Ah I see... that's that idea out the window then.
The language localization is done by way of database language tables. When you change the site language, this is done in the code by switching to use a different table. Nothing at all is done with the URLs - they always remain the same no matter what language you're looking at.. this is my problem. I need language specific URLs - so a subdomain, top level domain, language parameter, etc.
I think I'll have to go back to looking at 2 lots of website files (one for each domain), looking up to the same backend database. It doesn't seem very efficient doing it like this though and I was hoping to be able to just manipulate the URLs instead.