With the fix of JDK-8218781, the localized Japanese Era names are introduced 
in Chinese and Korean locales in the COMPAT provider. 

However, using the CLDR provider, the Japanese Era is not displayed in these 
locales.  The CLDR provider is not default in JDK 8 but this changes need to 
be applied to the CLDR provider to avoid inconsistency between both locale providers. 

$ cat LocalizedEra.java 
import java.util.*; 
import java.time.*; 
import java.time.chrono.*; 
import java.time.format.*; 
import java.time.temporal.*; 
import static java.util.Calendar.*; 
import static java.util.Locale.*; 

public class LocalizeEra { 
  public static void main(String[] args) { 
    Calendar c = new Calendar.Builder() 
            .setCalendarType("japanese") 
            .setFields(ERA, 5, YEAR, 1, MONTH, MAY, DAY_OF_MONTH, 1) 
            .build(); 

        String ja_l = c.getDisplayName(ERA, LONG, (Locale)JAPAN); 
        String ja_s = c.getDisplayName(ERA, SHORT, (Locale)JAPAN); 
        String ch_l = c.getDisplayName(ERA, LONG, (Locale)CHINA); 
        String ch_s = c.getDisplayName(ERA, SHORT, (Locale)CHINA); 
        String ko_l = c.getDisplayName(ERA, LONG, (Locale)KOREA); 
        String ko_s = c.getDisplayName(ERA, SHORT, (Locale)KOREA); 

        System.out.println("Japanese - " + ja_l + " - " + ja_s); 
        System.out.println("Chinese - " + ch_l + " - " + ch_s); 
        System.out.println("Korean - " + ko_l + " - " + ko_s); 
   } 
} 

$ jdk1.8.0_221_x64/bin/java  -Djava.locale.providers=COMPAT LocalizeEra
Japanese - ������ - R
Chinese - ������ - R
Korean - ��������� - R

$ jdk1.8.0_221_x64/bin/java -Djava.locale.providers=CLDR LocalizeEra 
Japanese - Reiwa - ������
Chinese - Reiwa -
Korean - Reiwa -