WPML. How to connect post translations from frontend form ( or throught php )?

My task is that user should be able to create posts from front-end. I'm using ACF plugin, for creating forms on front-end.

My web is in 2 languages: Rus and Est. User can create on one of that language and than should be able to create a translation to it.

So my question is how to:

1. Check if there's already translation for these post ( in both directions, if i create first on Rus and i need to check if there's Est translation and if there is - get the id of the post for future needs )


2. Make it a translation of certain post ( on save post_save ) [ ex. I have post on Rus, now i submited on Est lang. and how to connect them togethere ? ]

Thanks in advance )