You might be surprised. Half of us were either born overseas or had at least one parent born overseas. A little under a third of us have English as our second language. That doesn't mean that two thirds of us only speak English - only that English is our 'home' language.

I know there's a lot of multiculuralism in the USA also, but I don't know whether those percentages compare.

Source: https://www.abs.gov.au/ausstats/abs@.nsf/lookup/media%20release3