Ludwig Zamenhoff invented the simple international language in 1887. The Economist sees doom for the language that has never really taken off.
It remains thin on the ground… partly because language, more than any other tool, benefits from network effects. The more people who speak a language, the more desirable that language will be. This is of course why Esperanto speakers play up the biggest possible numbers for their community—the hopes that others will join, for the benefit of being able to use Esperanto with more people.