When it comes to可以代替Regarding嗎

In regard to, with regard to, regarding 和 as regards 都是同義的介詞片語，意為「至於、關於」：
例1. He knew nothing regarding(關於) [as regards, in regard to, with regard to] the case.
例2. As regards(至於) his performance, I am not in a position to make any comment.


"When it comes to"，最貼切的中文翻譯是”一講到”
例：　When it comes to parenting（一講到教子女）, I don't think you are an expert.

兩者雖然在用法上有近似之處，但明顯不能互相替代。

2010-01-15 19:43:48 補充：
如果是例2. As regards(至於) his performance, I am not in a position to make any comment.

改成When it comes to his performance, I am not in a position to make any comment.

兩句也可以表達類似意思．


但例一則不可以用When it comes to

說可以代替的話，極其量只是代替一半．

not applicable to all of them. they all have slighly different usage:
regarding ~ in relation to
with regard to, in regard to ~ concerning

the usage really depends on your sentence, hope this helps