Translatable rich text configuration
I was playing with configs and finally found a solution. The configs should be:

langcode: en
more_info_text: 'More info'
first_link_list:
  format: 'full_html'
  value: ''
second_link_list:
  format: 'full_html'
  value: ''
third_link_list:
  format: 'full_html'
  value: ''


And the scheme file should not contain the following line

class: '\Drupal\Core\TypedData\Plugin\DataType\StringData'


Another thing I noticed is that you should translate the whole custom form, otherwise it will give an error at config inspector, so in my case I had to split my form into general and language specific. 

Hope this helps somebody