The Interface translation module is responsible for providing an interface that allows users to translate any string or text output on the website, in all the languages that are installed. Moreover, it provides a connection to the localize.drupal.org platform from which it can download translations for many languages of the more common interface strings that come with Drupal:
These four modules are not alone in the multilingual system but rely on a cross-application standard of ensuring that all the written code works well with it. In other words, the entire Drupal code base is intertwined with the multilingual system at various levels, and is written in such a way that anything that should be translatable or localizable can be. This means that all the code we write needs to respect the same standard.