Re: why english?
Agreed with the reply.
And China has two main languages plus lots of others though Mandarin is maybe 90% of native speakers. There's a lack of available teachers in most countries outside western Europe.
Content: Wikipedia, for example, has 3 times more pages in English than any other language and I'm sure the WWWs page ratio is even greater.
In many countries, English is seen as cool (music, Hollywood, Facebook etc as article) and don't forget all those English phrases entering other languages (Le Weekend).
English is already a multinational language and unlike e.g. French, English's "standards body", the OED, is already global and welcomes foreign words into English (Lingua Franca?).
One might make a better case for Spanish - it is already a global language - but many of the same issues exist. However, why we (in UK) default to learning French in School is beyond me.
All those nasty American spellings and sports phrases seem a small price to pay for being a native speaker of the World language.