I want to know which\what language she speaks. 用哪个对,why

I want to know which\what language she speaks. 用哪个对,why
I want to know which\what language she speaks. 用哪个对,why

I want to know which\what language she speaks. 用哪个对,why
在知道有哪几种语言的情况下（如：上下文中有提到,或者后面跟着几种选择）,选择which；如果不知道选项的情况下,就选择what,本句就是这种情况.

用which正确。
因为我想知道的是她说哪一门语言，which中表示抉择，而what问的是什么。

I want to know which is (the) best way to learn a language. I difficult as we expected. Think of what (a) small child does every