The following Unicode fonts include characters in (almost) every language and are useful when you need are using a deck published by someone else on the Internet for which you do not have the correct font. They are currently free.
TITUS Cyberbit Basic ---- a very fast download and one of the most useful fonts you could ask for. This compact font contains a large part of the UNICODE character set (Latin, Chinese, Japanese etc), and it's free! This is a very useful font to include in web pages if you think that the average person will not have the right fonts installed on their computer to view the cards that you create.
Microsoft's Arial Unicode ---- a very memory-intensive font, but a nicer looking font than TITUS Cyberbit Basic. Although you can no longer download this font, it is included with Windows XP and Microsoft Publisher.
Gentium
font does not offer as many language variations as TITUS but it
is a much nicer looking font. I include the author, Victor Gaultney's,
description from his homepage:
"Gentium is a typeface family designed to enable the diverse
ethnic groups around the world who use the Latin script to produce
readable, high-quality publications. It supports a wide range
of Latin-based alphabets and includes glyphs that correspond to
all the Latin ranges of Unicode.
The design is intended to be highly readable, reasonably compact, and visually attractive. The additional 'extended' Latin letters are designed to naturally harmonize with the traditional 26 ones. Diacritics are treated with careful thought and attention to their use. Gentium also supports both ancient and modern Greek, including a number of alternate forms."