For December 15th, if you go to the Google home page in a number of countries and languages, you’ll be greeted by the Esperanto flag! Link to Google France.
December 15th is considered the anniversary of the publication of the language by Zamenhof, and is the closest thing to a ‘national’ holiday for Esperanto speakers.
Weirdly, if you go to Google Canada, you only get the flag if you select French. And if you go to Google Poland, you only get the flag if you select Polish. After looking around a bit more, it seems to be only non-English pages. And countries that have only English pages, such as Australia, don’t have the flag at all.
Google Israel too Interestingly, only the Hebrew version of it, though – neither the English version nor the Arabic one show the Esperanto Flag…
The date being celebrated, BTW, is the language’s inventor – Zamenhof’s – 150’s birthday (15/12/1859); nothing to do with any official date related to the language itself, AFAIK.
ETA – Eyebrows 0f Doom, I don’t see it on www.google.com.
Interestingly, only the Hebrew version of it, though – neither the English version nor the Arabic one show the Esperanto Flag…