Short short with English summary                         

5月5日は端午の節句で、3月3日は雛祭りだ。7月7日は七夕。1月1日は元旦。数字並べのゲームをしているようなのが日本古来の祭日である。その上、2・4・6・8、偶数月には数字並べの祭日はない。 こんな楽しみは、5月がメイで3月がマーチの欧米諸国では、あり得ないし、出来ない。その代わり、欧米では、一年後半四分の一、9月から12月までを、7の月、8の月、9の月・・・と二カ月ずらして呼ぶ言葉遊びをしている。クリスマスカードを書いていて、どうして12番目の月を10の月と言うのかなと考え込む欧米人はいない。

Do Japanese love numbers?
For Japanese, the 5th of May is a traditional important holiday, “Boy’s day”, with well-known “Carp streamer”. The 3rd of March is “Girl’s day” with cute sweet dolls. May is the 5th month of the year and March is the 3rd month of the year. 1/1, 3/3, 5/5, 7/7 and 9/9, all of these dates are traditionally important days. It is as if Japanese play a sort of number paring game. In addition, the numbers are only odds. No even numbered dates such as 2/2, 4/4, 6/6, 8/8 are holidays. For Europeans and Americans, they cannot enjoy this game, impossible for them since May is May and March is March. However, they play with naming of the months. I.e. September, October, November, are actually the 9th, the 10th, and the 11th month.
When one writes a Christmas card, no one ponders deeply why the 12th month of the year is December, the tenth month. You might think Japanese love numbers and good in calculation. The fact is that Japanese did not use the series of the numbers for naming the months. They did not use 1st month or 3rd month but “Mutsuki” and “Yayoi”. Even though 1/1, 3/3, 5/5 have been festive days. It is not at all so simple and easy to explain the background of these phenomena. Nevertheless, the 9/9 is a holiday as the date with doubled lucky number “9”. Perhaps if I had sufficient knowledge of Chinese or Korean culture there might be a simple explanation.
This topic about the dates and Japanese traditional holidays are internationally common. However, these days in Japan, the new name of the dynasty that begins on the 1st of May is much more important than the big fire and damage of Notre Dame of Paris. For the people in the world except Japanese, “Heisei” and “Reiwa” mean nothing, out of their interest. Practically useless. As to research modern world history or to compare statistics, the naming are not only inconvenient but also obstructive. So long, we Japanese have to fill the official documents with “Shouwa” or “Heisei” or “Reiwa”, the quality of our life and the BNP would fall.