There are numerous obstacles to having multilingual email over the Internet which include:
1. The email application
2. Requirements for fonts or language kits to be installed
3. Gateways
4. The need for Unicode, 32-bit file systems
Here's why:
1) The e-mail application
With the possible exception of CyberDog, we are not aware of an Internet email program that is 2-byte font aware. A "closed" system (without Internet access) like QuickMail, may work properly if other requirements like fonts, language kits, gateways, and so on are met.
2) Requirements for fonts or language kits to be installed
The correct font is required to view the associated glyphs or characters. As an example, if the receiving font is missing a glyph (for instance, a "y"), then the word might appear "gl_ph" with a square (control character) or other character, based on various character mapping possibilities. Since different platforms map their fonts differently, another level of complexity gets added. Additionally, a secondary language script associated with a language kit like JLK may also be required. There's also setting a font like Osaka for JLK (in the Views control panel), so 2-byte filenames and folder names can be used by the Finder. For anyone who has used the Apple Language Kits, this should already be clear.
3) Gateways (This term means any intervening steps through which an email message passes--not the strict network definition.)
On a recent email test from Japan that we received, the KanjiTalk examples were corrupted by intervening gateways.
4) The need for Unicode 32-bit filesystems, which would (theoretically) support any font in filename space, and eventually across all major platforms.
The Mac OS today, as well as DOS/Windows, NeXTStep, OpenStep, and others may use 7-bit filesystems (with some variances). So the answer, ultimately, is to have files and directories on all platforms map to a common Unicode 32-bit name space which would allow for names to appear properly.