This translation rule is incorrect. In catalan doesn't exist undecal Rule, I believe that in catalan the translation rule has to be:

"nplurals=3; plural=(n==0 ? 0 : (n==1) ? 1 : 2);" or "nplurals=2; plural=(n==0 ? 0 : 1);"

I will ask to catalan grammar expert which is the correct rule.