Before then, people born in Australia were British subjects. People born in Australia (including Norfolk Island, Cocos (Keeling) Islands and Christmas Island) on or after 20 August 1986 are Australian citizens by birth if at least one parent was an Australian citizen or a permanent resident at the time of the person's birth. Statistics do not exist as to the number of Australians who currently are dual citizens. In 2000, it was estimated to be 4 to 5 million people. The current Australian resident population is estimated at (02 2020). This does not include an estimated 1 million Australians living overseas, but it includes Australians born overseas. There are an estimated 1 million Australians (approximately 5 percent of the population) residing outside Australia. The Trans-Tasman Travel Arrangement facilitates open migration to and from New Zealand. Although Australia has no official language, English has always been entrenched as the "de facto" national language. Australian English is a major variety of the language with a distinctive accent and lexicon, and differs slightly from other varieties of English in grammar and spelling. General Australian serves as the standard dialect. According to the Australian Bureau of Statistics (ABS) 2016 census, English is the only language spoken in the home for close to 72.7 percent of the population. The next most common languages spoken at home are:   A considerable proportion of first- and second-generation migrants are bilingual. Over 250 Indigenous Australian languages are thought to have existed at the time of first European contact, of which less than 20 are still in daily use by all age groups. About 110 others are spoken exclusively by older people. At the time of the 2006 census, 52,000 Indigenous Australians, representing 12 percent of the Indigenous population, reported that they spoke an Indigenous language at home. Australia has a sign language known as Auslan, which is the main language of about 5,500 deaf people. Australia has no official religion; its Constitution prohibits the government from establishing one, or interfering with the freedom of religion. Australians have various religions and spiritual beliefs. Majority (52.1 percent) were Christian, while 30.1 percent of the population reported as having no religion, of those reporting as having religious affiliations according to the . As in many Western countries, the level of active participation in church worship is lower than would be indicated by the proportion of the population identifying themselves as Christian; weekly attendance at church services was about 1.5 million in 2001, about 7% of the population (21.5 million) that year.