In German, slipper is Hausschuhe, literally “home-shoes”. I have two pairs of shoes, one for the exterior of the house, and one (my slippers) for the interior of the house, because my exterior-shoes are dirty with exterior-things, when my home-shoes stay clean. Cleanliness is the only reason I have slippers.
Again, my bad English makes others laugh, and that makes me happy :-).