"Christmas is the one time of year when people of all religions come together to worship Jesus Christ." ( Bart Simpson).
The Japanese don't celebrate Christmas. They will work tomorrow. Sucks to be them. Don't feel to bad though, they will make up for it January 1st.
This Saturnalia (officilally December 17th, but if the Romans stretched the celebrations, so can we) is even more special as Saturn and the moon are brighter than ususal thanks to their angle in the sky.
Indeed, most cultures plagued by short days in December go nuts with eating, drinking and gift giving. And they have since way before Jesus was born. Granted, they also go nuts when days are at their longest at the end of June. When you think about it, the lenght of days, even with electricity, is quite important.
So, lets all celebrate that days are getting longer. And by January 1st even the sceptics will agree they are. So eat, drink and be marry! And if you are in the Southern Hemisphere, enjoy the long days to.
And if religion helps with the celebrating, good for you.