On our most recent trip we travelled through three different languages: French, Portuguese and Spanish. In Australia, none of these languages are routinely taught in schools. In high school you might do one semester each of a few languages compulsorily, but other than that, languages are electives. Some primary schools offer a language as a pull-out subject. However most Australian schools do not have compulsory long-term learning of any language (other than English!).
What this means is that many Australians who are not immigrants and whose parents are not immigrants, do not speak any other languages other than English. Some will have a smattering of high school French or German or Japanese.
However, it is common courtesy to learn at least a little of the languages you will encounter on your holiday. My husband took several terms of French lessons at our local community college to revive his (actually excellent) high school French. Because of his efforts in French we were treated with great courtesy in Paris - even though Parisians are notorious for being rude and aloof.
We and our kids learned "please", "thank you", "hello" and "goodbye" for each language we encountered. We encouraged our children to use these words in the local language at every opportunity.The locals really appreciate people making an effort to speak some of their language.
In parts of Europe you can often find someone who will speak some English, but you can't count on it! Why should they speak English when it isn't their local language? They certainly don't have to! I can't really imagine what it would be like to come to Sydney from a French-speaking country and hope that you'll be able to converse in French. Its just not likely to happen.
It does also say a lot about language teaching/learning in Australia that it is such a low priority for us to learn other languages...
So, before you go, or even as you travel (if you have lots of different languages that you will encounter along the way) learn the basics and teach your children. The best way to learn another language is through immersion, and the best place to do that is a country where it is the local language.