Translate variable strings from site.yaml?

Hi!
I'm successfully have translated template strings with |t filter.
However, some string left untouched.
There are few left from site.yaml file:

title: Default lang title
default_lang: en
author:
  name: Default Lange Name
  email: Default email
  copyright: 'Default  copyright'

These strings are displayed with the help of {{ site.author.copyright }} from html.twig template.

My logic was to append lanuage.yaml with these variables. however this doesn't work:

non_en_lang:
  SITE:        
    TITLE: NON EN TITLE
    DESCRIPTION: NON EN DESC
    AUTHOR:
       COPYRIGHT: NON EN COPYRYGHT

Is it possible or there is another approach?
I've tried the {{ site.author.copyright|t }} but this doesn't work