diff --git a/WEBSERVICES/ZUGFeRDRESTService/Controllers/ValidationController.cs b/WEBSERVICES/ZUGFeRDRESTService/Controllers/ValidationController.cs
index b629122b..c7029f79 100644
--- a/WEBSERVICES/ZUGFeRDRESTService/Controllers/ValidationController.cs
+++ b/WEBSERVICES/ZUGFeRDRESTService/Controllers/ValidationController.cs
@@ -1,6 +1,7 @@
 using DigitalData.Modules.Interfaces;
 using Microsoft.AspNetCore.Http;
 using Microsoft.AspNetCore.Mvc;
+using Microsoft.CodeAnalysis.CSharp.Syntax;
 using Microsoft.Extensions.Configuration;
 using System;
 using System.Collections.Generic;
@@ -47,7 +48,14 @@ namespace ZUGFeRDRESTService.Controllers
         public const string REFERENCES_Rejection_30012 = "REFERENCES_Rejection_30012";
         public const string AMOUNT_CALC_REJECTION = "AMOUNT_CALC_REJECTION";
 
+        public const string GERMAN = "de-DE";
+        public const string ENGLISH = "en-US";
+        public const string FRENCH = "fr-FR";
+        public const string SPAIN = "es-ES";
+
         private List<string> _ValidationErrors;
+        private List<string> _AllowedLanguageCodes;
+        private string _UserLanguageCode = "de-DE";
 
         private const int MAX_FILE_SIZE_DEFAULT = 25;
 
@@ -128,6 +136,14 @@ namespace ZUGFeRDRESTService.Controllers
                 AMOUNT_CALC_REJECTION
             };
 
+            _AllowedLanguageCodes = new List<string>()
+            {
+                GERMAN,
+                ENGLISH,
+                FRENCH,
+                SPAIN,
+            };
+
             _logger.Debug("Validation Controller initialized!");
         }
 
@@ -191,14 +207,41 @@ namespace ZUGFeRDRESTService.Controllers
         /// </summary>
         /// <param name="file">This parameter's name needs to correspond to the html form's file-input name</param>
         /// <param name="user_id">This is the email address which the user supplied</param>
+        /// <param name="language_id">This is language code which the user supplied (en-US, de-DE)</param>
         [HttpPost]
-        public ValidationResponse Post(IFormFile file, string user_id)
+        public ValidationResponse Post(IFormFile file, string user_id, string language_id = null)
         {
             _logger.Info("Start processing request to ValidationController");
 
             ZugferdResult oZugferdResult = null;
             CheckPropertyValuesResult oPropertyResult = new CheckPropertyValuesResult();
 
+            if (!string.IsNullOrEmpty(user_id))
+            {
+                _logger.Info("UserID set to [{0}].", user_id);
+            } 
+            else
+            {
+                _logger.Info("UserID is empty!");
+            }
+
+            if (string.IsNullOrEmpty(language_id))
+            {
+                _logger.Info("Language code was empty. Set to default 'de-DE'");
+                // DEFAULT-Sprache = Deutsch de-DE
+                _UserLanguageCode = GERMAN;
+            }
+            else if (_AllowedLanguageCodes.Contains(language_id))
+            {
+                _logger.Info("Language code is allowed. Set to [{0}].", language_id);
+                _UserLanguageCode = language_id;
+            }
+            else
+            {
+                _logger.Info("Language code was unknown: [{0}]. Set to default 'de-DE'", language_id);
+                _UserLanguageCode = GERMAN;
+            }
+
             try
             {
                 using Stream oStream = file.OpenReadStream();
@@ -299,7 +342,7 @@ namespace ZUGFeRDRESTService.Controllers
                         };
                     }
                 }
-                
+
             }
             catch (ZUGFeRDExecption ex)
             {
@@ -611,7 +654,7 @@ namespace ZUGFeRDRESTService.Controllers
             return oReplaceParam1;
         }
 
-        public string GetMessageId()
+        private string GetMessageId()
         {
             return $"{Guid.NewGuid()}@{MESSAGEID_DOMAIN}";
         }
@@ -772,7 +815,7 @@ namespace ZUGFeRDRESTService.Controllers
             return oDataTable;
         }
 
-        public bool DeleteExistingPropertyValues(string pMessageId)
+        private bool DeleteExistingPropertyValues(string pMessageId)
         {
             try
             {
@@ -816,18 +859,15 @@ namespace ZUGFeRDRESTService.Controllers
             return true;
         }
 
-        
         /// <summary>
         /// Ermittelt die Ausgabe-nachricht für einen Fehlercode 
         /// </summary>
-        public string GetRejectionMessage(string pErrorCode)
+        private string GetRejectionMessage(string pErrorCode)
         {
             _logger.Info("GetRejectionMessage() - errorCode.ToString(): '" + pErrorCode.ToString() + "'");
 
             if (_RecjectionMessageList == null) return string.Empty;
 
-            // Sprache wird man vielleicht mal auswählen können
-            var language = "de-DE";
             var searchTitle = string.Empty;
 
             if (pErrorCode.Contains("2000"))
@@ -844,11 +884,23 @@ namespace ZUGFeRDRESTService.Controllers
             }
             else
             {
-                // else-Fall muss noch geklärt werden.
-                searchTitle = "AMOUNT_CALC_REJECTION_Web";
+                searchTitle = "ZUGFERD_Rejection_20006_Web";
+            }
+
+            // Sprachgenauen Text suchen.
+            var messageItem = _RecjectionMessageList.Where(i => i.Title.Equals(searchTitle, StringComparison.OrdinalIgnoreCase) &&
+                                                                i.Language.Equals(_UserLanguageCode, StringComparison.OrdinalIgnoreCase)).FirstOrDefault();
+
+            if (messageItem == null && 
+                !_UserLanguageCode.Equals(GERMAN, StringComparison.OrdinalIgnoreCase)) {
+
+                _logger.Info("GetRejectionMessage() - Es wurde kein passender Text für die Sprache [{0}] gefunden.", _UserLanguageCode);
+
+                // Wenn kein sprachgenauer Text vorliegt, hole den deutschen Text.
+                messageItem = _RecjectionMessageList.Where(i => i.Title.Equals(searchTitle, StringComparison.OrdinalIgnoreCase) &&
+                                                                i.Language.Equals(GERMAN, StringComparison.OrdinalIgnoreCase)).FirstOrDefault();
             }
 
-            var messageItem = _RecjectionMessageList.Where(i => i.Title.Equals(searchTitle, StringComparison.OrdinalIgnoreCase) && i.Language.Equals(language, StringComparison.OrdinalIgnoreCase)).FirstOrDefault();
             if (messageItem != null)
             {
                 _logger.Info("GetRejectionMessage() - messageItem: '" + messageItem.String1 + "'");
diff --git a/WEBSERVICES/ZUGFeRDRESTService/Pages/Index.cshtml b/WEBSERVICES/ZUGFeRDRESTService/Pages/Index.cshtml
index d941e9ef..1b7cf371 100644
--- a/WEBSERVICES/ZUGFeRDRESTService/Pages/Index.cshtml
+++ b/WEBSERVICES/ZUGFeRDRESTService/Pages/Index.cshtml
@@ -15,7 +15,12 @@
         <label>Benutzerkennung/Email:</label>
         <input type="email" name="user_id" required />
     </p>
-    
+
+    <p>
+        <label>Sprachcode (de-DE etc.):</label>
+        <input type="text" name="language_id" value="de-DE" required />
+    </p>
+
     <button type="submit">Submit</button>
 </form>