Or if you want to give a gloss, 'the problem of gaiji (non-standard characters)'.

The Gaiji problem

Japanese DTP is 10 years old, yet, despite all of Apple's and Adobe's growth here, the penetration rate is less than 50 percent. There are many reasons for this, but one of the most important is the font problem and the lack of gaiji. Gaiji are Kanji characters outside of the current JIS (Japanese Industrial Standard) and Unicode encoding sets and are not included in a standard font. This is one reason why publishers hang on to proprietary systems.
http://www.macintouch.com/gaiji.html

Gaiji (外字), literally meaning "external characters," are kanji that are not represented in existing Japanese encoding systems. These include variant forms of common kanji that need to be represented alongside the more conventional glyph in reference works, and can include non-kanji symbols as well.

Gaiji can be either user-defined characters or system-specific characters. Both are a problem for information interchange, as the codepoint used to represent an external character will not be consistent from one computer or operating system to another.
http://www.newworldencyclopedia.org/entry/Kanji