It will depend how well you know the person and if they are already a friend or someone important you are being introduced to.
Informally you might use hallo or salut, slightly more formally bonjour, or quite formally bonjour monsieur/madame.
salutations
nounsalutationsvœuxsouhaits
salutation
Australians speak english, unless of corse aboriginal. so you would say seasons greetings.
Hello - Bonjour
Salutations
Joyeux anniversaire
Speak french
bonjour means good day/hello
To speak is "parler" in French.
Speak ( in English) - parler( In French )
french people speak french but they don't only have to speak french.