Fixed issue with loading messages in different language. As a standalone jar you can write properties back to messages.properties, this approach worked when you run with exploded classpath (target/classes etc). However failed when running inside Docker container.

webgoat-container/src/main/java/org/owasp/webgoat/i18n/Messages.java

@@ -46,6 +46,7 @@ public class Messages extends ReloadableResourceBundleMessageSource {
 
     /**
      * Gets all messages for presented Locale.
+     *
      * @return all messages
      */
     public Properties getMessages() {
@@ -64,4 +65,6 @@ public class Messages extends ReloadableResourceBundleMessageSource {
         return localeResolver.resolveLocale(((ServletRequestAttributes) RequestContextHolder.currentRequestAttributes()).getRequest());
     }
 
+
+
 }

webgoat-container/src/main/java/org/owasp/webgoat/i18n/PluginMessages.java

@@ -0,0 +1,80 @@
+/*
+ * This file is part of WebGoat, an Open Web Application Security Project utility. For details,
+ * please see http://www.owasp.org/
+ * <p>
+ * Copyright (c) 2002 - 2017 Bruce Mayhew
+ * <p>
+ * This program is free software; you can redistribute it and/or modify it under the terms of the
+ * GNU General Public License as published by the Free Software Foundation; either version 2 of the
+ * License, or (at your option) any later version.
+ * <p>
+ * This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without
+ * even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
+ * General Public License for more details.
+ * <p>
+ * You should have received a copy of the GNU General Public License along with this program; if
+ * not, write to the Free Software Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA
+ * 02111-1307, USA.
+ * <p>
+ * Getting Source ==============
+ * <p>
+ * Source for this application is maintained at https://github.com/WebGoat/WebGoat, a repository for free software
+ * projects.
+ * <p>
+ */
+
+package org.owasp.webgoat.i18n;
+
+import lombok.SneakyThrows;
+import org.springframework.context.support.ReloadableResourceBundleMessageSource;
+import org.springframework.core.io.Resource;
+import org.springframework.core.io.ResourceLoader;
+import org.springframework.core.io.UrlResource;
+
+import java.io.File;
+import java.util.Properties;
+
+/**
+ * Message resource bundle for plugins. The files is created after startup during the init of the plugins so we
+ * need to load this file through a ResourceLoader instead of location on the classpath.
+ *
+ * @author nbaars
+ * @date 2/4/17
+ */
+public class PluginMessages extends ReloadableResourceBundleMessageSource {
+
+    private Messages messages;
+
+    public PluginMessages(Messages messages) {
+        this.messages = messages;
+        this.setParentMessageSource(messages);
+    }
+
+    public Properties getMessages() {
+        return getMergedProperties(messages.resolveLocale()).getProperties();
+    }
+
+    public String getMessage(String code, Object... args) {
+        return getMessage(code, args, messages.resolveLocale());
+    }
+
+    public String getMessage(String code, String defaultValue, Object... args) {
+        return super.getMessage(code, args, defaultValue, messages.resolveLocale());
+    }
+
+    public void addPluginMessageBundles(final File i18nPluginDirectory) {
+        this.setBasename("WebGoatLabels");
+        this.setResourceLoader(new ResourceLoader() {
+            @Override
+            @SneakyThrows
+            public Resource getResource(String location) {
+                return new UrlResource(new File(i18nPluginDirectory, location).toURI());
+            }
+
+            @Override
+            public ClassLoader getClassLoader() {
+                return Thread.currentThread().getContextClassLoader();
+            }
+        });
+    }
+}