几天后用英语怎么说

In English, "几天后" is typically translated as "in a few days." The phrase "in a few days" comes from the preposition "in," which is used to indicate a point in time, and the phrase "a few," which is used to indicate a small, indefinite number.
Here are a few examples of "in a few days" in English sentences:
I will see you in a few days.
The project will be finished in a few days.
I will have more information for you in a few days.
In Chinese, these sentences would be translated as:
我几天后见你。
这个项目几天后完成。
我几天后会有更多信息告诉你。