diff --git a/src/main/java/net/hostsharing/hsadminng/credentials/HsCredentialsController.java b/src/main/java/net/hostsharing/hsadminng/credentials/HsCredentialsController.java
index b91914e3..fef10830 100644
--- a/src/main/java/net/hostsharing/hsadminng/credentials/HsCredentialsController.java
+++ b/src/main/java/net/hostsharing/hsadminng/credentials/HsCredentialsController.java
@@ -5,6 +5,7 @@ import java.util.UUID;
 
 import io.micrometer.core.annotation.Timed;
 import io.swagger.v3.oas.annotations.security.SecurityRequirement;
+import net.hostsharing.hsadminng.config.MessageTranslator;
 import net.hostsharing.hsadminng.context.Context;
 import net.hostsharing.hsadminng.credentials.generated.api.v1.api.CredentialsApi;
 import net.hostsharing.hsadminng.credentials.generated.api.v1.model.CredentialsInsertResource;
@@ -17,6 +18,8 @@ import org.springframework.beans.factory.annotation.Autowired;
 import org.springframework.http.ResponseEntity;
 import org.springframework.web.bind.annotation.RestController;
 
+import jakarta.persistence.EntityNotFoundException;
+
 @RestController
 @SecurityRequirement(name = "casTicket")
 public class HsCredentialsController implements CredentialsApi {
@@ -30,6 +33,9 @@ public class HsCredentialsController implements CredentialsApi {
     @Autowired
     private StrictMapper mapper;
 
+    @Autowired
+    private MessageTranslator messageTranslator;
+
     @Autowired
     private HsOfficePersonRbacRepository personRepo;
 
@@ -56,7 +62,12 @@ public class HsCredentialsController implements CredentialsApi {
     ) {
         context.assumeRoles(assumedRoles);
 
-        final var person = personRepo.findByUuid(personUuid).orElseThrow(); // FIXME: use proper exception
+        final var person = personRepo.findByUuid(personUuid).orElseThrow(
+                () -> new EntityNotFoundException(
+                        messageTranslator.translate("{0} \"{1}\" not found or not accessible", "personUuid", personUuid)
+                )
+
+        ); // FIXME: use proper exception
         final var credentials = credentialsRepo.findByPerson(person);
         final var result = mapper.mapList(credentials, CredentialsResource.class);
         return ResponseEntity.ok(result);
@@ -96,7 +107,7 @@ public class HsCredentialsController implements CredentialsApi {
 
         final var current = credentialsRepo.findByUuid(credentialsUuid).orElseThrow();
 
-        new HsCredentialsEntityPatcher(em, current).apply(body);
+        new HsCredentialsEntityPatcher(em, messageTranslator, current).apply(body);
 
         final var saved = credentialsRepo.save(current);
         final var mapped = mapper.map(saved, CredentialsResource.class);
diff --git a/src/main/java/net/hostsharing/hsadminng/credentials/HsCredentialsEntityPatcher.java b/src/main/java/net/hostsharing/hsadminng/credentials/HsCredentialsEntityPatcher.java
index 164fcc12..44f1ccd2 100644
--- a/src/main/java/net/hostsharing/hsadminng/credentials/HsCredentialsEntityPatcher.java
+++ b/src/main/java/net/hostsharing/hsadminng/credentials/HsCredentialsEntityPatcher.java
@@ -1,5 +1,6 @@
 package net.hostsharing.hsadminng.credentials;
 
+import net.hostsharing.hsadminng.config.MessageTranslator;
 import net.hostsharing.hsadminng.credentials.generated.api.v1.model.ContextResource;
 import net.hostsharing.hsadminng.credentials.generated.api.v1.model.CredentialsPatchResource;
 import net.hostsharing.hsadminng.mapper.EntityPatcher;
@@ -14,10 +15,12 @@ import java.util.stream.Collectors;
 public class HsCredentialsEntityPatcher implements EntityPatcher<CredentialsPatchResource> {
 
     private final EntityManager em;
+    private MessageTranslator messageTranslator;
     private final HsCredentialsEntity entity;
 
-    public HsCredentialsEntityPatcher(final EntityManager em, final HsCredentialsEntity entity) {
+    public HsCredentialsEntityPatcher(final EntityManager em, MessageTranslator messageTranslator, final HsCredentialsEntity entity) {
         this.em = em;
+        this.messageTranslator = messageTranslator;
         this.entity = entity;
     }
 
