The site font seems to be Arial, or Helvetica, at least something similar. It has good support for Cyrillic, Greek letters. However, I noticed this font is incompatible with some scripts, e.g. Chinese, Japanese, Korean. When you are using firefox, the site uses Song (default Chinese font for ff, a serif font) to display Chinese pages, and the outcome is rather weird, like a mixture of Song and Square sans.

The most widely used "sans serif" fonts for CJK:
Chinese: Microsoft YaHei (微软雅黑, windows) or STXihei (华文细黑, Mac OS)
Japanese, it is Meiryo (メイリオ) or Hiragino Kaku Gothic (Mac OS X)
Korean, Malgun Gothic (맑은 고딕, for windows) or AppleGothic (Mac OS X).

Also the default font is a little strange when displaying Romanian ș (s-comma).

I suggest the webmaster consider setting up the default fonts for different languages.

I will try to compile the info about the fonts of other scripts.

That'd mean detecting the language of each string, and displaying different CSS for these strings every time...? Hell no. Sorry, but it's just not practical.