Esperanto is a planned language and therefore should be included among the languages discussed in the book In the Land of Invented Languages. No doubt this is an admirable book, and it's one that I look forward to reading. However, I suspect that Ange Mlinko's knowledge of the history and development of Esperanto is sadly limited.
Mlinko suggests that: 1. "the most successful [planned language] may be the language invented by Marc Okrand and trademarked by Paramount Pictures (Klingon)."
2. "Okrent's book is a compilation of wonderful stories about batty inventors--some lovable, like Esperanto's Ludwik Zamenhof."
I would not venture to tell you how many people in this world speak Esperanto; nobody knows, exactly. However, in the recent 94th Congress of the World Esperanto Association in Bialystok, there were 1861 participants from more than sixty-one countries. This is just one of the Esperanto venues in today's world.
Nowadays it is so easy to get hold of information before writing an article. If Mlinko had, for example, consulted esperanto.info/, she would perhaps have reconsidered calling Ludoviko Zamenhof "batty"; neither he nor the countless millions who have used Esperanto since its introduction in 1887 have been more "batty" than average.