Answering your questions:
- Windows version: Windows XP SP3 (English);
- Do you have "Tahoma" and "Arial Unicode MS" fonts installed? : Both "Tahoma" and "Arial Unicode MS" fonts are installed;
- Can these fonts display Georgian characters (in the same Notepad)? : Yes, all Unicode supporting applications can display Georgian characters, using both of the mentioned fonts;
- Does your browser correctly display JIRA pages with national characters when configured to use auto-detection? : Yes, all browsers do display characters correctly.
Besides, this is not an issue on one computer, but on several.
Thank you for your prompt reply.
QUOTE (Igor Sereda @ December 28, 2010)

Hello, thanks for posting the screenshot!
There are two possible reasons for this problem: a) the font used by the application cannot display the characters correctly (but the characters themselves are fine);

the characters are incorrectly read from JIRA.
To check the first version, could you please tell,
- What's your Windows version?
- Do you have "Tahoma" and "Arial Unicode MS" fonts installed? (You can tell, for example, by running Notepad and selecting font with Format | Font menu.)
- Can these fonts display Georgian characters (in the same Notepad)?
To check the second version, does your browser correctly display JIRA pages with national characters when configured to use auto-detection? (For example, in Internet Explorer, menu Page | Encoding | Auto-Select.)
Thanks!
Kind regards,
Igor