Indofag here
>>8
not entirely true
Javanese have more native speakers than Indonesian, but almost everyone in Indonesia speaks Indonesian as a second language, even Javanese people. If I was to pick up a phone and dial a random Indonesian number, I can be 99% be sure that the person at the other end can understand Indonesian.
>>10
inorite? Most people here speaks shitty Indonesian, even most of the educated people. I felt ashamed of my countrymen when a foreigner speaks better Indonesian than the average Indonesian.
To OP, I don't know where Indonesian would be useful outside of Indonesia, Malaysia, Singapore, East Timor, Brunei.
>>7
I disagree
learning Javanese would be less useful than Indonesian. Indonesian is technically a dialect of the Malay language. If you know Indonesian, it wouldn't be hard to learn other Malay dialects. The difference between Indonesian and Malaysian is mostly in pronunciation and accents. Written down they're the same language with slightly different vocabulary and minor spelling difference.