diff --git a/com.avaloq.tools.ddk.checkcfg.core.test/src/com/avaloq/tools/ddk/checkcfg/validation/CheckCfgTest.java b/com.avaloq.tools.ddk.checkcfg.core.test/src/com/avaloq/tools/ddk/checkcfg/validation/CheckCfgTest.java
index dbad41e80..96c982960 100644
--- a/com.avaloq.tools.ddk.checkcfg.core.test/src/com/avaloq/tools/ddk/checkcfg/validation/CheckCfgTest.java
+++ b/com.avaloq.tools.ddk.checkcfg.core.test/src/com/avaloq/tools/ddk/checkcfg/validation/CheckCfgTest.java
@@ -58,4 +58,21 @@ public void testUnknownLanguageNotOk() throws Exception {
     helper.assertError(model, CheckcfgPackage.Literals.CONFIGURED_LANGUAGE_VALIDATOR, IssueCodes.UNKNOWN_LANGUAGE);
   }
 
+  @Test
+  public void testDuplicateLanguageNotOk() throws Exception {
+    final CheckConfiguration model = parser.parse("""
+        check configuration Test
+
+        for com.avaloq.tools.ddk.^check.TestLanguage {
+
+        }
+
+        for com.avaloq.tools.ddk.^check.TestLanguage {
+
+        }
+
+        """);
+    helper.assertError(model, CheckcfgPackage.Literals.CONFIGURED_LANGUAGE_VALIDATOR, IssueCodes.DUPLICATE_LANGUAGE_CONFIGURATION);
+  }
+
 }
diff --git a/com.avaloq.tools.ddk.checkcfg.core/src/com/avaloq/tools/ddk/checkcfg/validation/CheckCfgValidator.java b/com.avaloq.tools.ddk.checkcfg.core/src/com/avaloq/tools/ddk/checkcfg/validation/CheckCfgValidator.java
index 61a1b61f3..f65d12c8f 100644
--- a/com.avaloq.tools.ddk.checkcfg.core/src/com/avaloq/tools/ddk/checkcfg/validation/CheckCfgValidator.java
+++ b/com.avaloq.tools.ddk.checkcfg.core/src/com/avaloq/tools/ddk/checkcfg/validation/CheckCfgValidator.java
@@ -313,6 +313,36 @@ public void checkConfiguredLanguageExists(final ConfiguredLanguageValidator vali
     }
   }
 
+  /**
+   * Checks that within a Check Configuration all Configured Language Validators are unique, meaning that
+   * the same language can only be configured in one place.
+   *
+   * @param configuration
+   *          the configuration
+   */
+  @Check
+  public void checkConfiguredLanguageUnique(final CheckConfiguration configuration) {
+    if (configuration.getLanguageValidatorConfigurations().size() < 2) {
+      return;
+    }
+    Predicate<ConfiguredLanguageValidator> predicate = new Predicate<ConfiguredLanguageValidator>() {
+      @Override
+      public boolean apply(final ConfiguredLanguageValidator validator) {
+        return validator.getLanguage() != null;
+      }
+    };
+    Function<ConfiguredLanguageValidator, String> function = new Function<ConfiguredLanguageValidator, String>() {
+      @Override
+      public String apply(final ConfiguredLanguageValidator from) {
+        return from.getLanguage();
+      }
+    };
+    for (final ConfiguredLanguageValidator v : getDuplicates(predicate, function, configuration.getLanguageValidatorConfigurations())) {
+      error(Messages.CheckCfgJavaValidator_DUPLICATE_LANGUAGE_CONFIGURATION, v, CheckcfgPackage.Literals.CONFIGURED_LANGUAGE_VALIDATOR__LANGUAGE, ValidationMessageAcceptor.INSIGNIFICANT_INDEX, IssueCodes.DUPLICATE_LANGUAGE_CONFIGURATION);
+    }
+
+  }
+
   /**
    * Checks that a Configured Check has unique Configured Parameters.
    *
diff --git a/com.avaloq.tools.ddk.checkcfg.core/src/com/avaloq/tools/ddk/checkcfg/validation/IssueCodes.java b/com.avaloq.tools.ddk.checkcfg.core/src/com/avaloq/tools/ddk/checkcfg/validation/IssueCodes.java
index 2a9818854..75ae4c479 100644
--- a/com.avaloq.tools.ddk.checkcfg.core/src/com/avaloq/tools/ddk/checkcfg/validation/IssueCodes.java
+++ b/com.avaloq.tools.ddk.checkcfg.core/src/com/avaloq/tools/ddk/checkcfg/validation/IssueCodes.java
@@ -26,6 +26,7 @@ public final class IssueCodes {
   public static final String DUPLICATE_CATALOG_CONFIGURATION = ISSUE_CODE_PREFIX + "duplicate_catalog_configuration";
   public static final String DUPLICATE_CHECK_CONFIGURATION = ISSUE_CODE_PREFIX + "duplicate_check_configuration";
   public static final String UNKNOWN_LANGUAGE = ISSUE_CODE_PREFIX + "unknown_language";
+  public static final String DUPLICATE_LANGUAGE_CONFIGURATION = ISSUE_CODE_PREFIX + "duplicate_language_configuration";
   public static final String DUPLICATE_PARAMETER_CONFIGURATION = ISSUE_CODE_PREFIX + "duplicate_parameter_configuration";
   public static final String SEVERITY_NOT_ALLOWED = ISSUE_CODE_PREFIX + "severity_not_allowed";
   public static final String PARAMETER_VALUE_NOT_ALLOWED = ISSUE_CODE_PREFIX + "parameter_value_not_allowed";
diff --git a/com.avaloq.tools.ddk.checkcfg.core/src/com/avaloq/tools/ddk/checkcfg/validation/Messages.java b/com.avaloq.tools.ddk.checkcfg.core/src/com/avaloq/tools/ddk/checkcfg/validation/Messages.java
index e96bcdc20..66dfb4bb3 100644
--- a/com.avaloq.tools.ddk.checkcfg.core/src/com/avaloq/tools/ddk/checkcfg/validation/Messages.java
+++ b/com.avaloq.tools.ddk.checkcfg.core/src/com/avaloq/tools/ddk/checkcfg/validation/Messages.java
@@ -25,6 +25,7 @@ public class Messages extends NLS {
   public static String CheckCfgJavaValidator_CONFIGURED_PARAM_EQUALS_DEFAULT;
   public static String CheckCfgJavaValidator_DUPLICATE_CATALOG_CONFIGURATION;
   public static String CheckCfgJavaValidator_DUPLICATE_CHECK_CONFIGURATION;
+  public static String CheckCfgJavaValidator_DUPLICATE_LANGUAGE_CONFIGURATION;
   public static String CheckCfgJavaValidator_DUPLICATE_PARAMETER_CONFIGURATION;
   public static String CheckCfgJavaValidator_SEVERITY_NOT_ALLOWED;
 
