> I suspect the only reason Chinese is categorized as a single language is ignorance and Eurocentrism.

Ignorance, perhaps, but not necessarily Eurocentrism. Viewing Chinese as a single language – often with Mandarin as a prestige "dialect" of it – is a common position of Han nationalists.

Attempts by some Western linguists to treat the Chinese varieties in a way that emphasizes their mutual unintelligibility and downplays the importance of the common writing system, have even been attacked by said Chinese nationalists as being "anti-China". It is very similar to how, decades ago, many Russians bristled at attempts by foreign scholars to view Ukrainian as a language in its own right, since their position was that Ukrainian and Belarusian are simply some aberrant or low-prestige forms of the Russian language.

I wasn't talking about Mandarin and Cantonese as "dialects", I was talking about different dialects of Mandarin as spoken in Beijing (which the official dialect is based on) versus e.g. Sichuan. Those are mutually intelligible similar to the varieties of English, but they are markedly different in details of their pronunciation, word choice, and occasionally grammar. European languages aren't the only ones with hard-to-understand regional dialects.

That makes sense, but I don't see why this is any more of a barrier to adopting Chinese than it is for any other language - like you said, European or Romance languages have difficult regional dialects, but somehow they're widely supported by Google Assistant.