FULL PRODUCT VERSION :
JDK 6: 1.6.0.29
JDK 7: 1.7.0

ADDITIONAL OS VERSION INFORMATION :
Windows XP Professional SP3

A DESCRIPTION OF THE PROBLEM :
The dateformats both for polish and polish-Poland (pl/pl_PL) are wrong.

Current formats from FormatData:

FormatData_pl:
"d MMMM yyyy", // long date pattern
"yyyy-MM-dd", // medium date pattern
"yy-MM-dd", // short date pattern

FormatData_pl_PL:
"d MMMM yyyy", // long date pattern
"yyyy-MM-dd", // medium date pattern
"dd.MM.yy", // short date pattern

According to http://unicode.org/repos/cldr-tmp/trunk/diff/summary/pl.html the following format are correct:
date-long: d MMMM y
date-medium: d MMM y
date-short: dd.MM.yyyy

So the correct version in java-datestyle for both pl and pl_PL is:
"d MMMM yyyy", // long date pattern
"dd.MM.yyyy", // medium date pattern
"dd.MM.yy", // short date pattern


REPRODUCIBILITY :
This bug can be reproduced always.

---------- BEGIN SOURCE ----------
import java.text.DateFormat;
import java.util.Date;
import java.util.Locale;

public class PlLocale {
public static void main(String[] args) {
testLocale(new Locale("pl", "PL"));
testLocale(new Locale("pl"));
}

// prints the short/medium/long date format for the given locale
private static void testLocale(Locale locale) {
System.out.format("--- %s ---\n", locale.getDisplayName());

// wrong for pl, correct for pl_PL
DateFormat df = DateFormat.getDateInstance(DateFormat.SHORT, locale);
System.out.println(df.format(new Date()));

// wrong for pl and pl_PL
df = DateFormat.getDateInstance(DateFormat.MEDIUM, locale);
System.out.println(df.format(new Date()));

// correct
df = DateFormat.getDateInstance(DateFormat.LONG, locale);
System.out.println(df.format(new Date()));
}
}
---------- END SOURCE ----------