In tourist centers like Cusco and Machu Picchu or in high class hotels, English is spoken. If you intend to visit other sites, especially in the countryside, you'll need Spanish. Like every other Latin American country, Peruvian Spanish replaces vosotros (and its 2nd-person plural conjugations) with ustedes (3rd-person plural). For example: ¿Cómo están? instead of ¿Cómo estáis?. South American Spanish likes diminutives (gringuito is more affectionate than gringo).

If you learn languages easily, try to learn Quechua, the language of the Incas. It will be highly appreciated in the countryside of the Sierra, where many indigenous speak it as a first language. On the Altiplano, the unofficial language Aymara is widely spoken. Aymara was the language of the Tihuanacu culture.

Peruvian Spanish, particularly in the Sierra and jungle, is pronounced much more clearly than European Spanish and Spanish from other Latin American countries, especially Mexico, Colombia and Chile. People don't tend to speak too fast, although in coastal areas, especially Lima, people speak considerably faster than in other areas, and they also use slang quite liberally. On the whole, Peru is a good and cheap place to embark on Spanish courses (once you are there).

Some slang terms:

Chevere, Bacan cool.

Chela, a beer.

Me da colera, Me llega, it pisses me off.

Ya, right, sure (sometimes "ok" or "yup").

Loco ,crazy person.Usually said in a friendly manner, also means "mate, friend, buddie"

Tombo, is cop (and cops don't like hearing it).

bamba counterfeit goods, bad or illegal products

Money is often refered to as plata (as in silver). Eso cuesta mucha plata = that's expensive.

Some slang terms come from Quechua:

Que pinya: means 'what bad luck' even though pinya in Quechua means 'coraje' or in English 'infuriating'.

tengo una yaya: means 'I'm injured'. In quechua 'yaya' means injury. And yawar means blood.