Show English when there is no translation
Language fallback module

I haven't tried this module but it seems to do what you're asking for. You can edit bg, de, it etc languages and set English as the fallback. 

Drupal 8 also has one extra module for this: Entity Language Fallback

Automate with Rules

You could probably come up with a Rule that automatically saves translation nodes of an English node under certain circumstances, with some custom code. 

Quickly fill in translations

If you can't do custom code for what ever reason, you could enable Synchronize translations (which is a submodule of i18n) on your Content types. This way when you go to translate other languages you'd already have the English text filled in, images kept etc so you just Save the node and see English text on an Italian node.