Twitter is at best a representative of people in the West. And only a small subset of those people.

Japan has a pretty large Twitter userbase, but this seems to only look at English words anyway.

I assumed new year would be something universal, because there was always a smaller spike right before it that I thought was christmas, so it wasn't big in the rest of the world.

The reasons why are complicated, but what we know so far is that the words "happy" and "new" and used excessively on this day, from which we conclude that people's moods are unusually positive.