Locale -> LanguageRange conversion to be more general in Android platformResolvedLocale (#21350)

shell/platform/android/io/flutter/plugin/localization/LocalizationPlugin.java

@@ -50,9 +50,15 @@ public class LocalizationPlugin {
       int localeCount = localeList.size();
       for (int index = 0; index < localeCount; ++index) {
         Locale locale = localeList.get(index);
-        String localeString = locale.toString();
-        // This string replacement converts the locale string into the ranges format.
-        languageRanges.add(new Locale.LanguageRange(localeString.replace("_", "-")));
+        // Convert locale string into language range format.
+        String fullRange = locale.getLanguage();
+        if (!locale.getScript().isEmpty()) {
+          fullRange += "-" + locale.getScript();
+        }
+        if (!locale.getCountry().isEmpty()) {
+          fullRange += "-" + locale.getCountry();
+        }
+        languageRanges.add(new Locale.LanguageRange(fullRange));
         languageRanges.add(new Locale.LanguageRange(locale.getLanguage()));
         languageRanges.add(new Locale.LanguageRange(locale.getLanguage() + "-*"));
       }

shell/platform/android/test/io/flutter/plugin/localization/LocalizationPluginTest.java

@@ -120,6 +120,19 @@ public class LocalizationPluginTest {
     assertEquals(result[0], "it");
     assertEquals(result[1], "IT");
     assertEquals(result[2], "");
+
+    supportedLocales =
+        new String[] {
+          "zh", "CN", "Hans",
+          "zh", "HK", "Hant",
+        };
+    localeList = new LocaleList(new Locale("zh", "CN"));
+    when(config.getLocales()).thenReturn(localeList);
+    result = flutterJNI.computePlatformResolvedLocale(supportedLocales);
+    assertEquals(result.length, 3);
+    assertEquals(result[0], "zh");
+    assertEquals(result[1], "CN");
+    assertEquals(result[2], "Hans");
   }
 
   // This test should be synced with the version for API 26.