The most likely reason for a brush with the law is if you have to report a theft. If you do have something stolen and you want to claim it on insurance, you must make a statement to the police; insurance companies won't pay up without proof of a crime.
The Italian police is divided into three main bodies: the black-clad carabinieri; the polizia, who wear navy blue jackets; and the guardia di finanza, who fight tax evasion and drug smuggling. If you run into trouble in Italy, you're likely to end up dealing with either the polizia or the carabinieri. If, however, you land a parking ticket, you'll need to speak to the vigili urbani (traffic wardens).
The legal blood-alcohol limit is 0.05% (0.5g/L), and random breath tests do occur. Penalties for driving under the influence of alcohol can be severe.
In general, your embassy should be able to provide a list of local lawyers, interpreters and translators.