This document discusses internationalization and localization for WordPress themes. It explains that internationalization (i18n) is the process of making a theme translatable by wrapping strings in translation functions like _e() and __(). Localization (l10n) is the actual translation of strings into other languages. It provides tips for internationalization including using text domains, supporting right-to-left languages, and handling language files like .pot, .po and .mo files. Tools for generating and managing translations are also mentioned.