Show toast warning for duplicate attachments

app/src/main/res/values-zh-rCN/strings.xml

@@ -20,6 +20,8 @@
     <string name="unpin_conversation">取消固定</string>
     <string name="forward_message">转发</string>
     <string name="compress_error">无法将图像压缩到选定的大小</string>
+    <!-- Attachments-->
+    <string name="duplicate_item_warning">Duplicate item was not included</string>
     <!-- vCard-->
     <plurals name="and_other_contacts">
         <item quantity="other">及 %d 个其他人</item>
@@ -84,4 +86,4 @@
         Haven't found some strings? There's more at
         https://github.com/SimpleMobileTools/Simple-Commons/tree/master/commons/src/main/res
     -->
-</resources>
+</resources>