Correct/Polite way of asking "Can we speak in chinese?"
In eastern asian languages, hints are very important, thus, if you have already said "你会说汉语吗?", it has included an indication of "让我们说汉语吧" and the part you are asking for is actually an unnecessary part of the communication. You can just switch to your Chinese mode after that sentence as a notice.

It is the same case in English. When you say "Can we speak in Chinese?", obviously you are not inquiring if we really have the ability to say Chinese, rather, it is an indication including the sentence "Let's speak Chinese.", which you will not speak aloud.

But it is important you know the correct answer. “（咱们/我们）能用（普通话/汉语）说吗？”