如何获取java中未定义的语言环境DisplayName

Locale customLocale = new Locale("xx", "XX"); // 自定义的未定义语言环境
String displayName = customLocale.getDisplayName();
System.out.println(displayName);

ResourceBundle customBundle = ResourceBundle.getBundle("CustomBundle", new Locale("xx", "XX")); // 自定义的未定义语言环境资源文件
Locale customLocale = customBundle.getLocale();
String displayName = customLocale.getDisplayName();
System.out.println(displayName);