This is their red letter day.

今天是他们大喜的日子。

youdao

Today is my red letter day, I am the happiest person in the world.

今天是我的大喜日子，我是全世界最幸福的人。

youdao

It was a red letter day for the family when Carmen came home from the war.

对这一家子来说，卡门打完仗回家的那一天，是个值得纪念的好日子。

youdao

To Pune, 29 February 1996 add Nairobi, 24 February 2003 as the red letter days of Kenyan cricket.

BBC: Nairobi fans savour historic win

Tomorrow is also a red letter day for another reason - explained here in another, somewhat less impassioned letter from Carwyn Jones, this time to the Deputy First Minister.

BBC: Preparing for the crunch ahead

That date is generally taken three years from the point at which policyholders received their red warning letter from their provider.

BBC: Endowment mortgages: Legacy of a scandal