only HTTP "Vary" header where it is needed

HTML content on f-droid.org has the "Vary" header set to:

"Vary: negotiate,accept-language"

You can check headers with "curl -IsS "https://f-droid.org/"

This header is notoriously bad for caching performance as it results in many, often identical versions of the same content in the proxy's cache. You can read about this at https://www.fastly.com/blog/best-practices-using-vary-header

AFAIK, f-droid has the language specified in the URL and it never serves different content based on the "accept-language" request header. If I am correct, then please remove it from the vary header.

The "negotiate" header is a bit of a mystery to me. My browser does not send it. Ideally, one would remove the vary header entirely if that does not break things.