For questions related to making an extension support many languages, adding translation strings, creating language overrides etc. * For questions related in creating Joomla sites with multi-lingual content, better use the multilingual tag.
Joomla and many extensions are shipped in various languages. To support this functionality, language packs can be installed for Joomla, while extensions can contain many language files. A language file is a special php.ini file dedicated to a specific language, that contains the languages strings used across the extension and their translations for that language.