Address Guillaume's comments

Author: zakkak

core/deployment/src/main/java/io/quarkus/deployment/steps/LocaleProcessor.java

@@ -116,7 +116,7 @@ public boolean getAsBoolean() {
      */
     @Deprecated
     public static String nativeImageUserLanguage(NativeConfig nativeConfig, LocalesBuildTimeConfig localesBuildTimeConfig) {
-        String language = LocalesBuildTimeConfig.DEFAULT_LANGUAGE;
+        String language = System.getProperty("user.language", "en");
         if (localesBuildTimeConfig.defaultLocale.isPresent()) {
             language = localesBuildTimeConfig.defaultLocale.get().getLanguage();
         }
@@ -140,7 +140,7 @@ public static String nativeImageUserLanguage(NativeConfig nativeConfig, LocalesB
      */
     @Deprecated
     public static String nativeImageUserCountry(NativeConfig nativeConfig, LocalesBuildTimeConfig localesBuildTimeConfig) {
-        String country = LocalesBuildTimeConfig.DEFAULT_COUNTRY;
+        String country = System.getProperty("user.country", "");
         if (localesBuildTimeConfig.defaultLocale.isPresent()) {
             country = localesBuildTimeConfig.defaultLocale.get().getCountry();
         }

core/deployment/src/main/java/io/quarkus/deployment/steps/NativeImageFeatureStep.java

@@ -93,23 +93,17 @@ public void write(String s, byte[] bytes) {
         overallCatch.invokeStaticMethod(BUILD_TIME_INITIALIZATION,
                 overallCatch.marshalAsArray(String.class, overallCatch.load(""))); // empty string means initialize everything
 
+        ResultHandle graalVMVersion = overallCatch.invokeStaticMethod(GRAALVM_VERSION_GET_CURRENT);
+        // Set the user.language and user.country system properties to the default locale
         // The deprecated option takes precedence for users who are already using it.
         if (nativeConfig.userLanguage().isPresent()) {
             overallCatch.invokeStaticMethod(REGISTER_RUNTIME_SYSTEM_PROPERTIES,
                     overallCatch.load("user.language"), overallCatch.load(nativeConfig.userLanguage().get()));
-            if (nativeConfig.userCountry().isPresent()) {
-                overallCatch.invokeStaticMethod(REGISTER_RUNTIME_SYSTEM_PROPERTIES,
-                        overallCatch.load("user.country"), overallCatch.load(nativeConfig.userCountry().get()));
-            }
         } else if (localesBuildTimeConfig.defaultLocale.isPresent()) {
             overallCatch.invokeStaticMethod(REGISTER_RUNTIME_SYSTEM_PROPERTIES,
                     overallCatch.load("user.language"),
                     overallCatch.load(localesBuildTimeConfig.defaultLocale.get().getLanguage()));
-            overallCatch.invokeStaticMethod(REGISTER_RUNTIME_SYSTEM_PROPERTIES,
-                    overallCatch.load("user.country"),
-                    overallCatch.load(localesBuildTimeConfig.defaultLocale.get().getCountry()));
         } else {
-            ResultHandle graalVMVersion = overallCatch.invokeStaticMethod(GRAALVM_VERSION_GET_CURRENT);
             BranchResult graalVm24_2Test = overallCatch
                     .ifGreaterEqualZero(overallCatch.invokeVirtualMethod(GRAALVM_VERSION_COMPARE_TO, graalVMVersion,
                             overallCatch.marshalAsArray(int.class, overallCatch.load(24), overallCatch.load(2))));
@@ -118,6 +112,22 @@ public void write(String s, byte[] bytes) {
                 greaterEqual24_2.invokeStaticMethod(REGISTER_RUNTIME_SYSTEM_PROPERTIES,
                         greaterEqual24_2.load("user.language"),
                         greaterEqual24_2.load("en"));
+            }
+        }
+        // The deprecated option takes precedence for users who are already using it.
+        if (nativeConfig.userCountry().isPresent()) {
+            overallCatch.invokeStaticMethod(REGISTER_RUNTIME_SYSTEM_PROPERTIES,
+                    overallCatch.load("user.country"), overallCatch.load(nativeConfig.userCountry().get()));
+        } else if (localesBuildTimeConfig.defaultLocale.isPresent()) {
+            overallCatch.invokeStaticMethod(REGISTER_RUNTIME_SYSTEM_PROPERTIES,
+                    overallCatch.load("user.country"),
+                    overallCatch.load(localesBuildTimeConfig.defaultLocale.get().getCountry()));
+        } else {
+            BranchResult graalVm24_2Test = overallCatch
+                    .ifGreaterEqualZero(overallCatch.invokeVirtualMethod(GRAALVM_VERSION_COMPARE_TO, graalVMVersion,
+                            overallCatch.marshalAsArray(int.class, overallCatch.load(24), overallCatch.load(2))));
+            /* GraalVM >= 24.2 */
+            try (BytecodeCreator greaterEqual24_2 = graalVm24_2Test.trueBranch()) {
                 greaterEqual24_2.invokeStaticMethod(REGISTER_RUNTIME_SYSTEM_PROPERTIES,
                         greaterEqual24_2.load("user.country"),
                         greaterEqual24_2.load("US"));

core/runtime/src/main/java/io/quarkus/runtime/LocalesBuildTimeConfig.java

@@ -51,6 +51,6 @@ public class LocalesBuildTimeConfig {
      * Defaults to the JVM's default locale if not set. Starting with GraalVM for JDK 24, it defaults to {@code en-US}
      * for native executables.
      */
-    @ConfigItem(defaultValue = DEFAULT_LANGUAGE + "-" + DEFAULT_COUNTRY, defaultValueDocumentation = "Build system locale")
+    @ConfigItem()
     public Optional<Locale> defaultLocale;
 }