用英语翻译：我根本听不懂你在说什么

I can't understand what you're talking.

一般来讲，美国人之间说“我听不懂你在说什么”，他们会这么说：

Speak English, Please.
或者：
English! English!

我觉得这种表达方式很有意思，提供给楼主作参考吧，虽然不一定用的上。
个人意见，仅供参考。

i dont know wtf r u talking about.. -.-

好吧是I completely cannot understand what you are saying

I can't understand what you say.

I have no idea what you are talking about.

I simply do not know how you listen to what that