How do I filter entity reference fields based on language?
The logic that defines if entities should be shown is in \Drupal\Core\Field\Plugin\Field\FieldFormatter\EntityReferenceFormatterBase::getEntitiesToView()

As you can see, translation is checked there, but the API doesn't directly support skipping something, the hooks behind that only allow to control applicable fallback languages and their order.

It's possible that you can use entity access, which is checked after that. Implement hook_paragraph_access(), for the view operation, check if the paragraph has a translation in the current content language and if not, forbid access. The same should work for your other entity reference, it's the same could, just implement hook_ENTITY_TYPE_access() for that too.

If that doesn't work, you can write your own field formatter plugin and override that method.