How to embed Unicode fonts in EPUB ebooks

I own a Barnes and Noble's Nook and recently had a trouble reading a Vietnamese novel on Nook. But I resolved the issue by hacking the EPUB ebook as explained below:

1. Get the Unicode fonts that you want for your ebook. The following fonts come with Adobe Reader and cover enough Unicode ranges.
   
   • MyriadPro-Bold.otf
     
   • MyriadPro-It.otf
     
   • MyriadPro-Regular.otf
   
   With 7-zip, put the Unicode fonts in your ebook.
   
2. Extract content.opf from your ebook and insert the following lines in the manifest section:
   

   <item href="MyriadPro-Bold.otf" id="embedded.font.bold" media-type="font/opentype"/>
   
   <item href="MyriadPro-It.otf" id="embedded.font.italic" media-type="font/opentype"/>
   
   <item href="MyriadPro-Regular.otf" id="embedded.font.regular" media-type="font/opentype"/>
   

   Put content.opt back into the ebook file.
   
3. Extract stylesheet.css from the ebook and append the following contents:
   

   @font-face {
   font-family: "Myriad Pro";
   font-weight: normal;
   font-style: normal;
   src: url(MyriadPro-Regular.otf);
   }
   @font-face {
   font-family: "Myriad Pro";
   font-weight: normal;
   font-style: italic;
   src: url(MyriadPro-It.otf);
   }
   @font-face {
   font-family: "Myriad Pro";
   font-weight: bold;
   font-style: normal;
   src: url(MyriadPro-Bold.otf);
   }
   a {
       color: inherit;
       text-decoration: inherit;
       }
   em, i {
   font-family: "Myriad Pro", sans-serif;
   font-weight: normal;
   font-style: italic;
   }
   strong, b, h1, h2, h3, h4, h5 {
   font-family: "Myriad Pro", sans-serif;
   font-weight: bold;
   font-style: normal;
   }
   body {
   font-family: "Myriad Pro", sans-serif;
       margin-left: 5pt;
       margin-right: 5pt;
       text-align: justify;
   }
   p {
     text-indent: 2em;
     margin-top: 0pt;
     margin-bottom: 0pt;
     }
   

   Put stylesheet back in your ebook.
   
4. Try and read your ebook with Adobe Digital Editions or your favorite ebook reader.