I'd like to point out that Hekate apparently lives in Brazil, and is not an American who thinks the world revolves around the US (and yes, there are a lot of those here!).
Sure, American English is pretty universally understood due to movies and TV shows being shown throughout the world (and American phrases and slang are quickly picked up elsewhere), but that sure doesn't make it official in any capacity.
BTW, Canada uses a mixture of British and American English.
The US discussion is interesting. It is true that through popular culture many US origin words and phrases gain wide exposure in other English speaking places, and catch on there too. Australia knows and uses plenty of new US origin words.
However, even in the last 100 years, new slang from the UK also gains wide exposure through UK media, and is also then taken up in other places.
I am sure many Australians swear black and blue that things like 'cheers' (thanks), 'have a slash' (urinate), 'take the piss' (send up; take the mickey) are true blue authentic Australians terms. But I am old enough to remember when no one in Australia ever said them. They were, however, heard in UK television programs.
Like, the first ever series of 'Absolutely Fabulous' in 1992 features Patsy often saying 'have a slash'. It wasn't known or heard much in Australia then, but it certainly is now. I suspect that's due to it being in several UK films and TV programs.
Likewise the 1992 series of 'Absolutely Fabulous' featured Patsy saying 'cheers'. Her TV chat show appearance where she had stagefright and could only repeat in deadpan 'yeah, cheers, thanks a lot' through the entire appearance was much quoted in Australia at the time. (Pats ended the bit with a deadpan 'you can never have enough hats, gloves, or shoes' - which was also much repeated by Australian fans.) Before that 'cheers' (thanks) wasn't said much in Australia (I knew some 'cool kids' from Darlinghurst who ended their emails with it at that time though). I think AbFab and other films and TV programs of the day helped it catch on here.
Likewise 'take the piss' seems to have emerged in Australia only in the last thirty years. And that is from the UK, not the US.
The 'Aussie Aussie Aussie Oi Oi Oi' chant is derived from the similar, UK based chant, 'Oggie Oggie Oggie, Oi Oi Oi'.
I believe that people in the UK sometimes use terms like 'Uni' (University), 'no worries', 'walkabout' (the Royal family does them), these days. These are from Australia and may have been transported there through Australian made TV soaps.