> If you compare the differences between English as spoken in Australia, England, and (even) America to the various dialects spoken in China, you can see how little descriptive value there is in referring to minor English variants as dialects or even independent languages.

Well, many linguists consider the different "dialects" of Chinese to be distinct languages, since in their spoken forms they are not mutually intelligible. What makes it more complex is that (a) their written forms can be mutually intelligible even when their spoken forms are not – in this regard the Chinese languages are quite unlike those of Europe or other parts of Asia, where spoken and written mutual intelligibility align much more closely; (b) the Chinese government, for political reasons, wants to promote the viewpoint of "multiple dialects of one language" over the (arguably linguistically more accurate) viewpoint of "a family of distinct but related languages sharing a common writing system", since it fears the later idea may eventually result in the breakup of China into multiple countries along linguistic lines, and thus that viewpoint is seen as a threat to Beijing's rule.

> Ultimately, the decision to declare a cluster of variations a dialect or separate language, or even admit it exits is a political choice, closely tied to national identity

It is true that sometimes questions about what is a language and what is a dialect can be deeply political. Whether Mandarin and Cantonese are separate dialects of one Chinese language, or two distinct languages within the Chinese language family, is a highly political question. Similarly, whether Macedonian and Bulgarian are two different languages, or two different dialects of one language, is a very political question (Bulgarian nationalists say Macedonian is a dialect of Bulgarian, Macedonian nationalists say it is a separate language). The same is true of the relationship between Hindi and Urdu, Serbian and Croatian, Romanian and Moldovan.

But that isn't always true. The question of whether Australian English and New Zealand English are two different dialects or one single dialect is not a subject of passionate political dispute in the way that (e.g) the difference between Bulgarian and Macedonian is. Neither the Australian nor New Zealand government cares much about the question – by contrast, the Chinese government has strong views about the language-vs-dialect question for Chinese.

> For instance, there is technically a New Zealand English, but it's essentially identical to Australian English aside from some minor differences in pronunciation.

It isn't just differences in pronunciation, there are also differences in vocabulary. For example, a portable ice cooler is called an esky by Australians but a chilly bin by New Zealanders. There are occasional spelling differences – Australians (like most other English dialects) usually write fjord, but New Zealanders more commonly write fiord. Another big difference is the widespread use of Māori words and phrases in New Zealand English, even by non-Māori New Zealanders (kia ora, pākehā, whānau, etc). There is even, in a sense, a difference in the alphabet – writing Māori loanwords with macrons (ā, ē, ī, ō, ū – used in Māori to mark long vowels and distinguish them from short ones) is common and accepted in New Zealand English, and in some contexts (such as government documents) is even preferred, whereas doing so in Australian English is rare.

Given all these differences in pronunciation, vocabulary, and occasionally even spelling, most professional linguists consider Australian English and New Zealand English to be two distinct (albeit closely related) dialects. I don't see any evidence that viewpoint is influenced by any political bias. Linguistics can at times be a politically fraught subject, but this particular linguistic question is not a significant political issue in either country.

> So, I don't see why people should really care if they see the Australian flag appears in the language menu.

I have never seen an Australian flag in a language menu. I have seen the US flag, UK flag, even occasionally some hybrid flag which merges the two (like [0]). Nobody creates multiple versions of a website in different dialects of English.

One does sometimes see country flags used to represent different national versions of a website, which will differ in more than just language/dialect, but also stuff like pricing, product range availability, marketing campaigns, etc. I don't think anybody ever objects to that. In this case, the flag is used to represent the country, not the language or dialect, and few object to using flags as representations of countries.

[0] https://commons.wikimedia.org/wiki/File:English_language.svg