I looked up-- no, I am looking up an Indonesian Language lesson thing, and I noticed something rather curiously funny.
Ya. Yes. (often means no)
I'm not sure what they're shooting at here, but I'm pretty sure I don't say yes to say no. Except when I say, "ya, terima kasih," which literally means yes, thank you but can also mean I know, but I'm not taking it anyway.
More on things they don't tell you on those nifty sites, there are the colloq of certain words like "I" and "you".
I can be Saya (formal), Aku (informal), or Gue (colloq). This doesn't mean that it's disrespectful (well, quite), but you'll certainly look out of place around adults. Mostly teenagers use this, and that's only around their peers, so it's unlikely that anyone will address you as "Loe/Lu" (colloq of You).
Of course, considering that Indonesians also takes in other languages in the area like Sundanese or Javanese, you'll be meeting lots of words they don't teach you in formal courses. Mbak, Beta, Ndak, etc, etc.
In other words, you'll probably come back all confused anyway. But don't worry, most of us are pretty understanding, and we like and admire tourists anyway. So forget about that other languages and just enjoy your vacation.