Is it possible to create Cantonese user dictionaries? Is there a technical reason why user dictionaries behave differently than built-in ones (e.g. a faster read-only database?), and will this be changed in a future update?
Not possible at the moment, should be supported in 4.0.
User dictionaries use a totally different format from built-in databases and from flashcards, which is why they don't all get the same capabilities at the same time.