Only saw this now, just want to add a little bit to what Thomas already said:
folder (album) >>Galerie (= my preference, see above) but other would' may be say:
1 Ordner or 3 Ordner
1Album or 4 Alben
Galerie would be my favorite translation for the frontend, too, because as a visitor you don't want to browse Ordner, which sounds quite bureaucratic. In the backend I feel like the more literal translation Ordner would be more suitable. Album/Alben to me feels a little bit dated, it's not a word that's commonly used a lot anymore except for Fotoalbum maybe, which has kind of a sentimental touch – an Album usually is something that holds treasured memories.
1 picture >>> 1 Bilder
17 pictures >>> 17 Bilder
Small mistake there, singular is 1 Bild.