There may not be a language barrier (well, kind of) but life in the UK is different than life in the US.
Weather
One of the main features of the British climate is its variability. This means that even in summer there can be spells of cold, wet and windy weather. On the other hand it can mean that winters may be short and not very cold. In general, the west of the UK is wetter and milder than the east. In Scotland you can expect to see some snow in the Highlands and Glens, while in the south snow is often not seen at all.
In any event, take warm clothes and clothes that can be worn in warmer weather. Layering is the key to being comfortable in the UK. And yes, of course bring an umbrella!
Public Holidays and Festivals in the UK
Christmas Day
Christmas is celebrated in basically the same way it is in the States. However, December 25th and 26th (Boxing Day) are both national holidays. Families congregate on Christmas Day and exchange gifts and eat copious amounts of food. There is no public transport on Christmas Day and limited transportation on Boxing Day.
Boxing Day (December 26th)
The day after Christmas is known as Boxing Day, which takes its name from a former custom of giving a Christmas Box - a gift of money or food inside a box - to the deliverymen and tradespeople who called regularly during the year. This tradition survives in the custom of tipping the milkman, postman, 'dustmen' and other callers of good service at Christmas time.
New Year's Day
January 1st is also a public holiday. In Scotland however, New Year's Eve is known as Hogmanay and is an even more festive occasion than Christmas. Scotland also considers January 2nd a public holiday.
Easter
This public holiday extends from Good Friday to Easter Monday. Chocolates and decorated eggs are given as gifts and there are Easter parades. On the Thursday before Easter, the Queen visits a different cathedral each year to give a symbolic gift of money (Maundy money) to local inhabitants.
Guy Fawkes Night
November 5th is not a public holiday, but all over Britain there are bonfires and fireworks to celebrate the foiling of the Gunpowder Plot on Parliament in 1605.
The public holidays in the UK are as follows:
January 1st, New Years day
Good Friday, (Friday before Easter)
Easter Monday, day after Easter
The first Monday in May
The last Monday in May (Bank Holiday)
The last Monday in August (Bank Holiday)
Christmas Day, 25th December
Boxing Day, 26th December
Scotland has an additional Public Holiday on the 2nd of January and Northern Ireland has an additional Public Holiday on the 17th of March. The UK's diverse population means that many other religious holidays are recognized including Ramadan and Yom Kippur.
British schools also have about three weeks off at Christmas and Easter, plus around six weeks from mid-July to the end of August.