Most facts about the Indonesian language are trivia. These fifteen are not, because each one changes something about how you should learn it.
Several of them come from the eighteen minutes below, which is the best short survey of Indonesian grammar on YouTube, and one of eleven channels worth your time. It is denser than anything on this site and it uses IPA throughout, so it rewards a second viewing once you have a few lessons behind you. Where it and this site disagree, I say so, and that happens once.
The Indonesian Language (Bahasa Indonesia) is Awesome, Here's Why! by LingoLizard, whose own sources are Sneddon's Understanding Indonesian Grammar and Michael C. Ewing's chapter on colloquial Indonesian.
1. Most people who speak it learned it second
Indonesia has the second-largest number of languages of any country on earth, somewhere around seven hundred. Indonesian is the bridge between them, which means the majority of its speakers grew up in Javanese, Sundanese or Balinese and learned Indonesian at school.
Why it matters to you: you are not competing with lifelong native speakers. You are joining a country of people who all learned this language deliberately, which is exactly why it was kept simple, and exactly why nobody will mock your accent.
2. There are officially two Indonesians, and they have names
Bahasa baku is the standard language: government, news, textbooks, school. Bahasa gaul is what people actually speak, on the street and online.
This is not a formal-versus-slang spectrum like English has. It is the organising fact of the language, and it is why a learner can finish a course and still not follow a conversation. Almost every app teaches you baku without mentioning that the other one exists.
3. The plural is sometimes written with the digit 2
Indonesian makes plurals by saying the word twice: buku book, buku-buku books.
Informally, people write that repetition as a 2. You will see buku2 in messages, anak2 for children, jalan2 for wandering about. No textbook mentions it and you will meet it on your first day of WhatsApp.
4. The most common word in the language is yang
Not a greeting, not a pronoun. According to frequency lists, the single most common Indonesian word is yang, which introduces relative clauses: which, who, that.
rumah yang besar ‘the house that is big’
yang besar ‘the big one’
It also works alone in front of an adjective, which is how Indonesians point at things in shops all day. The yang lesson is short, and learning it early pays for itself faster than another fifty nouns.
5. You count things with a word for “tail”
Numbers do not attach directly to nouns. A classifier goes in between, and which one depends on what you are counting: orang ‘person’ for people, buah ‘fruit’ for objects, ekor ‘tail’ for animals.
dua orang guru ‘two teachers’
tiga buah buku ‘three books’
empat ekor kucing ‘four cats’
And satu ‘one’ becomes se- when it meets a classifier, which is why you say seorang rather than satu orang. That same se- hides inside sebelas ‘eleven’ and seribu ‘one thousand’. The classifiers lesson has the ones worth knowing, and there are fewer than the dictionaries suggest.
6. There are two words for “we”, and the difference is social
Kita includes the person you are talking to. Kami excludes them.
Say kami when you meant kita and you have just told someone they are not invited. It is not offensive, but it is noticed, and English gives you no warning because English has one word for both.
Colloquially, kita is taking over both jobs, and in some regions it even replaces “I”. The kita and kami lesson is one of the shortest on the site and one of the most useful socially.
7. Jakarta has its own pronouns, borrowed from Chinese
Textbook Indonesian gives you saya and Anda. Jakarta says gue and lu, and those two came into the language through Betawi from Hokkien, brought by Chinese traders centuries ago.
You will hear them constantly in films, on YouTube and among anyone under forty in the capital. You should recognise them immediately and use them carefully, because they are wrong in most of the situations a visitor ends up in. Start with the saya and aku split before you go near gue.
8. The verb prefix changes shape to match the sound after it
meng- is the prefix that turns a root into an active verb, and it mutates depending on the first letter of that root.
tulis ‘write’ becomes menulis
baca ‘read’ becomes membaca
kirim ‘send’ becomes mengirim
Worse, roots beginning with p, t, k or s lose that first letter entirely: pakai becomes memakai. This is the single hardest thing in Indonesian grammar, it is finite, and it is where most self-taught learners stall. It is also the main reason Indonesian takes longer to finish than to start. Take it as a system in the affixes lesson, not as a list of words.
9. And in real speech, that prefix is usually dropped anyway
Having learned that meng- is compulsory in formal Indonesian, you then discover that colloquial speech drops it on most verbs.
mengerti becomes ngerti
membeli becomes beli
Both facts are true at once, and knowing only the first is the classic learner’s trap: you produce textbook sentences correctly and cannot decode the reply.
10. There is a whole prefix for things that happened by accident
ter- marks the accidental, and there is no neat English equivalent. It covers actions that were sudden, unintended, unexpected or beyond your control.
jatuh ‘fall’ gives terjatuh ‘to fall accidentally’
bawa ‘carry’ gives terbawa ‘to carry off by mistake’
It is the prefix you will want on your third day in the country, and colloquial speech often swaps it for ke-. The ter- lesson covers both.
11. “What is your name?” uses “who”, not “what”
Siapa nama Anda? is literally ‘who is your name’. Using apa ‘what’ there is a mistake English speakers make constantly, and it is one of the few that sounds genuinely odd rather than merely foreign.
The same logic runs through introducing yourself, where Indonesian puts the thing before the owner: nama saya is ‘name my’.
12. The textbook word for goodbye is one you should almost never say
Selamat tinggal appears in every phrasebook as “goodbye”. It is said by the person leaving, to someone staying, and it carries the weight of a departure with no return.
The video puts it more strongly, saying it implies the person is going to pass away. That is stronger than how I would put it, and it is the one claim in the video I would soften rather than repeat: the connotation is final parting, and death is one reading of that rather than the meaning.
Either way the fix is the same. Say sampai jumpa ‘see you’, which works in both directions and cannot be got wrong, and leave the other two to the goodbyes lesson. It is one of forty phrases worth having ready before you land.
13. Indonesian spelling was Dutch until 1947
Before the reform, u was written oe, so Soekarno was the same name now spelled Sukarno. The sounds now written c, j and ny were tj, dj and nj.
In 1972 Indonesia and Malaysia agreed to align their spelling, which is why the two languages look so alike on the page today. You will still meet the old system on colonial-era signs, in old family names, and in the spelling of streets nobody has renamed.
14. The vocabulary is a map of who traded there
Indonesian sits on the Strait of Malacca, and eight hundred years of shipping left their vocabulary behind:
Hokkien: toko shop, teh tea
Sanskrit: muka face, utara north, singa lion
Arabic: kertas paper, kabar news, sehat healthy
Javanese: enak tasty, gampang easy
Dutch: pos post, nol zero, lampu lamp
English: botol bottle, gitar guitar, riset research
That last row is the useful one. Hundreds of English words entered Indonesian with the spelling rewritten phonetically, which means you can often guess a modern technical word by saying the English one with Indonesian vowels. And kabar is hiding in apa kabar ‘how are you’, literally ‘what news’, which the apa kabar lesson unpacks.
15. The government added a diphthong in 2015
The official standard gained a fourth diphthong, ei, to handle loanwords. Whether ordinary speakers pronounce it any differently from a plain e is another question, and the video is honest enough to say it does not know.
This is worth knowing less for the sound than for what it tells you: Indonesian has a national language agency that actively legislates the standard, publishes the official dictionary, and coins replacements for English borrowings. Some of those coinages stick and most do not, which is the clearest illustration of the baku and gaul gap you will find.
If any of this made you want to start rather than read about starting, the beginner course begins with pronunciation and labels the register on every example, so facts 2 and 9 never take you by surprise.