I don't disagree that there can be fault lines of mutual intelligibility between dialects. I'm not even commenting on how we define dialects at all—all I'm saying is that the distinction between a dialect and a language is an arbitrary one that is made for political reasons more than linguistic ones, and that's something that even the sources for that Wikipedia page agree with me on. For example (emphasis added) [0]:

> The debate as to whether or not the varieties of speech used by the Chinese should be classified as separate languages or dialects of one language is a difficult one, with reasons on both sides. The main criterion according to which some scholars tend to use the English term 'language' for the varieties of Chinese, is the lack of mutual intelligibility between the various forms of speech, the fact that the "various 'Chinese dialects' are as diverse as the several Romance languages". On the other hand, since there are no extra-linguistic (political, historical, geographical, cultural) reasons to treat these dialects as individual languages, the tradition is to call them dialects of Chinese.

In the absence of nation states I suspect that we'd mostly talk about dialects and dialect continuums. Discrete languages are only really relevant as a concept because of the non-linguistic ties that bind a nation together.

[0] https://books.google.com/books?id=lCgnrA7Ke3QC&pg=PA1&source...