不屈不朽既英文係咩？

應該係 "不屈不撓", 唔係"朽.
英文可以用: Indefatigable.

係一個 adjective, 意思係,不屈不撓, 永不言休之類.

e.g. An indefatigable swimmer! 一個不屈不撓的泳手!

I think you can say "unfailing" or "never gives up". Actually, it depends on the context of the sentence and passage.

You can put it this way.... Someone never gives up.
You may also say... He has an unfailing faith.

Hope this helps.