diff --git a/spring-core-test/src/main/java/org/springframework/core/test/tools/TestCompiler.java b/spring-core-test/src/main/java/org/springframework/core/test/tools/TestCompiler.java
index 5d4b04ea75b0..ba88738f2f21 100644
--- a/spring-core-test/src/main/java/org/springframework/core/test/tools/TestCompiler.java
+++ b/spring-core-test/src/main/java/org/springframework/core/test/tools/TestCompiler.java
@@ -53,6 +53,8 @@ public final class TestCompiler {
 
 	private final JavaCompiler compiler;
 
+	private final Locale locale;
+
 	private final SourceFiles sourceFiles;
 
 	private final ResourceFiles resourceFiles;
@@ -64,12 +66,13 @@ public final class TestCompiler {
 	private final List<String> compilerOptions;
 
 
-	private TestCompiler(@Nullable ClassLoader classLoader, JavaCompiler compiler,
-			SourceFiles sourceFiles, ResourceFiles resourceFiles, ClassFiles classFiles,
-			List<Processor> processors, List<String> compilerOptions) {
+	private TestCompiler(@Nullable ClassLoader classLoader, JavaCompiler compiler, Locale locale,
+			SourceFiles sourceFiles, ResourceFiles resourceFiles, ClassFiles classFiles, List<Processor> processors,
+			List<String> compilerOptions) {
 
 		this.classLoader = classLoader;
 		this.compiler = compiler;
+		this.locale = locale;
 		this.sourceFiles = sourceFiles;
 		this.resourceFiles = resourceFiles;
 		this.classFiles = classFiles;
@@ -92,8 +95,9 @@ public static TestCompiler forSystem() {
 	 * @return a new {@code TestCompiler} instance
 	 */
 	public static TestCompiler forCompiler(JavaCompiler javaCompiler) {
-		return new TestCompiler(null, javaCompiler, SourceFiles.none(),
-				ResourceFiles.none(), ClassFiles.none(), Collections.emptyList(), Collections.emptyList());
+		return new TestCompiler(null, javaCompiler, Locale.getDefault(),
+				SourceFiles.none(), ResourceFiles.none(),
+				ClassFiles.none(), Collections.emptyList(), Collections.emptyList());
 	}
 
 	/**
@@ -105,13 +109,26 @@ public TestCompiler with(UnaryOperator<TestCompiler> customizer) {
 		return customizer.apply(this);
 	}
 
+	/**
+	 * Create a new {@code TestCompiler} instance that uses the specified {@link Locale}
+	 * to render compiler messages.
+	 * @param locale the locale to use
+	 * @return a new {@code TestCompiler} instance
+	 * @since 6.1
+	 */
+	public TestCompiler withLocale(Locale locale) {
+		return new TestCompiler(this.classLoader, this.compiler, locale,
+				this.sourceFiles, this.resourceFiles,
+				this.classFiles, this.processors, this.compilerOptions);
+	}
+
 	/**
 	 * Create a new {@code TestCompiler} instance with additional source files.
 	 * @param sourceFiles the additional source files
 	 * @return a new {@code TestCompiler} instance
 	 */
 	public TestCompiler withSources(SourceFile... sourceFiles) {
-		return new TestCompiler(this.classLoader, this.compiler,
+		return new TestCompiler(this.classLoader, this.compiler, this.locale,
 				this.sourceFiles.and(sourceFiles), this.resourceFiles,
 				this.classFiles, this.processors, this.compilerOptions);
 	}
@@ -122,7 +139,7 @@ public TestCompiler withSources(SourceFile... sourceFiles) {
 	 * @return a new {@code TestCompiler} instance
 	 */
 	public TestCompiler withSources(Iterable<SourceFile> sourceFiles) {
-		return new TestCompiler(this.classLoader, this.compiler,
+		return new TestCompiler(this.classLoader, this.compiler, this.locale,
 				this.sourceFiles.and(sourceFiles), this.resourceFiles,
 				this.classFiles, this.processors, this.compilerOptions);
 	}
@@ -133,7 +150,7 @@ public TestCompiler withSources(Iterable<SourceFile> sourceFiles) {
 	 * @return a new {@code TestCompiler} instance
 	 */
 	public TestCompiler withSources(SourceFiles sourceFiles) {
-		return new TestCompiler(this.classLoader, this.compiler,
+		return new TestCompiler(this.classLoader, this.compiler, this.locale,
 				this.sourceFiles.and(sourceFiles), this.resourceFiles,
 				this.classFiles, this.processors, this.compilerOptions);
 	}
@@ -144,9 +161,9 @@ public TestCompiler withSources(SourceFiles sourceFiles) {
 	 * @return a new {@code TestCompiler} instance
 	 */
 	public TestCompiler withResources(ResourceFile... resourceFiles) {
-		return new TestCompiler(this.classLoader, this.compiler, this.sourceFiles,
-				this.resourceFiles.and(resourceFiles), this.classFiles, this.processors,
-				this.compilerOptions);
+		return new TestCompiler(this.classLoader, this.compiler, this.locale,
+				this.sourceFiles, this.resourceFiles.and(resourceFiles),
+				this.classFiles, this.processors, this.compilerOptions);
 	}
 