diff --git a/com.avaloq.tools.ddk.checkcfg.core/src/com/avaloq/tools/ddk/checkcfg/validation/messages.properties b/com.avaloq.tools.ddk.checkcfg.core/src/com/avaloq/tools/ddk/checkcfg/validation/messages.properties
index 63001722a..1ad5b893d 100644
--- a/com.avaloq.tools.ddk.checkcfg.core/src/com/avaloq/tools/ddk/checkcfg/validation/messages.properties
+++ b/com.avaloq.tools.ddk.checkcfg.core/src/com/avaloq/tools/ddk/checkcfg/validation/messages.properties
@@ -5,5 +5,6 @@ CheckCfgJavaValidator_FINAL_CHECK_NOT_CONFIGURABLE=Final checks may not be confi
 CheckCfgJavaValidator_CONFIGURED_PARAM_EQUALS_DEFAULT=Configured value for ''{0}'' equals default
 CheckCfgJavaValidator_DUPLICATE_CATALOG_CONFIGURATION=Duplicate catalog configuration
 CheckCfgJavaValidator_DUPLICATE_CHECK_CONFIGURATION=Duplicate check configuration
+CheckCfgJavaValidator_DUPLICATE_LANGUAGE_CONFIGURATION=Duplicate language configuration
 CheckCfgJavaValidator_DUPLICATE_PARAMETER_CONFIGURATION=Duplicate parameter configuration
 CheckCfgJavaValidator_SEVERITY_NOT_ALLOWED=Configured severity is not allowed
\ No newline at end of file
diff --git a/com.avaloq.tools.ddk.checkcfg.ui/src/com/avaloq/tools/ddk/checkcfg/ui/quickfix/CheckCfgQuickfixProvider.java b/com.avaloq.tools.ddk.checkcfg.ui/src/com/avaloq/tools/ddk/checkcfg/ui/quickfix/CheckCfgQuickfixProvider.java
index 81495357b..387fdc43d 100644
--- a/com.avaloq.tools.ddk.checkcfg.ui/src/com/avaloq/tools/ddk/checkcfg/ui/quickfix/CheckCfgQuickfixProvider.java
+++ b/com.avaloq.tools.ddk.checkcfg.ui/src/com/avaloq/tools/ddk/checkcfg/ui/quickfix/CheckCfgQuickfixProvider.java
@@ -158,4 +158,5 @@ public void apply(final EObject element, final IModificationContext context) {
       }
     });
   }
+
 }