Hi Niels--
i notice that https://www.lysator.liu.se/~nisse/nettle/nettle.html is served with the HTTP header:
Content-Type: text/html; charset=iso-8859-1
but it contains non-ASCII text -- your name "Niels Möller", but it is rendered as Niels Möller due to the charset parameter.
You can update your nginx config by using the charset directive:
charset UTF-8;
see https://nginx.org/en/docs/http/ngx_http_charset_module.html#charset for more detail.
Regards,
--dkg