English and Hawaiian are the official state languages. At one time, the number of Hawaiian speakers had greatly diminished, but a tremendous renaissance of Hawaiian culture has taken place over the past generation or two: Today, thousands of people study the Hawaiian language and other aspects of Hawaiian culture, and there is even a K-12 Hawaiian immersion school system within the the public statewide Department of Education.
Hawaiian is closely related to the other major Polynesian dialects: Tahitian, Maori, Marquesan, Rarotongan, Samoan and Tongan. Although it is not necessarily mutually intelligible with these other dialects, many Hawaiian words and grammatical concepts are identical or nearly identical with the other dialects.
Hawaiian is also sometimes recognized around the world as the language with the fewest letters in its alphabet: a, e, i, o, u, h, k, l, m, n, p, w — 12 in all, although there's actually another consonant sound, the glottal stop [such as in the middle of the English slang term huh-uh, meaning 'no' and sometimes spelled uh-uh], sometimes represented by the 'okina or inverted apostrophe.
Most Polynesian languages, including Hawaiian, also have longer sounding vowels, sometimes marked with a bar or macron above the letter [here with a European-style umlaut, since most computers do not normally include macron options] or what the Hawaiians call a kahakö. These should not be confused with the bar or macron that is used to differentiate an English "long" vowel from a "short" vowel, as in the words "hate" and "hat," respectively.
Hawaiian words with lengthened vowels have different meanings than their counterparts with regular vowels: For example, kala is a type of fish, kalä means 'the sun,' while kälä means 'dollar' or 'money.' English vowels can also be lengthened in pronunciation, but that just changes the emphasis and not the meaning of the word.
A pronunciation problem has arisen over the years because when early Christian missionaries first devised the Hawaiian alphabet, almost everyone spoke the language and so they often did not indicate the inverted apostrophe for the 'okina or the macron bar of the kahakö in writing: Native speakers already understood the difference, say, between kala and kälä by context.
As the years went by and the number of Hawaiian language speakers greatly diminished, however, many people didn't know about the 'okina sound or long vowels. For example, Kaua'i became Kauai (as in 'cow-eye') and O'ahu became Oahu. Along with the rest of the Hawaiian renaissance, people and institutions such as media and government are becoming more sensitive to including the 'okina and kahakö in written Hawaiian; so don't be surprised to see both Waikiki and Waikïkï or Lanai and Läna'i...and try to pronounce them in the old Hawaiian way.