Errr...if I'm not mistaken, bahasa was originated from the Malacca Region (Malaysia, West Sumatra, Riau, etc). So if you noticed that Malay and Bahasa are almost similar, since it comes from the same root. Around 700-800 AD (?) there was a big kingdom (Sriwijaya) whose capital in Palembang (sumatra) and whose area covered almost as big as Indonesia now (plus Malaysia). Sriwijaya was the centre of culture also, at that time the malay culture was spreading fast, so does the language.Also people from the Malacca region are usually traders, so they travelled to almost into every parts of Indonesia.

So anyone want to continue my story ?