I
can't understand what you mean.或I can't understand what you said.或I can't understand your words.或 I didn't catch what you said.
I can‘t underestand what you said.
或者
I can’t underestand your words.
最简单的译法···I cannot understand what you said.···
I can‘t underestand what you are talking about.
I can underestand what are you talking about.