Indonesian is one of the most difficult languages to learn. The grammar may be comparatively easy compared with English, but the socio-linguistics is a different matter altogether. Indonesian is what is sometimes termed a 'high-context'' language. In overly-simple terms, this means that, in spoken conversations, Indonesians do not use as many words to get their meaning across as speakers of 'low-context' languages such as English and Dutch do.
The difficulty for learners is that Indonesians have an uncanny ability to communicate meaning through 'unspoken' language. In essence, what is 'not' said conveys an awful lot of meaning. Therein lies the difficulty of Indonesian. That, coupled with the fact that an awful lot of ideas are worded in ways that are not immediately obvious to English speakers. It is not simply, as one person I heard mistakenly claim, a matter of putting English phrases into Indonesian.
This all becomes much more apparent the more you start getting beyond superficial 'selamat pagi, dari mana? Saya dari Australia.'- type conversations and trying to have more deeper engagements with Indonesians, especially if you are among a group of them rather than one-on-one. I've been in situations where conversations around me, that I am included in, go completely over my head. Not because I don't understand the words - I do - but because what is 'not' said throws me off. I understand every word, but I have no idea what they're talking about!!
Oh, and for the love of krupuk...please please please stop calling Indonesian 'bahasa'.