I am an aging hyper-polyglot, and I periodically do maintenance of little-used languages in order to keep my bragging rights
In the last month I have been restudying Bahasa, which I learned and used once, in 2005-2006.
I am also a cognitive psychologist who knows a bit about consolidation research. In order to activate the retrieval path, I first go through all my previous materials and then find more to progress. Slow-down audio is indispensable for consolidation and retrieval.
I would have normally started with Pimsleur and gone on to FSI. But Pimsleur had not yet done bahasa, and to the best of my knowledge there is no Foreign Service Institute course. There may be peace corps materials, but they are usually sketchy and focus on words rather than grammar.
So in 2005, I started with Edward S. King's Speak Malay and write Malay, printed around 1986. These work very well for Bahasa. A friend took the trouble to read them on cassette.
Then I went on to 'teach yourself indonesian', and to an unknown method from the 1970s that had audio. A few years ago I digitized all cassettes. (The books are out of print, but can still be found on ebay sometimes.
Then I went on to Malcolm Mintz's readings in Indonesian and Malay and a further Listening Comprehension - selections from Malaysian and Indonesian history. These come with audio files. Malcolm Mintz was a professor in Australia, I believe. He is retired but still selling the remaining prints of his excellent books. I can give an email address to those who need it.
These materials, which I studied over about 4 months, provided me with most of the vocabulary I needed to deal with my World Bank job at the time. Bahasa does have grammar of course, but one can progress into vocabulary and content quickly. (Unlike Swahili or Albanian, where one is stuck in basic grammar for quite a while.)
Some of these materials are hard to find or just in my hands. I have therefore deposited the 'teach malay' and write malay audio at the fis-courses.yojik.eu website. Also that unknown method I have with its audio files. The Edward King boosk are clearly out of print, and if in principle one could photocopy them for the sake of knowledge. But the glue breaks easily, so I bought a second set from ebay.
In 2017, someone posted a long set of sentences in the more colloquial dialect. The books above clearly don't deal with it, except in one lesson at 'teach yourself indonesian'. So today we must learn that.