That assumes it is unfalsifiable. One of the things it predicts is matter affecting our universe sight unseen. It also would predict some galaxies without dark matter which has just been discovered as well.
Extra dimensions are pretty much the definition of unfalsifiable.
String theory is pure science fiction. It has no relevance whatsoever to the real universe.
String theory and dark matter and extra universes are mysticism. That an conceptual paradigm of the universe should require these things is as clear a sign as one can get that the paradigm is wrong.