Sure. One that springs to mind, for me, is Pompeii. Pompeii's exact origins are disputed but prior to its subjugation by Sulla's nephew during the 1st century BCE 'social war', Pompeii was a Greek city populated also by 'Oscans', who spoke and wrote in the Oscan language, as well as Greek-speaking peoples.

The mass-adoption of Latin by inhabitants of Pompeii happened for obvious reasons (i.e. Roman subjugation), helped by the settling of a colony of Roman veterans in the town after the end of the social war (Sulla's nephew among them). The Oscan culture was still present, if not as extensively, until the extermination of the town in 79 CE, though. Surviving examples of Oscan graffiti are rare (source: Graffiti and the Literary Landscape of Roman Pompeii, by K Milnor ).

Several. One example is linguistic shift. Look at old english vs middle english vs modern english. Old english is a harsh germanic language closer related to nordic languages than current english. The norse brought new words and syntax rules to the base language. When the normans invaded they brought their latin based norman tongue (a early version of french) and "corrupted" the germanic tongue with latin influence. The higher classes spoke french and relegated the anglo saxon tongue to the lower classes. For example Richard the lion hearted didnt speak a single word of english. Generations of the nobles speaking french and peasants speaking anglo saxon english caused the two languages to meet in the middle. Another example is egypt. You start off with ancient egyptian, then move to greek when alexander and the Ptolemaic dynasty took over, they kept speaking greek after the romans took over along with the coptic tongues spoken in the area. After the arabs took the land of the pharaohs their language sorta took the spotlight. Languages change all the time, it just rarely happens all at once. The romans did their part though to change the language of lots of cultures, like the gallic celts or the iberians.