我不太会说普通话

我普通话不太好。

You can just say 我不太会说普通话

there is that slight variation of 懂 and 明白. both mean understand but with 明白 it also means clear. in this case using 懂 is more suited to your need. but to clarify things, in terms of "know" do you mean listen? to speak? or to read and write, it would be better to specify in the sentence but for general understanding type, 我不太懂普通话 is fine

我不太懂普通话 和 我不太会说普通话 是相同的意思吗？各们母语者？ 一个广东人可以说“我不太会说普通话”，不代表他听不懂普通话。 一个人说我太懂普通话，意味着他可能听不懂，也不会说。