請問有人知道「人日」(初七）的英文是什麼？

Human Day.
In Japan, Jinjitsu (人日, jinjitsu?), literally "Human Day", is one of the five seasonal festivals (五節句, gosekku?). It is celebrated on the 7th of January. It is also known as Nanakusa no sekku (七草の節句, nanakusa no sekku?), "the feast of seven herbs", from the custom of eating seven-herb kayu (七草粥, nanakusa-gayu?) to ensure good health for the coming year.
The name comes from an ancient Chinese custom, whereby each of the opening days of the first lunar month was assigned to a particular creature, which it was forbidden to kill on that day: thus the first seven days of the month were Chicken Day, Dog Day, Boar Day, Sheep Day, Cow Day, Horse Day, and Human Day: on this seventh day, no punishments were handed out to criminals.
The celebration of the feast in Japan was moved from the 7th day of the first lunar month to the 7th of January in the Meiji period, when Japan adopted the solar calendar.

Retrieved from "http://en.wikipedia.org/wiki/Jinjitsu"

This is 中國人春節既習俗... 係唔會有一個共識既英文詞組

If you wanna introduce this custom in English, then just simply say "A everyone's birthday" in stead

大 年 初 七 人 日 節
顧 名 思 義 ， 人 日 即 人 的 生 日 。 這 不 是 某 人 生 日 ， 而 是 全 人 類 生 辰 。 至 於 節 日 起 源 ， 根 據 《 占 書 》 記 載 ， 指 出 由 初 一 開 始 ， 上 天 創 造 萬 物 的 次 序 是 「 一 雞 二 狗 、 三 豬 四 羊 、 五 牛 六 馬 、 七 人 八 穀 」 。 所 以 初 七 便 是 人 日 。 在 人 日 ， 香 港 市 民 喜 歡 吃 及 第 粥 。 所 謂 及 第 ， 是 希 望 在 科 考 場 高 中 狀 元 。 人 吃 及 第 是 取 其 好 意 頭 的 意 思 。 (See: http://www.rainbowisland.com/rainbow/history/face/face.asp)

There is no formal English name for "初七" this date because it's a Chinese festival, not a western festival but we can call it the "Seventh day of the Lunar New Year since "初 一" is called Lunar New Year's Day (see http://www.labour.gov.hk/eng/faq/cap57f_whole.htm#q1)

For "人 日", I would say the Seventh day of the Lunar New Year is everyone's birthday" since western has no such concept.

According to wikipedia, the Chinese 人日 is known as the [Common Man's Birthday].