Costa Rica is kind of the Thailand of Latin America in that they have great tourist infrastructure and it’s the easiest place to get around. They also have a lot to offer with the beaches on both coasts and many natural sights and activities, plus of course the Arenal volcano, which is a really nice area. San Jose is best as a place to just pass through on your way somewhere else.
Thank you. I think Kauai, Cancun, and Costa Rica could all be good choices for you. You’ll be looking at the last month (more or less) of the rainy season in each of them, but in the Tropics that usually means at most a few quick thunderstorms per week that typically last only 30 minutes or so. Kauai would be the most expensive of the three, although the most beautiful as well, and the easiest to visit since Spanish isn’t necessary at all.
The final month of the year marks the time when people in northern climates start looking around for an escape to the sun. Fortunately, there are big parts of the world that have their best weather of the year at this time, and are very cheap as well, once you get there. The best places to visit in December are of course close to the equator or even below it.
Southeast Asia is easier to deal with, and there are cheap flights connecting in the Middle East and landing in Bangkok, Kuala Lumpur, and Singapore. Each of those is a very interesting city, and there are many smaller places to go in the same region. In Malaysia there is Penang and Melaka. In Thailand there is Chiang Mai and quite a few others in that area. In Laos you can visit Luang Prabang, which sounds like it could be a winner for you. And there is also Siem Reap, which is home to the amazing Angkor Wat temple complex.