Halve the red cabbage and shred it finely, each piece no wider than a pencil. Do the same with the Chinese cabbage then put both in a colander and rinse under cold running water.
Slice the radishes into quarters or thin slices, then mix with the cabbage and tip into a bowl. Scatter the salt over.
Place a plate on top of the cabbage, put a heavy weight on top, and set aside in a cool place for 4 hours.
In a small bowl, mix together the rice vinegar, fish sauce, chilli paste and chilli flakes into a soft, deep rust-coloured paste. Peel and finely cut the garlic into paper-thin slices and add to the paste.
Slice the spring onions, stirring them into the paste. Peel the ginger and shred each into fine matchsticks.
Rinse the cabbage in a colander, removing much of the salt. The cabbage will have relaxed. Transfer to a large bowl then tip in the chilli dressing and toss thoroughly to coat the leaves.
Pile into the clean storage jars, seal and set aside in the fridge for 4 days. I like to turn the jars upside down each day to encourage the dressing to trickle over the vegetables, keeping them coated.