How to check if an edited form is editing a translated node
I could answer myself for the first question. The following line will give me the edited language.

$form_state-&gt;getFormObject()-&gt;getEntity()-&gt;get('langcode')-&gt;value;


But, maybe, the following is better:

$is_original_language = $form_state-&gt;getFormObject()-&gt;getEntity()-&gt;get('default_langcode')-&gt;value;


It is better, because original language could vary. In this case on the Add/Edit Node, Add new translation and Edit translations the return value can be parsed directly. Add Node or add new translation returns a Boolean while the edit forms return an int (1/0).