[yorwba]

The situation is somewhat comparable to English and French, where a significant shared vocabulary with identical orthography allows making educated guesses. That's not enough for fluent understanding, since many words that are common in one language only appear as rare alternatives to more natural expressions in the other. For example, the Cantonese pronoun 佢 doesn't ever appear in Mandarin texts.

[barry-cotter]

Except the average educated Macanese or Hong Kong person can’t write in Cantonese. They write in something much closer to Standard Mandarin, with its grammar and vocabulary, than Cantonese.

It’s much more similar to the sistuation with Arabic where the various “dialects” are as distinct from each other as the Romance languages, i.e. French, Spanish, Italian etc. but the only written standard is Modern Standard Arabic. Mandarin or something close to it is at least someone’s native tongue. MSA is about as close to Maghrebi or Mashreqi Arabic as Latin is to Portuguese or Romanian.