Spanish is the official language of Chile. English is quite widely spoken in Santiago and the government wants to turn Chile into a bi-lingual country within 20 years. Although this is unlikely to happen, more and more people are learning English. Outside of Santiago and Viña del Mar, it is very hit and miss that you'll find English speakers. Younger people normally know a little and there will always be someone around who can speak a few words. It is advisable that you learn Spanish as it makes every day life much simpler and less stressful. However, depending on where you live it might not be essential that you speak excellent Spanish. A few words will often do.

Spanish is a fairly easy language to learn and it is easy to reach basic conversation level very quickly. Chilean Spanish can be difficult to understand at first for people who have learnt Spanish before arriving as it is spoken very quickly and with a lot of local slang but you quickly adapt.