I second all of the Central/South America suggestions. Flights to Central America, in particular, are relatively cheap and fast, and there's little to no jet lag. That will help you not waste your vacation time flying or being jet lagged. (Asia is great, but it's a bit far for a week.) Very nice hotel rooms can be had for $50 (or adequate ones for much less), and meals are equally cheap.
It's always nice to know the language where you're going, but in this case it's not 100% necessary. I've been working on teaching myself Spanish, but I knew nothing when I first went to that part of the world, and I was fine. Smiles and gestures can get you a long way, and a lot of people know some English. Even if you just learn a few words, people will appreciate your effort.
If you'd like to stick to an English-speaking place, try Belize or Roatan. Everyone speaks English in Belize. Roatan is an island off the coast of Honduras that was originally primarily English-speaking, having been settled by former African slaves (and pirates!, whose white descendants are still there -- ran into some at a restaurant and it was the most surreal thing), but now has more mainland Honduras (and therefore Spanish-speaking) influence. But still lots of English there. Roatan has, as you might expect, mostly beach-related activities. Stay in West End (local, cheap), not West Bay (touristy, expensive), but take a taxi (or hitchhike) over the West Bay to swim in their beautiful beaches and feed scraps to the reef fish. Drink Monkey La-Las. In Belize, I've done a surf-and-turf week twice, and I loved it both times. A few days on Caye Caulker (small island with no cars, mon) and a few days in San Ignacio (jumping-off point for hiking, spelunking, river tubing, etc.). On Caye Caulker, do a snorkeling trip to Hol Chan Marine Reserve and Shark/Ray Alley with Raggamuffin Tours. And go to the bar at the Split (where the island literally split in half years ago) and the I & I Bar -- even if you don't drink, it's just a fun place to people-watch.
Guatemala is often overlooked (even my fiance turned up his nose at it), but it is gorgeous and dirt cheap. Lake Atitlan is beautiful. Pick a place on the lake to stay, and then spend each day catching a little local boat to other towns to explore. Or borrow a kayak from wherever you're staying. Or go hiking in the hills around the lake.
I've only been to SE Costa Rica, but I really liked Puerto Viejo. You can rent a bike for about $5 and go along the black sand beach.
Ecuador is awesome, and I'd love to see more of it. The Hilton Colon in Quito is about $50/night but is very nice, and just a few blocks behind it is a huge market where you can get all things alpaca, some good food, etc. All very cheap. Great Christmas gifts that look luxurious and exotic but cost you $11. (Edited to add: The Galapagos islands really ARE all they're cracked up to be. Amazing photos and experiences I'll never have anywhere else. I did a trip with G Adventures in my more spendypants days, and a couple on my trip said they had just gotten themselves over to the Galapagos and then hopped on our trip at the last minute at a huge discount. Maybe have a Plan B if you're going to do that, but it might be worth a try!)
I liked Panama but just did sort of a quick group tour, with multiple stops, so I'm not really sure what to recommend. Panama City is a nice city, but it comes with a higher price tag than most of Central America.
As you might have gathered, I love that part of the world, so please don't hesitate to ask if you have any other questions! Got any room in your suitcase for me? :-)
