If any English that you hear, see, or read is instantly and perfectly translated to your native language, and vice versa, then all languages get equal footing. (Except perhaps for some primitive languages.)
There are other factors - English speakers readily adopt words from other languages as needed. This makes it a lot easier to expand. Compare with the Académie française: http://en.wikipedia.org/wiki/Acad%C3%A9mie_fran%C3%A7aise
Look at what people all over the world are constantly bombarded with - Hollywood's output is shown (and popular) everywhere. As are words like Coca-Cola, McDonalds, Nike and Apple. Even Bollywood is including increasing amounts of English in its output. Popular entertainers in various countries have also taken to singing some or all of their songs in English.
Look at generating input. There is a bias to a reasonably small number of symbols. A 500 key keyboard isn't practical (although variations exist). Having many modes and switching amongst them isn't that pleasant either. We already see people dropping case from English where is it mostly cosmetic. (Of course voice recognition is always around the corner but isn't practical in many environments and has always been around the corner.)
It is acceptable to speak English "badly" - did I tell you about the time that: the mat cat sat upon? I've heard from speakers of other languages that just getting the gender wrong in a sentence is enough to make it extremely hard to understand.
My prediction is that the number of speakers of English as a second language will continue to climb since it is the most friction free way of communicating in many circumstances, and that will rapidly lead to their kids adopting it as a first language. Heck all the people I know who have a non-English language as their first language have their kids speaking English as their first language.
TLDR: English makes a very good lowest common denominator
Esperanto is an attempt at a equal international language for all. http://en.wikipedia.org/wiki/Esperanto
Because English and English speakers are happy to adapt and change, the simplification is happening. Look at text messaging where superfluous extra words and letters get dropped, as does case. Even Hollywood is careful to keep language simple in their popular movies aimed at a worldwide audience.
An alternative, phonemic alphabet for foreigners might have more hope, though even then the use case is narrow.
I'm not getting it. What was the bad English speaker trying to say?
Although I'd say human to human and human to computer communication are very different, I'd agree with you that some languages are objectively better. There are ancient tribes that don't have words for numbers above two. Esperanto seems to be one of the easier languages to learn, at least for those already fluent in european languages. But when it comes to adoption, culture and ubiquity seem to be the most important factors.
Well, not only that. English usage will also drop because of long term economic and cultural effects. English had commerce, hollywood and popular music going for it.
But billions of people in emerging middle classes now, e.g in China and India, get their own "hollywoods" and music on, and they also get at least equal footing in the world trade-ways (commerce).
With a large cultural industry and commercial opportunities, they'll be just like Americans that could not care less about non-english speaking content (movies, books, series, webpages, songs, etc).
And the way they do that is by including English. For example see the second paragraph of http://en.wikipedia.org/wiki/Bollywood or consider the recent Korean pop success "Gangnam Style".
The english are a byproduct of the American cultural dominance in the pop field that is slowly corroded.