diff --git a/xapi-model/src/main/java/dev/learning/xapi/model/validation/internal/validators/LocaleValidator.java b/xapi-model/src/main/java/dev/learning/xapi/model/validation/internal/validators/LocaleValidator.java
index 85b5dcd0..e371fcd3 100644
--- a/xapi-model/src/main/java/dev/learning/xapi/model/validation/internal/validators/LocaleValidator.java
+++ b/xapi-model/src/main/java/dev/learning/xapi/model/validation/internal/validators/LocaleValidator.java
@@ -12,6 +12,11 @@
 
 /**
  * The Locale being validated must have a ISO3 Language and Country.
+ * <p>
+ * There is no way to reliably test a locale that was instantiated with
+ * {@link Locale.forLanguageTag}. {@link Locale.forLanguageTag} treats most invalid locales as
+ * undetermined (und).
+ * </p>
  *
  * @author István Rátkai (Selindek)
  * @author Thomas Turrell-Croft
@@ -36,10 +41,7 @@ public boolean isValid(Locale locale, ConstraintValidatorContext context) {
       final var blar = Locale.forLanguageTag(locale.toString());
 
       try {
-        blar.getISO3Language();
-        blar.getISO3Country();
-
-        return true;
+        return !blar.getISO3Language().equals("");
       } catch (final MissingResourceException e2) {
 
         return false;
diff --git a/xapi-model/src/test/java/dev/learning/xapi/model/ActivityTests.java b/xapi-model/src/test/java/dev/learning/xapi/model/ActivityTests.java
index b1a97760..2482c34a 100644
--- a/xapi-model/src/test/java/dev/learning/xapi/model/ActivityTests.java
+++ b/xapi-model/src/test/java/dev/learning/xapi/model/ActivityTests.java
@@ -5,13 +5,18 @@
 package dev.learning.xapi.model;
 
 import static org.hamcrest.MatcherAssert.assertThat;
+import static org.hamcrest.Matchers.hasSize;
 import static org.hamcrest.Matchers.instanceOf;
 import static org.hamcrest.Matchers.is;
 
 import com.fasterxml.jackson.databind.ObjectMapper;
+import jakarta.validation.ConstraintViolation;
+import jakarta.validation.Validation;
+import jakarta.validation.Validator;
 import java.io.IOException;
 import java.net.URI;
 import java.util.Locale;
+import java.util.Set;
 import org.junit.jupiter.api.DisplayName;
 import org.junit.jupiter.api.Test;
 import org.springframework.util.ResourceUtils;
@@ -27,6 +32,8 @@ class ActivityTests {
 
   private final ObjectMapper objectMapper = new ObjectMapper().findAndRegisterModules();
 
+  private final Validator validator = Validation.buildDefaultValidatorFactory().getValidator();
+
   @Test
   void whenDeserializingActivityThenResultIsInstanceOfActivity() throws Exception {
 
@@ -138,12 +145,31 @@ void whenActivityIsConstructedWithIdThenIdIsExpected() {
   void whenActivityIsBuiltWithStringIdThenIdIsExpected() {
 
     // When Activity Is Built With String Id
-    final var activity =
-        Activity.builder().id("http://www.example.co.uk/exampleactivity").build();
+    final var activity = Activity.builder().id("http://www.example.co.uk/exampleactivity").build();
 
     // Then Id Is Expected
     assertThat(activity.getId(), is(URI.create("http://www.example.co.uk/exampleactivity")));
 
   }
 
+  @Test
+  void whenValidatingActivityWithInvalidDisplayThenConstraintViolationsSizeIsOne()
+      throws Exception {
+
+    // This test uses Jackson to read the JSON because we need to test that Jackson does not use
+    // Locale.forLanguageTag. Currently forLanguageTag is very permissive and will treat most
+    // invalid strings as und.
+    final var json =
+        "{\"objectType\":\"Activity\",\"id\":\"https://example.com/activity/simplestatement\",\"definition\":{\"name\":{\"a12345678\":\"Simple Statement\"}}}";
+
+    final var activity = objectMapper.readValue(json, Activity.class);
+
+    // When Validating Activity With Invalid Display
+    final Set<ConstraintViolation<Activity>> constraintViolations = validator.validate(activity);
+
+    // Then ConstraintViolations Size Is One
+    assertThat(constraintViolations, hasSize(1));
+
+  }
+
 }
diff --git a/xapi-model/src/test/java/dev/learning/xapi/model/validation/internal/validators/LocaleValidatorTests.java b/xapi-model/src/test/java/dev/learning/xapi/model/validation/internal/validators/LocaleValidatorTests.java
index 31dc80a7..0ba53d65 100644
--- a/xapi-model/src/test/java/dev/learning/xapi/model/validation/internal/validators/LocaleValidatorTests.java
+++ b/xapi-model/src/test/java/dev/learning/xapi/model/validation/internal/validators/LocaleValidatorTests.java
@@ -34,9 +34,9 @@ void whenValueIsNullThenResultIsTrue() {
   }
 
