I agree that the would already should have had a lingua franca, but I must say that it English is far from the best candidate. The language is huge, and the grammar is full of irregularities. Pronunciation must be learnt case by case (why are "women" pronounced "wee-men"?).
It's also the only candidate. English is the most commonly learned foreign language by far[1], and I don't foresee any major economic movement to change that.
English has a momentum no other language have ever had. There is no language that has a larger body of knowledge online than English. Virtually all cross-border hobbyist communities, expert platforms, etc (eg Stack Overflow) are in English. People all over the world use English to communicate, even when nobody in the group has English as their native language. I was a member of a European student network called BEST, which had 0 member universities in English-speaking places and still the entire thing was in (bad) English. The entire EU is running on English informally, and I bet formally too a few decades from now (and not because we like the Irish so much). My startup has some customers in the UAE, in India and in Pakistan - their sites main (and sometimes only) language is English. The list goes on and on.
Chinese would've had a chance if they weren't so isolationist. Call me when the first Chinese language TV show gets popular outside China and Taiwan. I bet English language TV shows will be popular in China long before then (if they aren't already - I honestly don't know).
This is a common complaint, and one the purist in me is sympathetic to. These days, I have a more nuanced perspective on English.
Yes, English is huge and complex. However, the things we are trying to express are themselves huge and complex. A big language gives us many many colors to paint with. I mean different things when I say I am "sad", "down", "blue", "disconsolate", or "woebegone". There is a learning burden on English speakers to loading such a large language in their heads, of course. But, in return, we get a higher-bandwidth communication protocol.
The complaints about pronunciation are also common and valid in many cases. Things like the Great Vowel Shift lead to words that no longer sound like they are written for little useful reason. But in some cases, pronunication varies between similar-spelled words because their etymology is wildly different.
A word's spelling carries both pronunciation and meaning. When the pronunciation varies, it is often because the underlying morphemes are different even though they are spelled the same. This means the spelling doesn't teach you to pronounce it as well as you like, but once you can pronounce it, the pronunciation helps you know what it means.
And, as a lingua franca for the world, I think English is great. English is riddled with loanwords and is constantly assimilating terms from other languages that can't already be expressed well. In many senses, it's a global language because it is the set union of them.
"The problem with defending the purity of the English language is that English is about as pure as a cribhouse whore. We don't just borrow words; on occasion, English has pursued other languages down alleyways to beat them unconscious and rifle their pockets for new vocabulary."
English is THE candidate. Lingua franca is not decided by merits, but by adoption rate, which makes English is only choice on the table. It is the British empire+US hegemony, since WWII/Cold War that makes English lingua franca as it is today.
> It is the British empire+US hegemony, since WWII/Cold War that makes English lingua franca as it is today.
To be fair, it's also centuries of important contributions from English-speaking countries in science, technology, industry, aviation, literature, etc, etc, as well as, since WWII at least, music, TV, film and other forms of popular entertainment.
(also recall this cute poem: http://www.ling.upenn.edu/~beatrice/humor/english-lesson.htm... )