Fun fact - in Polish we have separate forms for 1 (singular), 2-4 (plural but nit many) and everything else. Zero is in “everything else” 0 książek 0.5 książki 1 książka 2,3,4 książki 2.5 książki 5 and above książek 5.5 (any other fraction) książki >100 and a fraction - depends Singular is for one. The first plural is for things kind of treated as individual objects. The second plural is for things that are treated a…
Does Polish also use the same form for 20 as for 0 (i.e. 20 książek)? As I remember it does. If I remember correctly, Polish also differs from Russian in that it only uses the singular for 1, not for all numbers ending in 1 (except 11).
(Note for linguists, it’s not actually quite the genitive, but it’s close enough not to warrant its own case)