I think you're confusing a reasonably short period in recent history with "forever".
In History there were quite a lot of "international languages of trade" other than English. It seems to depend very much on which nations were the top empire of the age and because the last two top empires were English-speaking countries (first Britain, then after that the United States), the English language has been dominant as a second language for a over a century now, but before that the English language already existed in a form very similar to the modern form and yet it wasn't at all an "international language of trade" (in fact, at least in Europe, before English it was French that was the dominant language of trade).
I bet that the next "international language of trade" will be Chinese.