Australia

There's a good argument to be made for intuitive design. Red means danger, green means safe. That's a pretty worldwide understanding. Yellow means caution; that's a little less universal, but still pretty common.

There are, in my opinion, good reasons to not say "safe" at the beach under any circumstances, so I don't think using green flags is a great idea, but that doesn't mean some other form of tweaking is inappropriate.

The only thing worth doing is adding a few common international languages

The problem with this, as the article says, is getting the translations right. To convey the message properly. "Shore dump" is currently being translated into Chinese as "beachside rubbish tip", and "shore break" is being translated into Korean as "shore relaxation". And many people are already seeing "swim between the flags" as an indication that people doing serious swimming (e.g. swimming laps) are the only ones who should be between the flags.

In Dutch, they have two words for cyclists: fietser (cyclist) for the average person using a bike to get around, and "wielrenner" (literally, "wheel runner") for people doing cycling as sport. I wonder if a similar language difference might be a problem here with "swim". We normally use it for anything in the water, but some people are obviously interpreting it as more like the aquatic equivalent of the wielrenner.

It's not an insurmountable problem, but it is a difficult one.

Plus: most people don't read signs. So it's not a bad idea to make the symbols as self-explanatory as possible.

The effectiveness of the red and yellow patrol flags is unequivocal as there have been no recorded coastal drowning fatalities this summer or in the previous year between the flags.

Oof. That is...not the slam dunk they think it is. The whole point of the critique is that evidence shows many people don't realise they're supposed to swim between the flags.

Now, I'm not fully on board with the reporting of the Guardian here either. The studies they cite talk about people misunderstanding the signs and flags, but they don't say anything about what people actually do in response to this. If they misunderstand the sign and then just ignore it and swim between the flags because that's where everyone is anyway, then there isn't much of a problem. If, on the other hand, the confusion causes them to either make a conscious decision to swim away from the patrolled areas, or to throw up their arms and go "well I dunno what I'm supposed to do" (and then either decide against swimming at all, or decide that swimming outside the patrolled areas is fine), then it's a significant problem. But we don't know, based on these studies, which of those is happening.

The Guardian's suggestion of using green flags is a silly one, but the study they cited just before that, where pictograms of a lifesaver were put on top of the classic red and yellow flag, could be a good idea to follow.