Okay, I'll resolve, and declare @Angst the winner.
This map is taken from:
https://en.wikipedia.org/wiki/Labour_Day
Red: Countries which celebrate labour day on May 1.
Green: Countries which celebrate labour day on a different day
Yellow: Another holiday is on May 1.
Some of the countries which were brought up:
Britan is yellow: Apparently Britain has a moving holiday which doesn't have any good reason on the first Monday of May, therefore no labour day.
Japan is green: After WW2, they made their own labour day, which is somehow fused with their own thanksgiving, due to unclear historical reasons
South Korea is gray: It's indeed no public holiday there. While I don't have any data to support this, I would guess that they didn't feel like having a left-wing holiday after losing to the communists
North Korea and Laos are red: I guess there's no doubt that this is correct?
Some other countries where I know:
Finland is yellow: They celebrate May Day on the 1st of May
The Netherlands is grey: They have the king's birthday on April 27, and liberation day on May 5, so that would be a bit cramped. Kinda ironic that they workers don't get their day off, because of the monarchy (okay, they get a day off, but you know what I mean). I actually looked up this map when I was living in NL, because I saw that a ton of other countries are celebrating labour day, and wondered if NL is an exception. Yes, it is.
So, I guess this was a tad bit toooo specific after all :/.
This map is taken from:
https://en.wikipedia.org/wiki/Labour_Day
Red: Countries which celebrate labour day on May 1.
Green: Countries which celebrate labour day on a different day
Yellow: Another holiday is on May 1.
Some of the countries which were brought up:
Britan is yellow: Apparently Britain has a moving holiday which doesn't have any good reason on the first Monday of May, therefore no labour day.
Japan is green: After WW2, they made their own labour day, which is somehow fused with their own thanksgiving, due to unclear historical reasons
South Korea is gray: It's indeed no public holiday there. While I don't have any data to support this, I would guess that they didn't feel like having a left-wing holiday after losing to the communists

North Korea and Laos are red: I guess there's no doubt that this is correct?
Some other countries where I know:
Finland is yellow: They celebrate May Day on the 1st of May
The Netherlands is grey: They have the king's birthday on April 27, and liberation day on May 5, so that would be a bit cramped. Kinda ironic that they workers don't get their day off, because of the monarchy (okay, they get a day off, but you know what I mean). I actually looked up this map when I was living in NL, because I saw that a ton of other countries are celebrating labour day, and wondered if NL is an exception. Yes, it is.
So, I guess this was a tad bit toooo specific after all :/.