China Southern, and Chinese airlines in general have OK IT - better than BA - but you need to understand websites are not their main route to market, everything in China is done in apps usually in WeChat, and websites only get a minority of overall customer traffic. They therefore don't get the focus that their apps do.

Using trip.com for booking Chinese airlines is usually a decent compromise, they have functional and decent customer service (they actually pick up the phone 24hrs a day and have agents who can handle English) and can provide the buffer between you can Chinese airlines and their bluesky GDS backend. Whilst many on here will bang the drum to book direct with the airline, and generally that's true, using trip.com for anything China related is a sensible path that can add value.