Expose Locale to method validation in WebFlux

Closes gh-33810

spring-webflux/src/main/java/org/springframework/web/reactive/result/method/InvocableHandlerMethod.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2024 the original author or authors.
+ * Copyright 2002-2025 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -39,6 +39,7 @@ import reactor.core.publisher.Mono;
 import reactor.core.publisher.SynchronousSink;
 import reactor.core.scheduler.Scheduler;
 
+import org.springframework.context.i18n.LocaleContextHolder;
 import org.springframework.core.CoroutinesUtils;
 import org.springframework.core.DefaultParameterNameDiscoverer;
 import org.springframework.core.KotlinDetector;
@@ -186,8 +187,14 @@ public class InvocableHandlerMethod extends HandlerMethod {
 
 		return getMethodArgumentValuesOnScheduler(exchange, bindingContext, providedArgs).flatMap(args -> {
 			if (shouldValidateArguments() && this.methodValidator != null) {
-				this.methodValidator.applyArgumentValidation(
-						getBean(), getBridgedMethod(), getMethodParameters(), args, this.validationGroups);
+				try {
+					LocaleContextHolder.setLocaleContext(exchange.getLocaleContext());
+					this.methodValidator.applyArgumentValidation(
+							getBean(), getBridgedMethod(), getMethodParameters(), args, this.validationGroups);
+				}
+				finally {
+					LocaleContextHolder.resetLocaleContext();
+				}
 			}
 			Object value;
 			Method method = getBridgedMethod();