English is the main language spoken here but when you travel to places like Wales, you will also hear people speaking Welsh. In coffee shops or restaurants, I have occasionally heard people speaking French or Italian. The U.K. is a common tourist destination for other EU citizens.
The Great British Pound (GBP or £) is the local currency here. One GBP equals about 1.31 USD (United States dollar) and 1.14 euro. You will find Queen Elizabeth II on all printed bills with an insignia that says 'Bank of England.' Similarly to the way we have pennies, quarters, nickels and dimes in the U.S., the U.K. has pences, and they come in different sizes. Sometimes I hear locals refer to the GBP as quid, and they will use expressions like "That will be twenty quid."
A bottle of water costs between £1 to £2 depending on the brand. That is the equivalent of $1.31 to $2.63.