Chile has a well-established connection to the U.S.; but English is not necessarily taught in every school. German is a very common second language, especially in the south. French is also common. And South America is full of resources, so in some ways, a second language isn't needed – Spanish goes a long way. You should not assume everyone will speak English.
Many hotel owners and managers will speak English. They understand the clients are from other parts of the world. Most people in customer service at the airports will also speak English, even if they are shy about it. Restaurants will be 50/50 at best. Taxi drivers can probably quote movies. So if you are going to rely on English you will not get very 'deep' into the culture. Learning some Spanish will go a long way.
Communication is not entirely verbal. Actually, most of what we communicate is non-verbal. The person you are "talking" with may not understand a word you are saying; but they will certainly form an opinion on whether you are: in a hurry; patient; very pissed off; clueless; happy; or in genuine need of help. How you communicate is more important than what you communicate.
Here are some things that are very commonly seen – and very embarrassing to watch:
– Speaking like a cave man. Simple sentence structure is helpful. "I want to go to the museum" is better than "I would like to take a stroll to your most famous house of art." But, "Me visit museum" is not even English and doesn't help anyone.
– Yelling. Don't yell. The person isn't deaf – not yet anyway. They don't understand. And all they think is that you are a typical loud American and they would like you to leave.
– Trying to convey the "importance" of what you need to do or who you are. Quite frankly, no one cares. Your poor planning does not constitute someone else's emergency.
You do not need to speak perfect Spanish to travel to Chile. However, your experience will be greatly enhanced by a willingness to learn, practice and be patient. Even if you only speak three words (hola, por favor and gracias being good words to start with) use them every time you get the chance. Never say hi, please or thanks. Eventually they will be second-nature and you can focus on other words or expressions. Be willing to make mistakes. It's actually incredibly endearing. People appreciate the effort and will return the favor.
Go to Chile because of the differences. Learn a little of the language and experience the culture. It is an amazing opportunity to get off the beaten path and broaden your horizons.