ADDITIONAL SYSTEM INFORMATION :
openjdk version "11.0.2" 2019-01-15
OpenJDK Runtime Environment 18.9 (build 11.0.2+9)
OpenJDK 64-Bit Server VM 18.9 (build 11.0.2+9, mixed mode)

Using different LocaleProviders does not change the behaviour, i.e. -Djava.locale.providers=COMPAT instead of default.

A DESCRIPTION OF THE PROBLEM :
If you use DecimalFormat to format a double above 1000 with to decimals (12345.78) and german locale the outcome is like with en_US locale ("12,345.78"). Expected is german format like "12.345,78".

REGRESSION : Last worked in version 8u201

STEPS TO FOLLOW TO REPRODUCE THE PROBLEM :
Instantiate DecimalFormat. The way doing it (getInstance or Constructor) does not change behaviour.

EXPECTED VERSUS ACTUAL BEHAVIOR :
EXPECTED -
Expected is a formatted String of an double according to German formatting conventions as described in CLDR i.e. "12.345,78".
ACTUAL -
The String is formatted as en_US, i.e. "12,345.78"

---------- BEGIN SOURCE ----------

import java.text.DecimalFormat;
import java.text.DecimalFormatSymbols;
import java.text.NumberFormat;
import java.util.Locale;
import java.util.ResourceBundle;

public class DecimalFormatTest
{
   private DecimalFormatTest()
   {
      // no instance
   }

   private static final double DOUBLE_TO_FORMAT = 12345.78;

   private static final String EXPECTED_GERMAN_1234578 = "12.345,78";
   private static final String EXPECTED_US_1234578 = "12,345.78";

   public static void main(final String[] args)
   {
      System.out.println(System.getProperty("java.locale.providers"));

      final Locale deDE = new Locale("de", "DE");
      final NumberFormat deFormat1 = NumberFormat.getInstance(deDE);

      final String deDoubleStr1 = deFormat1.format(DecimalFormatTest.DOUBLE_TO_FORMAT);
      System.out.println("DE: " + deDoubleStr1 + " should be " + DecimalFormatTest.EXPECTED_GERMAN_1234578);

      System.setProperty("java.locale.providers", "COMPAT");

      ResourceBundle.clearCache();

      final var deFormat2 = NumberFormat.getNumberInstance(Locale.GERMANY);
      final var deDoubleStr2 = deFormat2.format(DecimalFormatTest.DOUBLE_TO_FORMAT);
      System.out.println("DE: " + deDoubleStr2 + " should be " + DecimalFormatTest.EXPECTED_GERMAN_1234578);

      ResourceBundle.clearCache();

      final Locale locale = Locale.GERMANY;
      final var decFormatSymbolsDE = DecimalFormatSymbols.getInstance(locale);

      final DecimalFormat deFormat3 = new DecimalFormat("#,##0.00", decFormatSymbolsDE);
      final var deDoubleStr3 = deFormat3.format(DecimalFormatTest.DOUBLE_TO_FORMAT);
      System.out.println("DE: " + deDoubleStr3 + " should be " + DecimalFormatTest.EXPECTED_GERMAN_1234578);

      final var decFormatSymbolsUS = DecimalFormatSymbols.getInstance(Locale.US);
      final DecimalFormat usFormat = new DecimalFormat("#,##0.00", decFormatSymbolsUS);
      final var usDoubleStr = usFormat.format(Double.valueOf(DecimalFormatTest.DOUBLE_TO_FORMAT));
      System.out.println("US: " + usDoubleStr + " should be " + DecimalFormatTest.EXPECTED_US_1234578);

   }
}
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FREQUENCY : always