And some of them sound rather radically different from Mandarin. My wife speaks something called Hangzhou dialect (spoken just a few hours away from Shanghai) and when other Chinese hear it they sometimes think she is visiting from another country. On one occasion some people thought she was speaking English (it sounds nothing like English).

An example of the differences... in Mandarin to say "It is." you would say "Shi de." but in Hangzhou dialect you would say something that sounds like "Zede ye." The adverb "very" is "hen" in Mandarin but sounds like "molaolao" (though colloquially people often just say "mo") in Hangzhou dialect.

The differences between the various dialects are fascinating sometimes radical and they must have developed for many centuries in near isolation from one another to get where they are today.

I'm no expert, but I always wondered if it was a result of the language being tonal. In England, you have dialects that can sound so different that it could be another language to the untrained ear. However as English isn't tonal, there's a larger margin for error (so to speak) - accents can exist without transforming the word. Whereas with a tonal language, an accent could change the language more dramatically.

Though what's also interesting is some of the different languages and dialects in China also have different sentence structures (eg verb placements).

>However as English isn't tonal, there's a larger margin for error

True. The tones are critical in a way that can be very difficult for non-native speakers to grasp. Here are the four tones used with the words mā (mother), má (hemp), mǎ (horse) and mà (to curse) with an extra for ma indicating a question http://www.youtube.com/watch?v=QRkCf6Djprs.

And in that video she pronounces them far clearer than would be used in actual conversation.

The multisyllabic nature of English and relatively complex sentence structure probably aids comprehension with different accents too.

The history of the language is quite an interesting one, in my opinion: http://en.wikipedia.org/wiki/Historical_Chinese_phonology