How to change the server header encoding when redirecting and return a 404 page without a redirect to https?

Question

Apache HTTP Server

There is a virtual hosting on TimeWeb.
The htaccess file has a redirect from www to non-www, from http to https:

AddDefaultCharset UTF-8
  AddType 'text/html; charset=utf-8' .html .htm .shtml

  # Перенаправление с www   
  RewriteCond %{HTTP_HOST} ^www.specpst\.com$ [NC]
  RewriteRule ^(.*)$ https://specpst.com/$1 [R=301,L]
  
  # Перенаправление с http на https 
  RewriteCond %{HTTPS} off
  RewriteCond %{HTTP:X-Forwarded-Proto} !https
  RewriteRule ^(.*)$ https://%{HTTP_HOST}%{REQUEST_URI} [R=301,L]
  ...
  # Перенаправляем в файл обработки URL
  RewriteRule ^(.*)$ /template/urlrewrite.php [L,QSA]

Redirects work correctly, but in the server response headers they give:
Server: nginx /1.10.1
Content-Type: text/html; charset=iso-8859-1
...
Depending on certain conditions, the urlrewrite file will incude a 404 error page.
Question:
- How to change the encoding of the server response when redirecting from charset=iso-8859-1 to UTF-8 (I assume that in the nginx settings because htaccess seems to be responsible for Apache, which are not available to me)?;
- How to immediately give a 404 error page without a preliminary redirect from http to https for example?