This is a very big topic and an interesting one! On a personal level I love the richness and diversity of English usage. In France we have the Académie Française, which is mostly perceived as a bunch of old farts in a dusty cupboard completely out of touch with reality...but they are the official guarantors of the French language.
I would not advocate for any such body in the English-speaking world (heaven help us if we tried!
) but, that said, the practicalities of working in a language where so much varies from one country and continent to another can lead to a lot of head-banging. I have clients who insist on American or British English, and as a copywriter, the key thing is consistency. But the lines are blurring. For example, spell check in Word no longer flags z-words like 'publicize' as a mistake even if GB English is the default language. On a different level, working with many non-native English speakers in France and Switzerland, you can end up with imprecise use of terms (often originating in false friends from other languages). So some sort of standard reference for English is essential. BTW, I have no idea how the translators and interpreters at the UN or EU keep their sanity.