 	/**
@@ -155,9 +172,9 @@ public TestCompiler withResources(ResourceFile... resourceFiles) {
 	 * @return a new {@code TestCompiler} instance
 	 */
 	public TestCompiler withResources(Iterable<ResourceFile> resourceFiles) {
-		return new TestCompiler(this.classLoader, this.compiler, this.sourceFiles,
-				this.resourceFiles.and(resourceFiles), this.classFiles, this.processors,
-				this.compilerOptions);
+		return new TestCompiler(this.classLoader, this.compiler, this.locale,
+				this.sourceFiles, this.resourceFiles.and(resourceFiles),
+				this.classFiles, this.processors, this.compilerOptions);
 	}
 
 	/**
@@ -166,9 +183,9 @@ public TestCompiler withResources(Iterable<ResourceFile> resourceFiles) {
 	 * @return a new {@code TestCompiler} instance
 	 */
 	public TestCompiler withResources(ResourceFiles resourceFiles) {
-		return new TestCompiler(this.classLoader, this.compiler, this.sourceFiles,
-				this.resourceFiles.and(resourceFiles), this.classFiles, this.processors,
-				this.compilerOptions);
+		return new TestCompiler(this.classLoader, this.compiler, this.locale,
+				this.sourceFiles, this.resourceFiles.and(resourceFiles),
+				this.classFiles, this.processors, this.compilerOptions);
 	}
 
 	/**
@@ -177,9 +194,9 @@ public TestCompiler withResources(ResourceFiles resourceFiles) {
 	 * @return a new {@code TestCompiler} instance
 	 */
 	public TestCompiler withClasses(Iterable<ClassFile> classFiles) {
-		return new TestCompiler(this.classLoader, this.compiler, this.sourceFiles,
-				this.resourceFiles, this.classFiles.and(classFiles), this.processors,
-				this.compilerOptions);
+		return new TestCompiler(this.classLoader, this.compiler, this.locale,
+				this.sourceFiles, this.resourceFiles, this.classFiles.and(classFiles),
+				this.processors, this.compilerOptions);
 	}
 
 	/**
@@ -190,8 +207,9 @@ public TestCompiler withClasses(Iterable<ClassFile> classFiles) {
 	public TestCompiler withProcessors(Processor... processors) {
 		List<Processor> mergedProcessors = new ArrayList<>(this.processors);
 		mergedProcessors.addAll(Arrays.asList(processors));
-		return new TestCompiler(this.classLoader, this.compiler, this.sourceFiles,
-				this.resourceFiles, this.classFiles, mergedProcessors, this.compilerOptions);
+		return new TestCompiler(this.classLoader, this.compiler, this.locale,
+				this.sourceFiles, this.resourceFiles, this.classFiles, mergedProcessors,
+				this.compilerOptions);
 	}
 
