Open WALS or Glottolog or any other language catalog and you will see they categorize Chinese as a language family, consisting of multiple languages like Mandarin, Wu/Hui, Min, etc. You are free to disagree of course, but "Western linguists don't consider the dialects different languages" is simply not true to my knowledge.

> Western linguists don't consider the dialects different languages. If they do, they do it for political reasons.

Western linguists generally view the concept of a "language" as being a political one more than a linguistic one, and so rather than quibble about definitions they just use whichever word the people who speak the language/dialect would use. For example, from a book about Chinese dialects [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.

The Chinese language varieties are dialects because it is politically expedient for them to be so. The Western Romance languages are languages because it is politically expedient for them to be. Linguists shrug and move on to more interesting (to them) questions.

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

Serbo-Croatian is a special case. We all know that we speak the same language, but ‘the others’ are naming it wrongly.

Also, Slavic languages are very difficult for non-Slavs to learn, but very easy for other Slavs. And many are mutually intelligible.