I checked Google & the archives & can’t find what I’m looking for so…
which countries traditionally allow for siestas?
I think pretty much any country allows siestas – that is, I don’t know any country where there is a law forbidding you from taking a nap in the afternoon. 
But if you mean where are seistas common, I think it generally would be those countries with very warm climates – those located somewhat near the equator. The ones I recall hearing about are southern Italy, Spain, Portugal, Egypt & much of the Middle East, Mexico & Central America, etc.
I recently had a professor from Taiwan. She says that over there, workers get an hour to an hour and a half for lunch, and most people take naps. No phone calls are taken, no appointments, etc., and many just put their heads on their desk and snooze till it’s time to begin work again. She says that they have found that the increased productivity after naptime makes up for the time they lose sleeping.
Sounds like a primo idea to me 
In Greece they stop working at 14:30 and come back at 17:00. It’s strictly forbidden to be noisy during that time, so that you won’t disturb anyone’s sleep.
Only exceptions are super markets and touristic areas. They change shifts at that times though.
It’s a hallowed tradition in China, too.
Alas, I’m afraid most employers would find the concept horrifying here. Oh well…
When we lived in Israel, there was hafsaka. Most of the stores would close for about 2 hours. I understand now that hafsaka is now pretty much gone.
Of course, when we lived there (in Jerusalem), we didn’t know how many people really observed this. The old man who lived in the apartment under ours came up and yelled at my wife for clacking across our floor in high heels during his rest time. Other people told us that we shouldn’t hang out our laundry during that time because the pulleys squeaked.
I can comment on Mexican siesta, but only for a very small part. I’ll start by saying I’ve never seen anyone sleeping on the sidewalk propped up against a building like in Speedy Gonzalez cartoons.
In Leon, Guanajuato, they have a “siesta” from roughly 2pm until 4pm. Time varies according to whom you work for, of course. And no one calls it “siesta” – it’s called dinner-time. Workers return to the their homes and have dinner with their families. The kids are generally back from school, and they have a good, old-fashioned family meal together. Of course my saying this is equivilent to saying that we United Statians all have good,- old-fashioned family meals together – people do their own things and it’s a generality. But it’s not a generality to say that they have (gasp!) four rush hours per day – the morning commute; the to- and from-siesta commute, and the evening commute (between 6ish and 8ish). Oh, yeah, because they have to two hour lunch, they work later into the night that we typically do. Most restaurants remain open, though, and it’s a toss-up for the shops. The more tradtional ones in the downtown plaza area will close.
This could be changing, though. For example I know what one particular GM plant there does: first, the hourly employees are bussed to work, from pretty much all over the state. This is a lengthy commute for a lot of the guys, and GM certainly doesn’t want to pay for twice as many trips. Instead, they get a 1/2 hour lunch, and the cafeteria food is an employee benefit for them (and it’s pretty good food). That, plus production schedules would be really quite chaotic during three-shift operations. I have to imagine that things are similar for VW, Nissan, and Ford, as well as all of the satellite suppliers they bring with them.
Mexico City is a mixture of the old and new. Commuting there is pretty much the same as commuting in metro areas here, i.e., it’s a pain in the neck but you get to a good job and get back to a good neighborhood, and that takes time. It’s mostly Americanized, i.e., no siesta. Of course by “mostly” I’m speaking of “first world” Mexico and not “third world Mexico.” This is third-hand information, though, as I’ve probably only personally spent 24 disjointed hours in Mexico City.
And finally, the word “siesta” in the parts of Mexico I do know refers to a nap, reguardless of the hour.