Interestingly, while English was spoken by about 10 % of the world's population in 1900, and by about 11 % in 1950, it is today spoken by about 8.5-9 %. The corollary is that, for better than 90 % of the world's population, it is not the de facto means of international communication.
David Wolff:
English is a very difficult language to learn unless you've been immersed in it since birth. English spelling is said to be more difficult than any other language except Gaelic. English grammar, although it may be fairly simple, is riddled with exceptions. Verbs are very often irregular. Many people just aren't going to devote several years of effort to learn it!
English has gained its present stature because of the current economic and political power of English-speaking countries. In the past, every super-power has briefly seen its native tongue used internationally: France, Spain, Portugal, the Roman empire. In fact, one of the main reasons why Esperanto was never adopted by the League of Nations was that France blocked efforts to adopt it. At the time, French was "the international language", and France expected it to stay that way forever. They
were proven wrong within twenty years.
Konrad Hinsen:
Although many people all over the world study English and often think they speak it well, the number of people who can participate in a non-trivial conversation in English is very small outside English-speaking countries. Knowing English may be sufficient to survive as a tourist in many places, but not for more.
Sylvan Zaft:
One Chinese Esperanto speaker described Esperanto as a linguistic handshake. When two people shake hands they both reach out halfway. When two people speak Esperanto they have both made the effort to learn a relatively easy, neutral language instead of one person making the huge effort to learn the other person's difficult national language and the other person making no effort at all except to correct his/her interlocutor's errors.
