oneThis plural form is used for numbers like: 1
In %1$d day
otherThis plural form is used for numbers like: everything else
In %1$d days
In %1$d day
In %1$d days
Za %1$d dzień
Za %1$d dni
Za %1$d dni
In %1$d day
In %1$d days
Za %1$d dzień
Za %1$d dni
Za %1$d dni
%1$d - number of days, %1$d may be skipped for singular if translation looks better.