How different are Chinese dialects?

Question

How different are Chinese dialects, on average, relative to the differences between European languages?

Are the dialects spoken in Western and Eastern China as different as, say, Russian and Polish, or Italian and Spanish?

Answer 1

Your question is an interesting one, in general how to compare the comparisons of languages and more specifically about the Chinese family.

The usual qualitative measure of difference is mutual intelligibility; but quantitative measures of this are hard to come by except by a large collection of anecdotes or great linguistic experience. That is to say there is not enough electronic material in all these varieties to do a computer comparison.

Also, labels like Mandarin, Cantonese, etc, are complicated by politics, history, culture, and translation, and may force thresholds that are in reality vague or not even there.

Most of the details of your question are answered by the wikipedia page on the varieties of Chinese languages

For most of the following there are many details left out, so consider this a broad idea with lots of small exceptions.

There are seven primary dialects of Chinese: Mandarin, Wu (Shanghainese), Gan, Xiang, Min, Hakka, and Yue (Cantonese). These dialects are all mutually unintelligible.

Within each of these dialects, there is a continuum of intelligibility, but from the extremes may not be intelligible (the wiki page gives many examples of unintelligibility within a dialect).

To say the differences are as much as the differences within say Romance is difficult. But it is often repeated that the Chinese varieties are as far apart as the Romance languages. What I think that means is that if you know one of the Chinese varieties, learning any of the other varieties is just as easy as say a French person learning Italian.

Some notes about your question:

• The writing set is the same for the great majority of the Chinese Languages. There might be some very minimal moving around of characters to reflect syntax change and a some different choice of characters to show some change in vocabulary, but writing is mostly understandable by everyone, no matter what the writer actually thinks they're speaking. That is to say that, someone from Beijing can easily read a newspaper articles written by Cantonese speakers, much more easily than say a French person could understand a Romanian newspaper.
• the state language of PRC is Mandarin, so everybody in school learns it, even though the local business and home language is primarily something else. So non-native-Han speakers are usually bilingual.
• the greatest change over direction is from north and west to south-east, not east to west. The western part of PRC (Gansu, Qinghai, Xinjiang, Tibet) was colonized by Han Chinese and ethnic Han there speak Mandarin (the non-Han locals speak mostly Turkic or Tibetan). That is, someone from Chengdu and someone from Harbin can more easily understand each other, but neither could follow at all a Cantonese speaker from Hong Kong. The Cantonese speaker could probably understand both of them though because of Mandarin taught in school.

To summarize, Chinese languages are very loosely related like Romance, for example Mandarin and Cantonese are like Italian and French, and even within Mandarin/Italian there are large differences between varieties (like Hebei vs Sichuan and Tuscan (standard) vs Sicilian). Don't take the analogy too far!