If the sewage is backing up, I dont know that you can get rid of the smell until they fix it. You can try and cover it up with a lysol kind of thing, I wouldn't light any candles or anything..

This is because Chinese "plumbers" don't believe in using any kind of trap. So without that barrier of water, you get a nice straight shot to the sewage below. Most fresheners aren't strong enough to completely cover the smell (so you'll just have a sewage smell with a hint of roses). You could put out a tray of vinegar to cover the smell, but then you'd have to be able to stand everything smelling like vinegar.

It is something you have to live with unforntunately, a newer building with proper plumbing will be the only way to over-come this problem. I would suggest that a plumber would not be able to fix it because it would be a major job as all the pipes are part of the internal structure

All of the above. You can try to constantly pour bleach or soap down the drain, but that's only to cover the problem.

A trap, so simple and efficient is apparently beyond the plumbing geniuses here. Whenever you smell the crap, just hold your nose, say to yourself, "This is China" and move on.

There is a pretty low-tech fix: take a plastic bag which can hold liquids without leaking, fill it part way (not full) with water, push out all the extra air, and tie it off. Place it over the offending drain and it will expand to seal any airflow in or out, cutting off the source of said foul smell. You might need to experiment a little bit with the size of the bag and amount of water. Then just kick it aside when you take a shower, and you might want to mop up the floor after.