Thanks to a tip from Miquel Hudin, I noticed that Apple has already made it possible for publishers to add books to iBookstore in Latin America: specifically, Argentina, Bolivia, Brazil, Chile, Colombia, Costa Rica, Dominican Republic, Ecuador, El Salvador, Guatemala, Honduras, Mexico, Nicaragua, Panama, Paraguay, Peru, and Venezuela. And it has also opened the iBookstore in New Zealand.
Simply go to iTunes Connect, Manage your books, and then choose Add Territories in the upper-left part of the window.
I assume that there will be a new version of iTunes Publisher today as well.
Note that I added a few of my books this morning, but they still say "Not on iBookstore" in the new countries. I suspect that will change during the day.
There are books in Spanish for sale already on some of the new iBookstores. To see a different country's iBookstore, in iTunes, choose iTunes Store, and then go to the very bottom of the window and click the flag in the bottom-right corner.
Then choose the desired country from the list. Note that not all of the listed countries have the iBookstore (some only have the App store).
Here's a screenshot I took after switching to the Argentina iBookstore. Actual books for sale, in Spanish. Note the currency, however, all in USD.
As of 9:23, my books are still not available in the new countries, even though one is in Spanish. I'll let you know.
It is interesting to note that "Libros" now appears as a category on Apple's LinkMaker page for the new Latin American Market (and Books for New Zealand):
This is very exciting and is definitely an auspicious start to this day of new announcements by Apple. Can't wait for the rest.