I see.
You mean, in https://discourse.example.com/admin/site_settings/category/required the field contact email.
This means that my site’s translation is broken and [it.about.contact_info] is a placeholder for the (unavailable)translated text.
This means I have to dive into D. translation for my language, which is something I tried to procrastinate as long as possible.
Thank you @thump, this issue may be closed for me.