install_check_translation_download in core/includes/install.core.inc

Checks installation requirements, downloads a translation, and reports any errors.

install_get_available_translations in core/includes/install.core.inc

Provide a list of available translation files.

install_import_translations in core/includes/install.core.inc

Imports languages via a batch process during installation.

language_admin_add_predefined_form_submit in core/modules/language/language.admin.inc

Process the predefined language addition form submission.

language_admin_predefined_list in core/modules/language/language.admin.inc

Prepare a language code list for unused predefined languages.

language_save in core/modules/language/language.module

API function to add or update a language.

language_update_1003 in core/modules/language/language.install

Add the native name to all enabled languages.

locale_translate_import_form_submit in core/modules/locale/locale.bulk.inc

Process the locale import form submission.