error subtitle !vietnamese

Hi everybody!
My subtitle language is Vietnamese, and sometimes it does not display the letter or letters lost, broken words. I think it’s because of XBMC font is not fully supported. So the solution is to install fonts in kodi (arialuni.ttf)
 
You how to install or add a font to kodi.
I used openelec on cubox ipro4. Set via SFTP or any way.
Anyone who knows this, can help me?
I am very grateful!