How to determine the message status (read/unread) in chat?

How to determine the message status (read/unread). Chat is realized with the XMPP protocol.

When you unread a message does it still say seen?

Mark unread will only take effect on your end. This helps you know that the message is new and needs viewing. But the sender will still see that you have already read the message.

When you mark as unread on WhatsApp does it still say seen?

It is vital to note here that marking a message as 'unread' only means that your messages are marked unread only for you. The sender will continue seeing the Blue Ticks indicating that you have read the messages but not replied.

XEP-0184: Message Delivery Receipts supports notifying senders when their message has been delivered. You might be able to use that as a building block, as long as you don't expect existing clients to send these receipts -- the XEP is not widely-implemented today.