Australia has no official language, although English is the primary language used in this country, it has become the de facto national language. In 1788, there were about 250 separate Aboriginal languages spoken in Australia, plus dialects. Today, only two thirds of these languages survive and only 20 of them (eight per cent of the original 250) are still strong enough to have chance of surviving. In addition to these there are also the languages of immigrants from Europe, the Middle East and Asia. The other languages that co-exist in Australia are Greek, Italian and the Chinese language.
Australian English is a major variety of the language with a distinctive accent and lexicon. Grammar and spelling are similar to that of British English with some notable exceptions. Australians have their own styles and characters in using the language, vocabulary, pronunciation and accent. Though Australians speak English, they have their own special words and phrases called strine. Australian Strine consists of words and phrases which have different meanings from other English (like American or British). It also consists of words that Australians have either made up themselves, or they have borrowed from Aborigine words or from slang used by early settlers. Like most cultures, Australia has its own share of slang words, metaphors and phrases that distinguish its identity from other English speaking countries.
Sources: University World and Wikipedia