@@ -57,14 +60,15 @@ public class HsCredentialsEntityPatcher implements EntityPatcher<CredentialsPatc
             if (!entityUuids.contains(resource.getUuid())) {
                 final var existingContextEntity = em.find(HsCredentialsContextRealEntity.class, resource.getUuid());
                 if ( existingContextEntity == null ) {
-                    // FIXME: i18n
                     throw new EntityNotFoundException(
-                            HsCredentialsContextRealEntity.class.getName() + " with uuid " + resource.getUuid() + " not found.");
+                            messageTranslator.translate("{0} \"{1}\" not found or not accessible",
+                                    "credentials uuid", resource.getUuid()));
                 }
                 if (!existingContextEntity.getType().equals(resource.getType()) &&
                     !existingContextEntity.getQualifier().equals(resource.getQualifier())) {
-                    // FIXME: i18n
-                    throw new EntityNotFoundException("existing " +  existingContextEntity + " does not match given resource " + resource);
+                    throw new EntityNotFoundException(
+                            messageTranslator.translate("existing {0} does not match given resource {1}",
+                                    existingContextEntity, resource));
                 }
                 entities.add(existingContextEntity);
             }
diff --git a/src/main/resources/i18n/messages_de.properties b/src/main/resources/i18n/messages_de.properties
index 01da06ad..5494037e 100644
--- a/src/main/resources/i18n/messages_de.properties
+++ b/src/main/resources/i18n/messages_de.properties
@@ -12,6 +12,9 @@ unknown\ authorization\ ticket=unbekanntes Autorisierungs-Ticket
 {0}\ "{1}"\ not\ found\ or\ not\ accessible={0} "{1}" nicht gefunden oder nicht zugänglich
 but\ is=ist aber
 
+# credentials validations
+existing\ {0}\ does\ not\ match\ given\ resource\ {1}=existierender Credentials-Context {0} passt nicht zum angegebenen {1}
+
 # office.coop-shares
 for\ transactionType\={0},\ shareCount\ must\ be\ positive\ but\ is\ {1}=für transactionType={0}, muss shareCount positiv sein, ist aber {1}
 for\ transactionType\={0},\ shareCount\ must\ be\ negative\ but\ is\ {1}=für transactionType={0}, muss shareCount negativ sein, ist aber {1}
diff --git a/src/test/java/net/hostsharing/hsadminng/credentials/HsCredentialsEntityPatcherUnitTest.java b/src/test/java/net/hostsharing/hsadminng/credentials/HsCredentialsEntityPatcherUnitTest.java
index 4041a302..e86171fc 100644
--- a/src/test/java/net/hostsharing/hsadminng/credentials/HsCredentialsEntityPatcherUnitTest.java
+++ b/src/test/java/net/hostsharing/hsadminng/credentials/HsCredentialsEntityPatcherUnitTest.java
@@ -1,5 +1,6 @@
 package net.hostsharing.hsadminng.credentials;
 
+import net.hostsharing.hsadminng.config.MessageTranslator;
 import net.hostsharing.hsadminng.credentials.generated.api.v1.model.ContextResource;
 import net.hostsharing.hsadminng.credentials.generated.api.v1.model.CredentialsPatchResource;
 import net.hostsharing.hsadminng.rbac.test.PatchUnitTestBase;
@@ -19,6 +20,7 @@ import java.util.stream.Stream;
 import static org.junit.jupiter.api.TestInstance.Lifecycle.PER_CLASS;
 import static org.mockito.ArgumentMatchers.eq;
 import static org.mockito.Mockito.lenient;
+import static org.mockito.Mockito.mock;
 
 @TestInstance(PER_CLASS)
 @ExtendWith(MockitoExtension.class)
@@ -115,7 +117,7 @@ class HsCredentialsEntityPatcherUnitTest extends PatchUnitTestBase<
 
     @Override
     protected HsCredentialsEntityPatcher createPatcher(final HsCredentialsEntity entity) {
-        return new HsCredentialsEntityPatcher(em, entity);
+        return new HsCredentialsEntityPatcher(em, mock(MessageTranslator.class), entity);
     }
 
     @Override