I'm in a foreign country, need your help [I'm Affectionate]

where exactly is the smell coming from? I am not an expert so its hard for me to explain this but there is a pipe sometimes that is some kind of air intake for the drain to go down toward the sewer but the top of this pipe is open. this pipe usually has a curve just before the top like a sideway "s" and there needs to be a bit of water in that sideway "s" or else odors can come up the pipe. you might need to just poor a small amount of water in there, like a large glass of water. sorry for the mediocre explanation, I'm not the fixer-uper type, I'm a philosopher.

The reason you will smell smells in a bathroom is because the sewer gas is coming up this is normally stopped by what's known as a p-trap you can Google it and it'll show you all about it you need to make sure that there's always water in the toilet because that blocks the gas from coming up through make sure there's a seal around the bottom of the toilet and if you pull the plug on the bathtub put the plug back in and put a little bit of water over it in the bathtub in the sink and this will block sewer gas from being able to come back up through those pipes

Get a plumber and get the drainage pipes cleared out.

Dish detergent and hot water are better for clogs...

If the pipes are metal, don't use vinegar.