tsi

This module provides a drush command and a service to add UI translations.

Drush

Add a single 'singular' string translation:
drush tsi "example" "Beispiel" "de"

Add a single 'plural' string translation:
drush tpi "1 example" "1 Beispiel" "@count examples" "@count Beispiele" "de"

TSI Service

You can also use the tsi.service to add translations. For example in a update or deploy hook:

\Drupal::service('tsi.service')->addTranslation('example', 'Beispiel', 'de');
\Drupal::service('tsi.service')->addPluralTranslation('1 example', '1 Beispiel', '@count examples', '@count Beispiele', 'de', '');

To import multiple strings you can use:

$translations = [
  'cat' => 'Katze',
  'dog' => 'Hund',
];

\Drupal::service('tsi.service')->addMultipleTranslation($translations, 'de');