Apache Module mod_mime

The HTTP Content-Encoding representation header lists the encodings and the order in which they have been applied to a resource. This lets the recipient know how to decode the data in order to obtain the original content format described in the Content-Ty

As the warning suggests for ideal performance your server should be adjusted to serve these files with the HTTP Content-Encoding header. (see here for more details on Content-Encoding).

Languages and content encodings are treated accumulative, because one can assign more than one language or encoding to a particular resource. For example, the file welcome.html.en.de will be delivered with Content-Language: en, de and Content-Type: text/h

Accept-Encoding 和 Content-Encoding 是性能优化关键：客户端声明解压能力，服务器按需压缩，实测文本资源体积可减 60%-80%。 本文手把手教你搞定旧浏览器兼容、CPU 负载等难题，让网站在各类网络环境轻快运行，告别 “传输慢” 痛点。

So if you have a file whose names ends in .html.utf8, apache will serve the page as if it is encoded in UTF-8 and will dump the proper character-encoding directive in the header accordingly.