I spent 2 weeks there doing the ring road. Everyone we met spoke perfect English. I mean absolutely perfect. We were talking to our server at a restaurant in a tiny village in the north and asked him if he had ever been to the USA since his accent was a perfect standard USA accent. He said he'd never even left his village to visit Reykjavik!
Language was a non-issue for us. English proficiency was high. For those who don't speak English, if you're friendly enough, you can point to what you need, plus there's so many electronic aids these days if push comes to shove, it's not an issue. Perhaps more importantly, cultural norms will be familiar to Westerners, which makes it easier.
Oh, edit - as others said, things are really quite expensive there, including food and drinks. Research before going. A breakfast of bread, butter, jam, a sausage and two sunny-side-ups can easily be 30 USD. A pint is 8-12 USD. A lunch of an unlimited soup and bread - 15-20 USD.
From the east coast of the US, it's an easy flight. Often cheap too. Or, do a stop-over on your way to/from Europe /UK.