The question of who, exactly, speaks Indonesian in the world may not be one you woke up with a burning desire to see answered - but then you're not a legal translation professional who gets paid, either directly, or indirectly, to know these things.
Well, in all honesty I don't actually get paid to know these things either, frankly. But all it takes is for me to note something interesting about a language and I'm off to the races as far as research goes, because I find all of this fascinating. In this case I noticed a bit of a discrepancy; when you check the numbers, there are about 23 million "native" speakers of Indonesian - and over 140 million "second language" speakers! That's an unusual spread for a language, and so I had to look into it. And now you benefit from my linguistic obsessions!
The solution to the mystery is relatively simple: Indonesian is a "standard register" of Malay, meaning that it's a version of the Malay language that is used as a standard across different cultures and borders in the area. As a result, the vast number of people who speak Indonesian have a wholly different "native" language that is often unique to a very small area where they live, and Indonesian is used as a lingua franca across the wider area. So Indonesian is spoken very widely, but is still considered a second language officially.
This may be changing; education standards in Indonesia and Malaysia have improved strikingly over the past few decades, and the percentage of the populations of those countries that speak Indonesian is fast approaching 100%. As literacy and language mastery of Indonesian rises, it becomes less a lingua franca used by incompatible cultures and more of a true standard language - especially as smaller regional languages fade away. For example, Javanese was once a widely-spoken language in the area, but the last Java-language newspaper ceased publishing 75 years ago, despite still having 85 million speakers in the world - because when people go about their business today they will speak and write Indonesian instead.
Who Speaks Indonesian
As a result the speakers of Indonesian are quite varied. Obviously, the people of Indonesia and Malay speak it. It's also an official language of Brunei-Darussalam. But that's not the whole story, because you'll also find plenty of Indonesian speakers here in Australia, where the language is one of three "Asian target languages" taught in schools in an effort to make the next generations of Australia more multi-lingual. In fact, Indonesian is the only foreign language taught at the school my daughter will be attending.
Due to its official status in Indonesia and Malay, Indonesian is actually one of the most spoken languages in the world even if the statistics do not officially show that, and its use is becoming more widespread with each passing year due to a single factor: Education. There are few better examples for the impact that good educational programmes can have on a language than Indonesian, in fact.
Image courtesy withapinkie.blogspot.com