Localization (often abbreviated as l10n) and internationalization (often abbreviated as i18n) "are means of adapting computer software to different languages, regional peculiarities and technical requirements of a target locale." – Wikipedia:Internationalization and localization
Subpages listed below contain instructions on localization of your system to specific languages:
See Fonts#Non-latin scripts for a non-exhaustive list of available non-Latin fonts.
See Locale for help with adding non-Latin language support to your system.
See Input method for help with non-Latin text input.
See Keyboard configuration in console and Keyboard configuration in Xorg.