   @Test
-  void whenCallingIsValidOnLocaleWithUKKeyThenResultIsTrue() {
+  void whenCallingIsValidOnUKLocaleThenResultIsTrue() {
 
-    // When Calling Is Valid On Locale With UK Key
+    // When Calling Is Valid On UK Locale
     final var result = validator.isValid(Locale.UK, null);
 
     // Then Result Is True
@@ -44,9 +44,9 @@ void whenCallingIsValidOnLocaleWithUKKeyThenResultIsTrue() {
   }
 
   @Test
-  void whenCallingIsValidOnLocaleWithENKeyThenResultIsTrue() {
+  void whenCallingIsValidOnENLocaleThenResultIsTrue() {
 
-    // When Calling Is Valid On Locale With EN Key
+    // When Calling Is Valid On EN Locale
     final var result = validator.isValid(Locale.ENGLISH, null);
 
     // Then Result Is True
@@ -54,51 +54,54 @@ void whenCallingIsValidOnLocaleWithENKeyThenResultIsTrue() {
   }
 
   @Test
-  void whenCallingIsValidOnLocaleWithENAndUKKeysThenResultIsTrue() {
+  void whenCallingIsValidOnUSLocaleThenResultIsTrue() {
 
-    // When Calling Is Valid On Locale With EN And UK Keys
-    final var result = validator.isValid(Locale.UK, null);
+    // When Calling Is Valid On US Locale
+    final var result = validator.isValid(Locale.US, null);
 
     // Then Result Is True
     assertTrue(result);
   }
 
-  @Test
-  void whenCallingIsValidOnLocaleWithENAndUnknownKeysThenResultIsFalse() {
+  @ParameterizedTest
+  @ValueSource(strings = {"und", "zh-CHS", "zh-CN", "zh-Hans", "zh-Hant", "zh-HK"})
+  void whenCallingIsValidOnLocaleWithValidLanguageTagThenResultIsTrue(String arg) {
 
-    // When Calling Is Valid On Locale With EN And Unknown Keys
-    final var result = validator.isValid(Locale.forLanguageTag("unknown"), null);
+    // When Calling Is Valid On Locale With Valid Language Tag
+    final var result = validator.isValid(Locale.forLanguageTag(arg), null);
 
-    // Then Result Is False
-    assertFalse(result);
+    // Then Result Is True
+    assertTrue(result);
   }
 
-  @Test
-  void whenCallingIsValidOnLocaleWithChineseSimplifiedKeyUsingForLangugeTagThenResultIsTrue() {
+  @ParameterizedTest
+  @ValueSource(strings = {"unknown"})
+  void whenCallingIsValidOnLocaleWithInvalidLanguageTagThenResultIsFalse(String arg) {
 
-    // When Calling Is Valid On Locale With Chinese Simplified Key
-    final var result = validator.isValid(Locale.forLanguageTag("zh-CHS"), null);
+    // When Calling Is Valid On Locale With Invalid Language Tag
+    final var result = validator.isValid(Locale.forLanguageTag(arg), null);
 
-    // Then Result Is True
-    assertTrue(result);
+    // Then Result Is False
+    assertFalse(result);
   }
 
   @ParameterizedTest
   @ValueSource(strings = {"und", "zh-CHS", "zh-CN", "zh-Hans", "zh-Hant", "zh-HK"})
-  void whenCallingIsValidOnLocaleWithValidKeyThenResultIsTrue(String arg) {
+  void whenCallingIsValidOnLocaleWithValidLanguageThenResultIsTrue(String arg) {
 
-    // When Calling Is Valid On Locale With Valid Key
+    // when Calling Is Valid On Locale With Valid Language
     final var result = validator.isValid(new Locale(arg), null);
 
     // Then Result Is True
     assertTrue(result);
   }
 
-  @Test
-  void whenCallingIsValidOnLocaleWithUnknownKeyThenResultIsFalse() {
+  @ParameterizedTest
+  @ValueSource(strings = {"unknown", "a12345678", "123456789", "12345678", "1234567"})
+  void whenCallingIsValidOnLocaleWithInvalidLanguageThenResultIsFalse(String arg) {
 
-    // When Calling Is Valid On Locale With Unknown Key
-    final var result = validator.isValid(new Locale("unknown"), null);
+    // When Calling Is Valid On Locale With Invalid Language
+    final var result = validator.isValid(new Locale(arg), null);
 
     // Then Result Is False
     assertFalse(result);