http://en.wikipedia.org/wiki/I18n:

Internationalization is often abbreviated as I18N (or i18n or I18n), by IBM and others, where the number 18 refers to the number of letters omitted. "Localization" is often abbreviated L10n or l10n in the same manner. (The most common forms are i18n and L10n, respectively. These forms won out because many fonts do not readily distinguish uppercase "I" and lowercase "l", but lowercase "i" and uppercase "L" are always clear.) Both notions are sometimes collectively termed globalization (g11n), but that word has a more common meaning. Also seen in some circles, but less commonly, are "p13n" for personalization, "m17n" for multilingualization, and "r3h" for reach, as in the reach of a website across countries and markets.