 	/**
@@ -202,8 +220,9 @@ public TestCompiler withProcessors(Processor... processors) {
 	public TestCompiler withProcessors(Iterable<Processor> processors) {
 		List<Processor> mergedProcessors = new ArrayList<>(this.processors);
 		processors.forEach(mergedProcessors::add);
-		return new TestCompiler(this.classLoader, this.compiler, this.sourceFiles,
-				this.resourceFiles, this.classFiles, mergedProcessors, this.compilerOptions);
+		return new TestCompiler(this.classLoader, this.compiler, this.locale,
+				this.sourceFiles, this.resourceFiles, this.classFiles,
+				mergedProcessors, this.compilerOptions);
 	}
 
 	/**
@@ -215,8 +234,9 @@ public TestCompiler withProcessors(Iterable<Processor> processors) {
 	public TestCompiler withCompilerOptions(String... options) {
 		List<String> mergedCompilerOptions = Stream.concat(this.compilerOptions.stream(),
 				Arrays.stream(options)).distinct().toList();
-		return new TestCompiler(this.classLoader, this.compiler, this.sourceFiles,
-				this.resourceFiles, this.classFiles, this.processors, mergedCompilerOptions);
+		return new TestCompiler(this.classLoader, this.compiler, this.locale,
+				this.sourceFiles, this.resourceFiles, this.classFiles,
+				this.processors, mergedCompilerOptions);
 	}
 
 	/**
@@ -308,7 +328,7 @@ private DynamicClassLoader compile() {
 		DynamicJavaFileManager fileManager = new DynamicJavaFileManager(
 				standardFileManager, classLoaderToUse, this.classFiles, this.resourceFiles);
 		if (!this.sourceFiles.isEmpty()) {
-			Errors errors = new Errors();
+			Errors errors = new Errors(this.locale);
 			CompilationTask task = this.compiler.getTask(null, fileManager, errors,
 					this.compilerOptions, null, compilationUnits);
 			if (!this.processors.isEmpty()) {
@@ -349,13 +369,19 @@ public TestCompiler printFiles(PrintStream printStream) {
 	 */
 	static class Errors implements DiagnosticListener<JavaFileObject> {
 
+		private final Locale locale;
+
 		private final StringBuilder message = new StringBuilder();
 
+		Errors(Locale locale) {
+			this.locale = locale;
+		}
+
 		@Override
 		public void report(Diagnostic<? extends JavaFileObject> diagnostic) {
 			if (diagnostic.getKind() == Diagnostic.Kind.ERROR) {
 				this.message.append('\n');
-				this.message.append(diagnostic.getMessage(Locale.getDefault()));
+				this.message.append(diagnostic.getMessage(this.locale));
 				if (diagnostic.getSource() != null) {
 					this.message.append(' ');
 					this.message.append(diagnostic.getSource().getName());
diff --git a/spring-core-test/src/test/java/org/springframework/core/test/tools/TestCompilerTests.java b/spring-core-test/src/test/java/org/springframework/core/test/tools/TestCompilerTests.java
index c921a728553d..c91cdcb3271b 100644
--- a/spring-core-test/src/test/java/org/springframework/core/test/tools/TestCompilerTests.java
+++ b/spring-core-test/src/test/java/org/springframework/core/test/tools/TestCompilerTests.java
@@ -19,6 +19,7 @@
 import java.io.InputStream;
 import java.util.ArrayList;
 import java.util.List;
+import java.util.Locale;
 import java.util.Set;
 import java.util.function.Supplier;
 
@@ -170,8 +171,8 @@ public static void main(String[] args) {
 				}
 				""");
 		assertThatExceptionOfType(CompilationException.class).isThrownBy(
-				() -> TestCompiler.forSystem().failOnWarning().withSources(
-						SourceFile.of(HELLO_DEPRECATED), main).compile(compiled -> {
+				() -> TestCompiler.forSystem().failOnWarning().withLocale(Locale.ENGLISH)
+						.withSources(SourceFile.of(HELLO_DEPRECATED), main).compile(compiled -> {
 				})).withMessageContaining("warnings found and -Werror specified");
 	}