What languages are spoken in Thailand?

The main language spoken in Thailand is Thai.

Different parts of Thailand have different dialects and different ways of speaking, so it can be quite difficult to understand Thai speakers from another part of the country.
Hill tribes and other ethnic groups have their own languages; for instance there are villages of Chinese settlers in Thailand where little Thai is spoken, or on the islands where sea gypsies have settled. English is the most common second language, and many Thais have studied some level of English either at school or through practice with foreign friends.

Is English widely spoken?

In Bangkok, where the major business and commercial transactions are held, English is widely spoken, written and understood. Further, in most hotels, shops and restaurants of major tourist destinations, English and some European Languages are spoken, written, and understood.