How to translate :在每个人的一生中,经验的积累是一个必不可少的过程.

在每个人的一生中,经验的积累是一个必不可少的过程.
The accumulation of experience is absolutely necessarily for each one's life.

the accumulation of experience is an essential process throughout one's whole life.

在每个人的一生中,经验的积累是一个必不可少的过程
Experience gather is indispensable as you go along (in your life)

In everyone'life,it is a necessary process to accumulate experience.

在每个人的一生中,经验的积累是一个必不可少的过程.
Experience accumulation is an essential process throughout one's whole life.

个人的一点意见:
It is an essencial process that one should accumulate experience throughout his whole life