Translation

As you haven't a Delete button on interface translation page, you can't do that from the translation interface. But you can do in a small custom module.

Example : Delete string ID 346, 'Home'

To get languages in English:
$site_languages = \Drupal::languageManager()->getLanguages();

To get languages in native language:
$site_languages = \Drupal::languageManager()->getNativeLanguages();

Programmatically create and translate nodes.

Exemples:

$translation = $entity->getTranslation('de');

Drupal 8

//To get the lanuage code:
$language = \Drupal::languageManager()->getCurrentLanguage()->getId();

//To get the language name:
$language =  \Drupal::languageManager()->getCurrentLanguage()->getName();