Nietzsche said truth was based off of the thoughts of the majority; if everyone thought the earth was flat then the earth was flat. So, Nietzsche is suggesting that truth is subjective and not based off of any universal truths. Truth, based off of this, can be changed. It is based off of biases, cultural difference and language. Since language can mean different things to different people, and can be construed differently, the same words can mean different things to different people. Therefore, truth is generated by the most excepted concept.
So, if the entire world believes something absolutely crazy, it will be accepted as truth.
Like, for instance, that the earth is flat: