Can not use Vietnamese font on Openfire 3.10.3 and Spark 2.7.4

Hi, all

I am a beginner on using Spark chat. I am from Vietnam.

I am deploying Chat system using Open fire 3.10.3, Spark 2.7.4 and XAMPP (MySQL server).

My system is working normally when users chatting online. The problem is when they send offline messages, the receiver can not read these messages because of missing Vietnamese font.

I think the problem is when sender send offline message, these massage will be stored on Database (MySQL). The Database configurations has changed these offline messages but I do not know how to fix it.

Please, help me to fix this issue

Thank you very much