The download and installed worked well. I first confirmed Microsoft Office applications such as Word/Excel still use Microsoft's own dictionary. Outlook still uses your selected Apple dictionary. I find this truly weird, but it indicates Microsoft's developer teams may be separate for Outlook and the rest of Office. I was wondering if this would change but it hasn't. At least that's now known.
As I was using Microsoft Office 2016 I notice a number of American spellings in the menus. First I thought perhaps I hadn't set up something correctly. Reading further indicates the Microsoft Office user interface takes the language from the OSX operating system. I then checked the Language & Region setting. It was set to English so I thought that was the problem. I could see for example in Desktop & Screen Saver the spelling "Solid colors". I then decided to add English (Australia) and remove any other language so as to be very specific. That didn't help.
Unfortunately at this stage I don't seem to be able to find a way to remove the American spelling from the user interface for the Apple MacBook Air and thus Microsoft Office. I'm starting to get a feeling this may end up being one of those, they simply don't care enough about the Australian market. Happy for us to buy their products, but not enough to put in the extra yards to make it specific to the market. I hope I'm wrong.
Perhaps I'm wrong and there's something I'm overlooking. When time permits I'll drop into the local Apple Genius bar and see what they say.
Personally I don't think this good enough for either Apple or Microsoft. In the past I've tried to escalate language issues within Microsoft for years to no avail, so I don't really feel like expending that type of energy again for Apple.
It really irks me to think of the millions of Australians using Apple products who are constantly being shown American spelling. It's hard enough to spell correctly without being shown the incorrect spelling for words making us doubt ourselves.
Microsoft Office 2016 is available now for Office 365 users. From what I've read, for those who wish to purchase Microsoft Office product rather than subscribe, the release date is most likely around the Spring/September timeframe.
For those who have purchased my dictionary files, the files will continue to work as they did for Office 2013 and Mac OSX.
The preferred Australian English spelling for Microsoft Office.