Of course, 30 years ago when I was a grade-school kid reading Agatha Christie mysteries, I was completely at a loss with "fortnight".
One of the differences shows up in a few prepositions.
In/on the street, at/on the weekends.
The differnces are pretty minor.
The language isn't called the "English" language for no reason! The only correct version is the English used in ENGLAND. Therefore. As England is part of Britain. The only correct version is british English.
American English is often referred to as "stupidize" by TEFL tutors in Europe anyway. And many people in Europe that use American English in an English exam will certainly FAIL !
Also, please note that much of your post is insulting and goes against the terms and spirit of the forum. Here all variants of English are respected and regarded as equal. If you find that offensive, then please look for a British-English-Is-Best forum. Our approach is international to reflect the nature of the English language.