tuanan

glad you found the solution

yes, the code should be in style.css
I made a typo in the font name, it should be Times not Time.
I think the solution to your problem is to change the font georgia to some unicode fonts I listed above. This can be done using css or some html tags. You can find out more about hmtl and css here and here. You can choose any of these suggestions:

1. Using font tag to change the font
   Editing your post in html mode. and wrap the vietnamese content in the font tag

   This is an english sentence
   <font face="Arial">
   This sentence is in <em><font> </font></em> so the font is Times New Roman. Vietnamese text is then supported.
   </font>

   You can choose Times New Roman or Arial…

2. Using css font-family property to change font
   Changing the main font
   Insert this in your style.css

   body {font-family: Arial;}; /*change the main font to arial*/

   just replace arial with your chosen font. The main font will be changed.
   Using a css class to style the font
   add this to your style.css

   .vietnamese {font-family: Arial;}

   Then apply the class to the vietnamese content.
   Edit post in html, warp the vietnamese content in a div tag with a class of vietnamese (you could name the class anything you want)

   This is the english text
   <div class="vietnamese">
   inside this div is the vietnamese content, the font is Arial
   </div>
   orther english text

By the way, you should make sure the browser character encoding is Unicode to display Vietnamese correctly, try testing the site in other browers, other pcs, os… if the problem is not solved.

hi, tuunup, your blog is beautiful. I think the problem here is with the font used in the theme, which is Georgia. Georgia does not include the full vietnamese unicode glyphs such as “ê, ?, ?…”.
When you are editing in the wordpress admin, the font is Times New Roman, so you can see those vietnamese glyphs.
Popular vietnamese unicode fonts are Times New Roman, Arial, Tahoma, Verdana, Palatino Linotype, courier new.
The theme Vigilance with the main font georgia is great, but sadly it does not support Vietnamese language.
In this case, I would suggest editing your theme css. If you only need to use vietnamese a few times. Just add one line to your stylesheet to alter the font.

.vietnamese {font-family: "Palatino Linotype", "Time New Roman"; }

For example, if you want to use vietnamese in a paragraph, add a “vietnamese” class to it. (when editing in html, change the vietnamese paragraph to this <p class=”vietnamese”> )
Hope this helps