These hands spoke of stubbornness of mankind, of the will to work not only as one's strength permits but beyond the limits of one's power.

【翻译】这双手诉说着人类的顽强，诉说着不仅在人类自我力量允许的，而且也超越自我力量局限的乐于工作的意志。

本句中的关键词语及分析：

1. speak of：谈及；叙说；描述

2. of the will to work：承前省略了spoke；spoke of the will to work，意为“诉说着乐于工作的意志”

3. as one's strength permits：时间状语从句，意为“在自我力量允许之时”。not only...but also... 连接两个并列成分，但是not only 连接的是“as 从句”，but also连接的是“介词短语” beyond the limits of one's power。