The official language of Indonesia is known as Indonesian or 'Bahasa Indonesian'. Indonesian is a standardised dialect of the Malay language and was formulated at the time of the declaration of Indonesian independence in 1945. Malay and Indonesian remain very similar.
Although the official langauge, in reality it is most of the population's second language. Due to the sheer size and fractured, island make-up of the country most people speak regional dialects such as Minangkabau or Javanese. These will usually be spoken at home and in the local community but at work or at school Indonesian is used.