The best way to localize is to change only the words, not the way Question is printed (with spaces…):

\makeatletter
\def\AMC@loc@qf#1{\textbf{Pytanie #1:}}
\def\AMC@loc@q#1#2{\textbf{Pytanie #1} #2}
\makeatother

However, if you give me the folowing translations, I can include them in the source file so that with the next release, the package option lang=PL will be available:

\def\AMC@loc@draft{DRAFT}
\def\AMC@loc@message{For your examination, preferably print
  documents compiled from auto-multiple-choice.}
\def\AMC@loc@qf#1{\textbf{Question #1:}}
\def\AMC@loc@q#1#2{\textbf{Question #1} #2}
\def\AMC@loc@corrected{Corrected}
\def\AMC@loc@catalog{Catalog}
\def\AMC@loc@explain{\textit{\textbf{Explanation: }}}
\def\AMC@loc@none{None of these answers are correct.}

Thanks for help.
Please find PL translation below.
Best Regards
Robert

\def\AMC@loc@draft{DRAFT}
PL:\def\AMC@loc@draft{PROJEKT}

For your examination, preferably print documents compiled from auto-multiple-choice
PL:Na potrzeby egzaminu najlepiej jest wydrukować ten dokument skompilowany w programie Auto-Multiple-Choice.

\def\AMC@loc@qf#1{\textbf{Question #1:}}
PL: \def\AMC@loc@qf#1{\textbf{Pytanie #1:}}

\def\AMC@loc@q#1#2{\textbf{Question #1} #2}
PL: \def\AMC@loc@q#1#2{\textbf{Pytanie #1} #2}

\def\AMC@loc@corrected{Corrected}
PL: \def\AMC@loc@corrected{Poprawiony}

\def\AMC@loc@catalog{Catalog}
PL:\def\AMC@loc@catalog{Katalog}

\def\AMC@loc@explain{\textit{\textbf{Explanation: }}}
PL:\def\AMC@loc@explain{\textit{\textbf{Wyjaśnienie: }}}

\def\AMC@loc@none{None of these answers are correct.}
PL:\def\AMC@loc@none{Żadna z powyższych odpowiedzi nie jest poprawna.}
PL:\def\AMC@loc@none{Żadna z powyższych.}

Thank you.

PL:\def\AMC@loc@none{Żadna z powyższych odpowiedzi nie jest poprawna.}
PL:\def\AMC@loc@none{Żadna z powyższych.}

Which is the best?