The December weather is actually warm enough to sit on the beach, but most people who come to Dubai tend to just relax and do a lot of shopping at one of the enormous and modern malls here. The restaurant scene is very interesting as well, and you can eat cheaply if you follow the local workers, or go to one of the hotel restaurants and get world-class cuisine.
In Central America you could consider Belize. It’s small, but it’s got islands and beaches (not everywhere though) and forests and other cultural sights, and English is more or less the official language. It’s not as well organized as Costa Rica, but it’s not bad and it feels safe. The other to consider there is Panama, which obviously has a lot in common with Costa Rica. It has far fewer adventure activities and the good beaches are spaced out a bit, but still it’s a relatively rich country with tens of thousands of Americans and Canadians living there as well as visiting, so they have a good tourist infrastructure and it’s safe.
If you’re dreaming of a white Christmas, head to Tallinn to see the medieval city decked out in a blanket of snow, complete with flickering candles lining the streets and markets flogging quintessential Christmas curiosities and festive treats. And if that’s not enough seasonal charm for you, make for Rovaniemi in Finnish Lapland, the ‘official home’ of Santa Claus. Once you’ve dropped your gift list off with the big man himself, treat yourself to a husky sledding excursion or reindeer safari to explore the region in full effect.
Since flights to Mexico City from the US and Canada are usually quite cheap this time of year as well, this could be a perfect short cultural holiday. This city has great shopping, dining, and nightlife, and the central historic and tourist districts are far safer than most people would expect. There are ruins just out of town as well, so a bit of everything is available.