There is only one English language and the definitive dictionary is the Oxford English dictionary.
It is currently 20 volumes in print form and is also available electronically. You can find full information here:
Oxford English Dictionary: The definitive record of the English language
There is a simplified and modified derivative of the English language, sometimes referred to as American English, which (I believe) uses Websters unabridged dictionary as the definitive reference. It has been suggested that it was simplified with fewer words and more phonetic spelling in order to help immigrants from non English speaking countries learn the language more rapidly.
Regrettably there is now an awful amount of slang used by both native speakers, for example, I was totally confused when hearing that a BT was in fact a shortening for Black Top, meaning a pavement, which when finally translated into English English, was actually a road!
However, there is still an atrocious amount of poor spelling, grammar and syntax error occurring which, to me, is unforgivable. One I find continuously irksome is the misspelling of amateur, i.e. amature, but then I'm a curmudgeonly, cynical old bar'd (sorry for the abbreviation)!