how do you say '' that's good , a good idea '' in chinese(mandarin)?
that's good =......................
a good idea =......................

Question

how do you say '' that's good , a good idea  '' in chinese(mandarin)? 
that's good   =......................
a good idea  =......................

Answer

英語是 主詞必要 的語言
漢語是 主題強調 的語言
漢譯 It's a good idea.時
it  僅是個虛主詞
idea 才是核心 才是主題
good 是描述這個核心的性質
主意不錯！ 點子很好！ 
庶幾近於漢語
Joseph所言 直中鵠的

Answer

真好主意啊。。。 呵呵

Answer

that's good =太棒了！
a good idea =真是个好主意！

Answer

好主意

Answer

不错! or 很好! It's good. 
这个主意不错！It's a good idea. 

I think 不错 is actually much better than 'not bad' in English. It's about how we use the language, other than just the literal translation.