金笔的翻译是正确的。汉语里“自主”更像形容词而不像名词，而且词义太窄，使用不便，当初翻译为“自由”应该有语言使用习惯上的考虑。

Liberty: 1, the state of being free within society from oppressive restrictions imposed by authority on one's way of life, behavior, or political views.

             2. the power or scope to act as one pleases.

 

Freedom: 1. the power or right to act, speak, or think as one wants without hindrance or restraint.

 

语言中出现无法对译的情况很多，尤其是出自两种完全不同源的文化。你可以试试把“七经八脉”、“天地玄黄”翻译成英文看看。中日韩之间的翻译就很少会出现无法对译的情况。