There are 240 million people across many cultures and ethnicities in Indonesia and countless dialects you might hear. However, the official language is Bahasa Indonesian - usually called Indonesian by westerners.   English is widely spoken and used in education and business. But, in rural spots, people aren't as likely to speak English, plus it's much more respectful to have learned some of the local language.   If you move to Indonesia and make an effort, you will find people very warm and welcoming and happy to help you finesse your Indonesian.