oneThis plural form is used for numbers like: 1
Every %1$d week, on %2$s
otherThis plural form is used for numbers like: everything else
Every %1$d weeks, on %2$s
Every %1$d week, on %2$s
Every %1$d weeks, on %2$s
Every %1$d week, on %2$s
Every %1$d weeks, on %2$s
%1$d - number, %1$d may be skipped for singular if translation looks better.
%2$s - name of week day