I know that Paragraph field itself are not translatable for some reasons. I wanted to know if we could still have separate number of paragraph items between two translations of a node.
Node 1 FR
Node 1 EN
I found no clear explanations on that.
Not really in an easy way. We're working on an alternative approach to making the field translatable in the experimental paragraphs collection project: https://www.drupal.org/node/2846682.
Basically, this adds a setting to optionally control visibility of a paragraph in another language. This is a useful approach for use cases where differences between language are the exception and not the rule.
You can also build something similar yourself with a standard list field or an entity reference field to languages and then implement something in preprocess, twig or entity access to hide the paragraphs based on that.
But the only way to have completely different paragraph structures is to have the field translatable, and that's still a work in progress.