THE BAHASA LANGUAGE
As mentioned in the article about Malay, both of them are very closed. This, due to the fact that Bahasa is a variant of Malay. That has been used as a lingua franca in the multilingual Indonesian archipelago for centuries. The country being the fourth most populous in the world, its language ranks among the main one in the world too.
Also, note that Bahasa is not much hard to learn. Indeed, there is no tense, no gender, only one form of pronouns and we pronounce all letters.
The main dialect in the region
The fact that this language reaches hundreds of millions of people implies that there are many dialects. We know some that are quite famous. Most of locals are fluent in at least one of the more than 700 native local dialects. Among the main ones are Javanese, Sundanese, and Balinese. However, Bahasa remains the official one used in media, school, state and legal field, etc. Of course, Bahasa is one of these dialects but the main one. So, the term Indonesian actually includes all dialects spoken in this part of the world.
Bahasa is a standard variety of Riau Malay, a form of Classical Malay which emerged in the royal courts of Johor and Malacca Sultanates. For about 500 years, North East Sumatra used Malay as a lingua franca. Thus, linguists consider Old Malay as its parent.
Thanks to trade contacts carried on by various ethnic peoples at the time, Old Malay widely spread.
Bahasa shares the same basis than standard Malay. However, it differs from it in different aspects, like the way how to pronunce it or in terms of lexicon. This, mainly due to Dutch and language of Java which affected the latter quite a lot.
Malaysian Malay claims to be closer to the classical Malay of earlier centuries. However, some doubts remain. Indeed, linguists still ignore whether High Malay (Court Malay) or Low Malay (Bazaar Malay) was the true parent of Bahasa. On one way, the court of the Johor Sultanate used High Malay, still spoken in Riau Lingga. On another hand, we commonly found Low Malay mainly in markets and ports.
The Dutch era
When the Dutch East India Company (VOC) first arrived there, the Malay language was a significant language in trades and politic. However, as it was limited to mercantile activity, locals never fully used it.
Anyway, the VOC used Malay for trades. But the VOC went to bankrupt and the Batavian Republic took control of the colony from 1799. Then, Dutch stopped to spread in the colony. And this, while Dutch chairs themselves were reluctant to promote Dutch compared to other colonial regimes. Thus, Dutch remained the language of a small elite. That is how, in 1940, only 2% of the people could speak Dutch. But during the colonial era, Malay absorbed a lot of Dutch lexicon. And so, Bahasa too.
Such a strange Dutch method
The movement that gave Bahasa its status of national language, rejected Dutch from the outset.
But the fast erasure of Dutch was not usual compared to other colonized countries. Indeed, most of the time, locals still use the colonial language. This, in different fields of importance such as politics, school, high tech, etc. Finally, both Dutch policy itself and nationalists explain the ease with which Indonesia threw away the language of its former colonial power. In marked contrast to French or Spanish, which made efforts to assimilate the native people at best, the Dutch did not attempt to spread their language.
Finally, the only fact to always refuse to provide education to locals simply blocked its spread. Actually, they just fell into their own trap. This, because the Dutch wished to prevent locals from getting a higher social status via the Dutch culture. As a result, until the 1930s, they allowed Malay to spread quickly accross this part of the world.
At that time, Dutch covered nearly all aspects, with official forums requiring its use. In parallel, the use of Bahasa as national language was agreed from 1928 as one of the tools in the independence struggle. However, they wrongly did not think Bahasa strong and serious enough. Thus, some local protests led to the use of Bahasa from 1938. It was then already too late when they tried to stop its spread in schools. Also, Japan forbade Dutch when they conquered the country. Only a few years later, locals themselves formally abolished it in favor of Bahasa.
Obvious or not
Although a very small minority, the country chose Bahasa as its official language as soon as it god independence in 1947. At that time, 45% of the locals spoke Javanese and 15% spoke Sundanese. Logically, Javanese was then the main language of politics and economics, and the language of the court, religion and literary tradition.
However, it lacked this scope to unify the country. Indeed, with thousands of islands and hundreds of dialects, the country was looking for a national language. And this, so that most can speak it and that it does not favor one ethnic group or another. In reality, the Bahasa language did not appear suddenly. The population had known it in part for almost 1,000 years. Also, it was the language of the sultanate of Brunei and of future Malaysia, where nationalists had claims. All that finally allowed it to establish itself.
Thanks to a language program, Bahasa became the language of politics, education, and nation building in general. Thus, it became one of the few success stories of a native language which overtook its colonisers.
Now, it is still the language of national identity, education, literacy, modernization, and social mobility. This, despite the fact that most locals use it as a second language.