According to the bottom half of
this page an overseas marriage is generally recognised assuming that it would be a legal marriage in Australia.
For arguments sake, if a 21 year old married a local 15 year old in a country where a 15 yo could marry then it would not be recognised in Australia. The first example above (second wife) would not be recognised in Australia as Australia will only allow one husband/wife.
The second example above (happytimes) would appear to be recognised as a legal marriage under Australian law (assuming there was legal paperwork for the traditional marriage) but an overseas marriage does not appear to guarantee entry to Australia for the overseas partner. Immigration is handled separately. If "traditional wedding" meant it was all verbal and there was no supporting legal documentation then that might be an obstacle.
happy2 said:
...If a sea captain can marry you in International waters...
I don't believe a captain of a ship actually can.
This is the first page I found about the topic and it appears that it's just a myth. A captain is no more entitled to marry people than the postman. Other sites are in agreement, such as
About.com,
abc.net.au and even
TVTropes.com.
The common theme appears to be that although planned marriages can and do happen on ships (for the romantic value), the key there is "planned". A captain can only perform a marriage if he/she also happens to be an ordained minister (or other role with specific authority to perform marriages).
Thanks happytimes, your comment prompted me to do some research and I learned something new. I assumed captains could perform marriages as well.