Sukriti Acharya, 7, is shy about speaking a second language but during family car trips, Nepali is her favourite game.

"I will say 'apple'," her father Rishi says, "and she will say –"

"Shayau!" Sukriti interjects, on cue.

Sukriti is typical of a growing population of Sydneysiders – now nearly 40 per cent – who speak a non-English language at home. The family's home in Rockdale in the city's south has the biggest share of Nepali speakers of any suburb, and a large population of Mandarin, Macedonian and Arabic speakers. Just three in 10 of Rockdale's residents only speak English at home.

Non-English speakers outnumber English speakers in one in five suburbs, cementing the city's status as one of the world's most linguistically diverse cities.

Nearly 240 languages are spoken across Sydney, including 75 with at least 1000 speakers, according to a Fairfax Media analysis of Census figures.

Arabic dominates the western suburbs and is the most widely spoken non-English language, with nearly 5 per cent of Sydneysiders using it at home. Mandarin and Cantonese, found predominately on the north shore, are the next most common.

But nowhere is Sydney's patchwork of languages more vibrant than in Liverpool, which boasts 20 languages and is the city's most linguistically rich suburb.

Nearly two in five residents there speak Arabic and one in 10 speaks Serbian. Hindi, Vietnamese, Spanish and Italian are each spoken by more than 2 per cent of residents.

Yellow Rock, in the Blue Mountains, has the least linguistic diversity, with 97 per cent of residents only speaking English at home.

"Language is incredibly important because it becomes the connection to the old ways," says University of Melbourne language professor Joseph Lo Bianco.

But not every group gives language the same importance. Why some groups maintain their language depends on a constellation of factors including when, why and how people migrated, the social and political environment of the new country, and intermarriage between language groups.

"For each culture, you’ve got to make an investigation into the history and … each history is unique," says adjunct associate professor Uldis Ozolins from the University of Western Sydney.

The Dutch, for example, often abandon their language in the first generation, while many Greek immigrants still speak Greek at home even several generations later.

"The Dutch see themselves as very liberal, very cosmopolitan, very modern citizens of the world. There is no pressure to maintain Dutch," Dr Ozolins says.

The attitude contrasts with Greeks, who are conscious of being a small country with an enormous heritage.

"Greece was under Ottoman rule for nearly 400 years. The language had been actively repressed," Professor Lo Bianco says. "In the course of that history, Greek became elevated as a core value for the immigrants who came here."

Gender has played a special role in the maintenance of Filipino because unlike most countries, migration from the Philippines has been led by women – primarily maids and brides, Professor Lo Bianco says. "Mothers in particular are better at maintaining language … because they spend more time with their children and raise them in their language at home."

For other groups, the importance of other cultural markers can make the preservation of language seem less critical. Italians and Chinese, for example, place a strong cultural emphasis on food and family, while for Asian and African immigrants culture is conveyed simply by physical appearance.

And among refugees, language is often a political and cultural symbol, and a crucial part of their identity. For those fleeing occupation, language of origin may be entwined with the hope they will one day return home.

"They see [language] as part of the culture that’s been lost or that’s been threatened in their homelands," Dr Ozolins says.

Language groups are more segregated in Sydney than in Melbourne, which experts attribute to geography, income inequality and Sydney's notorious housing shortage.

Higher property prices limit where new migrants can afford to live, while the city's terrain – chopped into three parts by rivers and harbours – separates pockets of wealth from low cost, immigrant-rich areas.

"It’s a class divide … with migrants in Sydney very much being in the working class areas," Dr Ozolins says.

The percentage of Sydneysiders who speak a community language at home rose from 27 per cent of residents in 1996 to 38 per cent in 2011.

Cabramatta, which has the smallest share of English speakers (12 per cent), is one of 21 suburbs where English is the second or even the third most common language.

Unlike countries such as India, where people are used to hearing (and often speaking) different languages, the use of languages other than English in Australia – particularly in public – has historically been perceived as a cultural threat. The shift to multiculturalism in the 1970s was a turning point.

"We live in a country where unity of the state is partially based on the homogeneity of language," says Curtin University cultural studies professor Jon Stratton.

"When you have a proliferation of languages in the public domain you get an anxiety about the possible fragmentation of … the state."

Rishi says Sukriti prefers to speak English but they are maintaining her Nepali by borrowing Nepali books from the library every week and taking her to Nepali school on Saturdays.

"We always encourage her to speak Nepali at home," he says. "It's important that she remembers where she is from."