can’t reply for Germany, but if you don’t have any luck here you might want to ask on r/Germany.

However, for a first-hand understanding of how Germans thought of themselves and Germany one might want to read correspondence of pre and post-unification period. I would suggest Frederick the Great and Voltaire.