In Drupal 8 and later, the Translate Entity module is included in Drupal core. It manages content translations.
Translations are managed in sets of posts, which represent the same information in different languages. Only content types for which the administrator has explicitly enabled translations could have translations associated. Translations are managed in sets with exactly one source post per set. The source post is used to translate to different languages, so if the source post is significantly updated, the editor can decide to mark all translations outdated.
The node table stores the values used by this module:
tnid: Integer for the translation set ID, which equals the node ID of the source post.
translate: Integer flag, either indicating that the translation is up to date (0) or needs to be updated (1).
Functions for this api can be found in the api documentation.