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You couldn't be more correct... removing the moisture is the number one solution to mildew problems. In the United States, mold and mildew inhibitors can be purchased in any paint store in either interior and exterior strengths. I can't imagine why you can't obtain them in Indonesia, especially if mold is such a problem.
If they are banned for some reason ( which would explain why they are not available) you should be careful to not break the law by importing them. That having been said, I don't know of any company that would mail order this type of product. However, it would be an easy matter for you to have a friend or relative here in the states just purchase the product here send you a bottle or two.
This type of product is called a "mildewcide", and is available in interior and exterior grades, based on the amount and type of active chemical used. The chemical is added to the paint and the paint shaken thoroughly. One container usually protects one gallon of paint, and it may be added to any paint, oil, alkyd, or latex.
I have another suggestion, and that is to use oil paints instead of latex paints whenever possible. In my experience, oil paints are less attractive to mold and mildew than latex paints. You will be increasing your home's overall resistance to the mold by using them.
There are also some special steps to take in preparing mildewed walls for painting. The mildew must be killed with bleach. You can use a premixed mildew killing product, or DIY by using a mix of 50% household bleach and 50% water. Apply the product to the walls, allow it to remain for a few minutes, and wipe clean. To add some cleaning punch to this mix, add 1/8 cup of TSP (trisodium phosphate) or TSP-substitute to the bleach/water mix. TSP is not legal to use in some states in the US, so it may well be banned in Sumatra, also!
Once the mildew is killed, the walls should be primed with a primer sealer before finish painting. This will reduce the overall porosity of the walls, seal in any stray mildew staining and give you a more even paint finish.
In a quest for particular knowledge, it is sometimes as simple as asking the right question! In this case, the question to ask is "Where is the moisture coming from?"
If the exterior siding is wet much of the time because the moldy side of the house is very shady (or if the entire house is in a damp, wooded area), doing some outside work such as wrapping the house with Tyvek or a similar house wrap and re-siding will indeed be beneficial. Then again, it might be easier (and cheaper) to prune back any foliage near the house or cut down a few trees to allow Mother Nature to do the drying for you... naturally!
However, if the problem is originating inside your home from a
damp basement or crawl space, exterior work will not help. Rather,
moisture proofing the walls and/or floor may show greater results
with less expense. Read our article on damp basements at https://www.naturalhandyman.com/iip/infxtra/infsweat.html
There is also some information about reducing moisture in crawlspaces in our article on mildew at https://www.naturalhandyman.com/iip/infpai/mildew.html#c .
Don't ask... DEMAND that the hole be closed up as soon as possible. More than mold could come through that hole. As a rule, no dwelling should have open holes in any walls except of a temporary nature. I can tell you for sure that your local health department would frown on it! In some areas, that could be enough to have the apartment condemned and the owner heavily fined. The problem is simple... the same sloppy holes that allow pipes to enter your home can also allow an easy path for mice and insects.
Sometimes, especially in older structures, it is impossible to totally conceal pipes within the walls. One repair would be to construct a "box" around the pipes, either from wood or drywall, so that the opening to the wall is totally closed. A removeable door could even be installed if there is reason to believe the repair may need to be redone.
Sometimes, sealing around the pipes is sufficient, but, when the repair is completed, there should be as little space as possible around pipes as possible. Then the remaining small gaps can then be sealed with caulk to keep both dust and vermin out. In some cases it is more effective to fill larger gaps with expanding foam insulation.