Learn Bahasa Indonesia and Bahasa Malaysia.
Bahasa Indonesia is the national language of the Republic of Indonesia. While it may be technically possible for foreigners to live in Jakarta without learning/speaking Bahasa Indonesia, it is highly recommended that you obtain a working knowledge of the Indonesian national language. An inability to communicate in Bahasa Indonesia will cut you off from the mainstream of society, and dealing with those Indonesians who dont speak your foreign language will be very difficult. By not learning the language, you also deny yourself the rich cultural experience of fully communicating with those from another culture.
To get you started and introduce you to the Indonesian national language, there are some 60 chapters in the course, you can hear the pure accent of the vocabularies, phrases and dialogs in the app.