Translation helpers enables other modules to respond to changes in the "source translation" of a set of translated content. This functionality is useful for modules that track data by the "source translation" (node.tnid value).
This module doesn't do anything on its own. You should install it only if it's suggested or required by another module you're using.
The module also provides other methods for modules to use with translated content.
Drupal 8
A Drupal 8 version won't be needed. Translation Helpers addresses use cases related to the model of translation used in the Drupal 7 core Content Translation module, in which each language has its own node. Drupal 8 has switched to fields-based translation, in which the awkward workarounds of D7 will be a thing of the past.
The shared email module allows multiple users to use the same email address for different accounts. The module works for both registration and account updates.