Thanks for moving this discussion from GitHub to here. I can’t answer the first question, there are more knowledgeable contributors on here who might know more.
Generally the HOWTO does not necessarily reflect the case for specific languages apart from English, that’s true.
The 14 words for English is a measurement that results in the desired length of a clip. Of course that depends on speaking speed. In Cantonese that might be equivalent to 50 characters for example (I have no idea).
From a technical perspective, we could add a custom validator for Cantonese, which then can provide its own rules and when to reject a sentence when uploading. The code can be found here: sentence-collector/server/lib/validation at main · common-voice/sentence-collector · GitHub . As you can see there for English it tries to split in words, but individual language files do not need to use that. The rules for Thai for example count the characters and limit that: sentence-collector/server/lib/validation/languages/th.js at main · common-voice/sentence-collector · GitHub