> A Chinese character is more or less equivalent to a word in English/French.
Most Chinese characters are monosyllabic, and most Chinese words are polysyllabic consisting of multiple characters. A Chinese character is a morpheme, and it also happens that many common words are also single character morphemes.
> Someone who speaks only Cantonese can read and understand text written by Mandarin speakers without any issue.
Because we've all been taught to read and write in Mandarin from the very beginning of our education. Again, Hong Kong is a diglossic society.
> They use largely the same grammar and vocabulary. Because Cantonese is ancient Chinese, over the years they have lost track of what semantic characters to use for some of the Cantonese words.
They share a lot of grammar and vocabulary (...but not all of it) because they share a language ancestor. Cantonese is not ancient Chinese, but it's a descendant that conserved a lot more consonants than Mandarin (and a lot of sound merger is actually happening right now in Hong Kong over the last 100 years, but it's commonly derided as "lazy sound").
> Once the mapping is done, you will be able to write down Cantonese and have it understood all over China. Since the work hasn't been done, you can only write down Cantonese with the help of some phonetic characters, which denote only pronunciation but not meaning. It's not gibberish, but neither is it proper written Cantonese.
See [https://books.google.ca/books?id=pFnP_FXf-lAC&pg=PA51] for a description of common strategies for writing Cantonese. Phonetic borrowing is one strategy, and the most common one, yes, but that's no different than characters in standard Chinese, the vast majority of which are a radical with a semantic category (but not a complete meaning) + a phonetic component.
A Mandarin-only speaker can decide for themselves how intelligible that colloquial Cantonese exchange on page 52 is, what with the difference in vocabulary and grammar.
Most Chinese characters are monosyllabic, and most Chinese words are polysyllabic consisting of multiple characters. A Chinese character is a morpheme, and it also happens that many common words are also single character morphemes.
> Someone who speaks only Cantonese can read and understand text written by Mandarin speakers without any issue.
Because we've all been taught to read and write in Mandarin from the very beginning of our education. Again, Hong Kong is a diglossic society.
> They use largely the same grammar and vocabulary. Because Cantonese is ancient Chinese, over the years they have lost track of what semantic characters to use for some of the Cantonese words.
They share a lot of grammar and vocabulary (...but not all of it) because they share a language ancestor. Cantonese is not ancient Chinese, but it's a descendant that conserved a lot more consonants than Mandarin (and a lot of sound merger is actually happening right now in Hong Kong over the last 100 years, but it's commonly derided as "lazy sound").
> Once the mapping is done, you will be able to write down Cantonese and have it understood all over China. Since the work hasn't been done, you can only write down Cantonese with the help of some phonetic characters, which denote only pronunciation but not meaning. It's not gibberish, but neither is it proper written Cantonese.
See [https://books.google.ca/books?id=pFnP_FXf-lAC&pg=PA51] for a description of common strategies for writing Cantonese. Phonetic borrowing is one strategy, and the most common one, yes, but that's no different than characters in standard Chinese, the vast majority of which are a radical with a semantic category (but not a complete meaning) + a phonetic component.
A Mandarin-only speaker can decide for themselves how intelligible that colloquial Cantonese exchange on page 52 is, what with the difference in vocabulary and grammar.