Because of this thread about English example sentences containing the word Esperanto, I landed on the Google Trends page for Esperanto. (found here) Google Trends is a tool for viewing statistics for the popularity of search terms on Google.

When I saw the graph, my thoughts were, in order:

[list=1]
What in heaven's name is that massive spike in December 2009?
Wait a second... why is the search interest for Esperanto declining? D:[/list]According to the annotations in the graph, the answer to my first question is that it was Esperanto's 150th birthday.

I haven't found a definitive an answer to the second question (I doubt I ever will), but I believe one of the keys to solving it is realizing that the data is most probably relative, not absolute.

I think the absolute amount of searches for Esperanto is likely still increasing, but the total amount of Google searches is increasing even more quickly. Probably because the internet has grown more and more mainstream and less nerdy over the past decade, meaning the kind of people that might be interested in learning a rare language as a hobby in the first place make up a smaller part of the users of Google. Also, people who want to communicate internationally would be more likely to be early adopters of the internet, meaning the Esperanto community probably made up a bigger part of the online world a decade ago than now.

At least, I hope.

Rajzino:What in heaven's name is that massive spike in December 2009?

Here is your answer:
http://www.huffingtonpost.com/2009/12/15/l-l-zamenhof-google-logo_n_392299.html

Alkanadi:Here is your answer:
http://www.huffingtonpost.com/2009/12/15/l-l-zamenhof-google-logo_n_392299.html

Oh, if it was celebrated on the front page of Google that makes even more sense than only that it was the 150th birthday. I thought it must have been various sites and other news outlets who dedicated a small piece on Esperanto, but that doesn't really explain the massiveness of the spike so well.

Funny thing with Fulda.

It's the city in Germany, which generated most interest in the searchphrase “esperanto” (12.5 times more than Buenos Aires, which is the second one on the list, and 25 times more than Warsaw, which is the sixth). “Fulda - City in Germany” is the second most popular on the list of similar subjects and searchphrases “fulda” and “fulda esperanto” are the two most popular similar ones.

It all looked quite suspicious until I saw few next searchphrases: “hotel esperanto” (the 3rd), “hotel esperanto fulda” (the 5th). There's a congress centre there called “Esperanto”, which is responsible for so much of the “esperanto” searches all over the web.

It makes number of searches for the language Esperanto even fewer, which is quite sad.