biodry system

I had the same thing. My problem was that water would accumulate at the base of the wall and humidity would creep up

I have my doubts this would work here, where it rains 3-4 months in a row with high humidity.
You have to eliminate the source of the moisture to get a permanent fix (permanent fixes are possible).

When my house was built, I tarred all the foundations from the base to several inches above ground. I had no salitre anywhere until the French drain on the "water side" of my house plugged up after several years, and rainwater was standing against the side of my house all summer. Then salitre appeared on the inside of that wall.

I had the French drain redone, treated the salitre (a process which takes several months  before repainting if you don't want it coming back), then resealed and repainted and the salitre hasn't come back.

To get rid of the salitre once the cause of the moisture has been remedied, you have to scrape it down, paint it with muriatic acid, rinse the acid off and wait. When you see the salitre starting to form again, you repeat that process until there is no more
salitre coming out for several weeks. Only then can you reseal and repaint the wall.

Another thing I see construction crews do here aside from not sealing foundations is painting the house inside and out right after the walls are finished. It takes months for cement to cure. If you paint right away, you are trapping the moisture in the walls and it has to come out somewhere, hence you get salitre.
My outside walls are not painted at all- we used colored plaster. I waited 6 months to seal those walls with clear sealer, and to seal and paint the interior walls.

Well, I used Prisa Polyprisa Satinado (latex paint) on all my interior walls, 2 coats, after a coat of 5-1 sealer, and haven't had salitre appear anywhere except where the water was standing against my house.

Which is not to say a breathable paint wouldn't be a good idea. It seems like it would help in an already built house that didn't have sealed foundations, that you weren't about to dig up around and seal.

That doesn't bode well for their customer service, does it?

I actually looked up DIY paint-making after Ferret posted this. Most info is really for making small batches of paint for craft projects, furniture, etc. I doubt most people would want to spend the time and effort required to mix up enough paint to paint their walls.