In the contemporary world, the Americans lead and the English follow, so if you wish to learn a useful language, the American standard of English is the one to learn.

During Soviet times, the standard taught was primarily that of the so-called "United Kingdom" (i.e. England). Recent textbooks, however, teach the American standard, apart from a few quirks of UK usage which haven't been noticed and edited out yet.

Trying to use a compromise language will only make you sound like Austin Powers, and just like Austin Powers, you will be laughed at.

That being said, most English speakers around the world are very tolerant of differences in pronunciation and accent, somewhat less tolerant of grammatical errors and rather intolerant of the irritating localisms of vocabulary that untraveled English people tend to use. The international standard that Anatolij writes about is the American standard of English spoken with various accents, any of which is acceptable, provided that the grammar and usage are basically American.