Burp Proxy is the go-to tool for web security testing (ZAP is still completely unusable for anything else than "auto-scan, eat all my ram and crash", but I would be happy to be proved wrong.), so it's always interesting to find some bugs in it: some are stockpiled for CTF, the others are going into websec.fr, like this one, that is still unfixed.
Burp is giving priority to the html tag
over the one sent by the web server, while everyone does it the other way. This
means that when you're serving UTF-8 content with the
http-equiv="content-type" content="text/html;charset=UTF-16"> tag in the
webpage, Burp will try to decode its content as UTF-16, yielding a lot of weird
(usually Chinese, but I don't have the required fonts to display them correctly) characters:
This can be fixed by forcing Burp to use UTF-8 in User options -> Display -> Character Sets -> Use a specific character set.
This is the correct expected result: