If you are going to study in Indonesia, you will need to apply for a student visa (KITAS). This can be done at the Indonesian embassy in your home country. You should first apply for a social visit visa, and apply for a student visa when you arrive in the country. The student visa is valid for one year, and can be renewed each year up to four times. To apply for the social visit visa, you will need to provide a copy of your passport, a copy of your most recent transcript and diploma/qualification, colour passport photos, proof of financial means, proof of good health and health insurance and acceptance and sponsor letters from your chosen institution.
The official language of Indonesia is Bahasa Indonesian. Across the islands however, there are over 700 recognised languages.
Whilst English is spoken in the bigger cities, and is used as a teaching language at institutions, you will not find an advanced level of English outside of these major cities. Before you move to Indonesia, it is worth learning some basic phrases so that you can get around in your first few weeks. When you have spent some time in the country, you will find that you have picked up more of the language than you expected to, make sure to utilise that skill and communicate with the locals and other international students.