i18n means Internationalization, where 18 stands for the number of letters in word Internationalization between the first i and last n. It is the process of developing products in such a way that they can be localized for languages and cultures easily.

L10n means Localization, where 10 stand for the number of letters in word Localization between the first L and last n. It is the process of adapting applications and text to enable their usability in a particular culture.