One of the world’s more interesting examples of a market failure is the general inability of Esperanto to secure its intended role as a universal second language. If a great many people spoke Esperanto, it would be reasonably worthwhile to devote one’s time to learning it. Knowing that there was even a 30% chance that a random person encountered in Estonia or Italy or Japan would speak it, the energetic traveller or businessperson would have a pretty good incentive to learn at least a bit. If few people do, conversely, it is not worth anyone’s time. This is what economists call a network effect: having a fax machine when nobody else does is not very useful. Likewise, having a telephone or internet connection. The more people subscribe to any such network, the more valuable the network becomes to everyone. Such networks tend to explode in usage once they cross a critical threshold of popularity. Since the development of a base of speakers generally depends on such individual choices, it remains perpetually stuck at a low level of usage.
The idea of an invented universal second language is appealing for many reasons. While English has certainly emerged as a world language, it is not without significant cultural baggage. The forces that spread English - from the British empire to American ascendancy and the dominance of English cultural and technological materials - are inevitably connected with structures of dominance and submission in the world. While Esperanto does borrow from other languages, it seems sensible to say that it is free of at least a good portion of this kind of baggage.
Another serious issue related to second languages is how quickly they shrivel when not used. Much as many Canadians who learned the language as children would like to avoid forgetting French, it is very hard to maintain in the absence of a need to use it. When in an environment where one is virtually never exposed to the language, such as on Canada's west coast, one's knowledge fades quickly indeed. If everyone spoke one common language, it is quite likely that each person would be exposed to it often enough to gain and maintain facility in its use.
The message is simple, then: rest of the world, please learn Esperanto. Once two billion or so of you have, I will set upon the task myself.
This node has been modified from a post on my blog, at: http://www.sindark.com/2006/09/03/on-esperanto/