Somehow other languages manage.

There's also quite some benefit for a org with official capacity to declare, against the wishes of some individuals, that say "santorum", "bromance" or "trumpgret" are not in fact English words.

Genuinely curious: how do other languages manage? Surely societies adopt words, idioms, shorthand phrases that haven't (yet) been officially sanctioned? There's plenty professional jargon that, while not "proper" English, is understood within certain contexts. There are also, to my old ears' chagrin, plenty of teenage neologisms that come into common usage, either through popularity or attrition.

Do other languages remain static? What happens when actually new things happen? Does "CD-ROM" just get integrated in whole? Translated? Rejected?

While I find many "new" english words unacceptable for my use, I wouldn't personally declare them "not English words". Moreover, if there were an authority over authentic english (especially American english) word existence and usage, I get the feeling that most would laugh said authority out of the room.

If the words/grammar stick well enough, the governing bodies let them in.

Until then, use them in an essay at school and you'll lose marks.

Some languages, like Afrikaans, won't loan words, and make their own up.

Where in Dutch we use computer, computernetwerk or lift, in Afrikaans it is rekenaar, rekenaarstelsel and hijsbakkie.

And in many languages, most famous in Dutch and German, one can make up words by putting other words together. Those aren't official untill some officials put it in some list. But that way, we can have koekiewet or Wutbürgerin or Nachtshoppen.

What happens when the US and UK disagree? Not to mention the other ~80 countries that use it). They can’t even agree on spelling.

For German there is an international body. Regional language differences are officially acknowledged. For example, Swiss High German has no Esszet and in Austria January is spelled "Jenner" instead of "Januar".

Eszett, Jänner

Keeping up with words is the job of dictionaries (pretty sure those exist for English), not of language regulation. For German language regulation means stuff like you're allowed to write Foto instead of Photo, but always Physik and never Fysik, or if you combine words like Schiff and Fahrt into Schifffahrt should it be written with two or three f, rules on when to use ß instead of ss and so on.