The accepted language of Bali is Bahasa Indonesia, although there is another language on the island called Balinese. 

The Balinese language is a completely different language from Bahasa Indonesia.  It has many levels, based on the Hindu caste system, of which Bali is 90% Hindu.  The Balinese caste system requires that different vocabularies be used according to differences in rank.  This means a low caste peson uses formal high Balinese words in speaking to a person of a higher caste, while the latter will answer using the low vocabulary; you speak "up" to a person of higher status, who speaks "down" to you. 

All very confusing and formal to an English speaking person.  Fortunately, English is taught in schools and nearly everyone speaks at least a little bit of English.

On the otherhand, Bahasa Indonesia is a wonderful and rich language which is very "user" friendly.  The first thing I recommend to anyone interested in learning the language is to learn the alphabet.  Indonesian uses the same 26 letters as English, but some of the letters are pronounced differently.  Unlike in English though, they are almost always pronounced the same way, with each letter being sounded out when the word is said.  So, if you know the alphabet, you can pretty much sound out any word you see written in Indonesian.  

By learning a few words, one can easily grasp some very simple concepts and be able to "communicate" with the locals just by being creative. 

For example, consider the following:

mata = eye
hari = day
mata hari = sun, or literally eye of the day, which if you think about it, that's what the sun really is!  

Another example:

jari = finger
Ibu = mother
Ibu jari = thumb, or the mother of the fingers

See what I mean?  Something else that makes the Indonesia language so friendly is the mininal use of pronouns and plurals.  For instance, the word saya is used for all of the following words: I, me, my and mine.  If there are many of something just repeat the word....buku is book, buku buku are many books.

I have found the Balinese to be very tolerant of foreigners attempting to learn and speak Indonesian.  I have yet to find anyone unwilling to exchange a lesson in English for a lesson in Indonesian.  Children are the best and most fun of teachers.  When you make a "mistake", a sly smile crosses their face before they correct you.  If you stop and think about it, it is very empowering for a six year to old to be "teaching" an adult something.  

I could go on and on, but if you are really interested in learning the language contact me and I will send you some recommendations of books and teaching aides that I have found particularly useful.