Hi, when I return a string like ÄÜÖ the browser is interpreted as

ÄÜÖ

fastify will respond with

content-type: text/html;
content-type: application/json;

it's obvious that I use the wrong charset but UTF8 is defacto standard and should be used as default.

content-type: text/html; charset=utf-8
content-type: application/json; charset=utf-8

A Unicode encoding such as UTF-8 is a good choice for a number of reasons.

References:

• https://www.w3.org/International/questions/qa-choosing-encodings
• https://www.w3.org/International/articles/http-charset/index#charset