千秋万代的英文：
[Literal Meaning]
thousand/autumn, year/ten thousand/generation
tens of thousands of years

[解释]
一千年，一万代。指世世代代，时间很长。

[Explanation]
a very long time

[例子]
科学家们想找到一种人类千秋万代都使用不尽的能源。

[Example]
The scientists are looking for a type of energy that can be used for a very long time.

[英文等价词]
throughout the ages; for all generations to come

May our country be prosperous throughout the ages.
愿我们的祖国千秋万代,永远昌盛。