Prevent server to change charset of html files

The server isn’t changing anything. And that’s precisely why you are having this issue. Modern browsers basically assume that everything is UTF-8. HTML5 only supports UTF-8 and nothing else. Your page uses a HTML 4 doctype, so it should still support other encodings. But then you will still need to tell browsers what the right encoding is with a charset meta tag. Right now, you have a page that’s not UTF-8, but do not include any information that tells a browser what encoding it should use. But I strongly recommend to just switch to UTF-8 instead. UTF-8 works everywhere, on all devices, for basically all languages, 100% future proof, with no other configuration needed.