How to bulk delete translation strings
If you intend to remove ALL strings imported through interface translation, you could execute something like this:

// Replace the empty string with your target language code.
$langcode = '';
\Drupal::database()
  -&gt;delete('locales_target');
  -&gt;condition('language', $langcode)
  -&gt;condition('customized', 0)
  -&gt;execute();


You may also want to reset the source file history information, so - if you change your mind afterwards - you can re-import the very same translations:

\Drupal::database()
  -&gt;delete('locale_file')
  -&gt;condition('language', $langcode)
  -&gt;execute();


or

locale_translation_file_history_delete([], [$langcode]);


As the locale module is making heavy use of static caches, you may run above commands in a dedicated process as, e.g. Drush PHP CLI (drush php:cli).