为什么是Merry Christmas?
Google 这么说：
"Merry Christmas and a Happy New Year" (thus incorporating two greetings) was in an informal letter written by an English admiral in 1699. The same phrase is contained in the 16th century secular English carol "We Wish You a Merry Christmas," and the first commercial Christmas card, produced in England in 1843."
1699年一位英国上将在一封非正式的信里写到“Merry Christmas and a Happy New Year”. 16世纪的英国圣诞歌里也包含了同样的说法“We Wish You a Merry Christmas”。而1843年英格兰的第一封市售的圣诞卡片上，也印有相同的祝福。
蛋词君这么说：
"Happy" is an emotional condition, while "merry" is a behavior. "Happy"感觉像一种情绪，而"Merry"感觉是一种行为，会要做什么事情来庆祝。
比如，英语中有一种说法：
The more, the merrier 越多，越快乐
但是在英国，可能会说Happy Christmas
British people say "Happy Christmas"
北美主流还是Merry Christmas
Wish you a very merry Christmas