The code snippet below illustrates the issue.

Locale loc = Locale.forLanguageTag("zh-Hans-CN");

// Set default locale to en-US
Locale.setDefault(Locale.US);

System.out.println("Default Locale: en-US");
System.out.println(" langauge: " + loc.getDisplayLanguage());
System.out.println(" script: " + loc.getDisplayScript());

// Set DISPLAY locale to zh-Hans-CN
Locale.setDefault(Category.DISPLAY, loc);

System.out.println("Default DISPLAY Locale: zh-Hans-CN");
System.out.println(" langauge: " + loc.getDisplayLanguage());
System.out.println(" script: " + loc.getDisplayScript());

// Set default locale to zh-Hans-CN
Locale.setDefault(loc);

System.out.println("Default Locale: zh-Hans-CN");
System.out.println(" langauge: " + loc.getDisplayLanguage());
System.out.println(" script: " + loc.getDisplayScript());

This code prints out -

Default Locale: en-US
langauge: Chinese
script: Simplified Han
Default DISPLAY Locale: zh-Hans-CN
langauge: ¿¿
script: Simplified Han
Default Locale: zh-Hans-CN
langauge: ¿¿
script: ¿¿¿¿