The problem was:
Viart Shop sets the character encoding by the set in message.php. In hungarian that was iso-8859-2 (latin2).
When I look at the shop, this was showed in utf-8. I was able to set this to the correct iso-8859 manually in browser, but if I browse the shop, the utf-8 appears again.
UTF-8 did not shows the ú,ó,ü,ö, etc. chars, is in hungarian language.
The solution:
There is a messages-utf8.zip file in the shop's messages folder. I used them, replaced the normal ones, and this works...