ADDITIONAL SYSTEM INFORMATION :
Problem can be reproduced using OpenJDK and AdoptOpenJDK 11 (subversion 11 or 12). OS and hardware plays no role as far as we detected.

A DESCRIPTION OF THE PROBLEM :
When using the -XX:FlightRecorderOptions JVM option in combination with a -Duser.language other than the default the language setting does not have the expected effect leading to malformed weekdays and months output (among other undesired behavior).

REGRESSION : Last worked in version 8u301

STEPS TO FOLLOW TO REPRODUCE THE PROBLEM :
Run the executable test case code in two situations:
1. java -ea -Duser.language=nl FRO11Bug
2. java -ea -Duser.language=nl -XX:FlightRecorderOptions=stackdepth=256 FRO11Bug

The bottom situation "introduces" the bug.

EXPECTED VERSUS ACTUAL BEHAVIOR :
EXPECTED -
dinsdag 28 september 2021

ACTUAL -
Tue 28 Sep 2021 + AssertionError

---------- BEGIN SOURCE ----------
import java.text.SimpleDateFormat;
import java.util.Date;

public class JFR11Bug {

public static void main(String[] args)

{ String pattern = "EEEEEE dd MMMM yyyy"; SimpleDateFormat simpleDateFormat = new SimpleDateFormat(pattern); String date = simpleDateFormat.format(new Date()); System.out.println(date); assert(date.contains("dinsdag")); }

}

---------- END SOURCE ----------

CUSTOMER SUBMITTED WORKAROUND :
Revert to Java8 or upgrade to Java16+. Potentially use different JRE/JDK distributions/versions than the above mentioned.

FREQUENCY : always