Ouh sorry yes you are right.
But the correction is necessary for:
lib/pkp/locale/en_US/countries.xml add line
<country name="Serbia and Montenegro" code="CS"/>
and in
lib/pkp/locale/pl_PL/countries.xml change
<country name="Serbia" code="CS"/>
to <country name="Serbia" code="RS"/> and add
<country name="Serbia i Czarnogóra" code="CS"/>
Regards