For "c3 a4 c3 b6 c3 bc c3 84 c3 96 c3 9c"

There are 12 bytes in total, for a UTF-8 encoding, "c3" represents that it starts a two bytes character, so there should be 6 characters in total,

c3 a4
c3 b6
c3 bc
c3 84
c3 96
c3 9c

While length of unreadable character "üÃÃöäÃ" is 9, I don't understand why.

But I have encoutnered a similar issue once, and solution was as beblow, maybe you could try this,

1) set tHttpRequest.ReadRawMode = 1 
2) read the response to a string, let's say "str", convert it, $ZCVT(str, "I","UTF8")