Hi,
here is the reply from XMLRPC server:

HTTP header:
---------------
HTTP/1.1 200: OK
Content-Length: 921
Content-Type: text/xml; charset=utf-8
Server: WEBrick/1.3.1 (Ruby/1.9.1/2010-01-10)
Date: Thu, 18 Nov 2010 07:57:17 GMT
Connection: Keep-Alive
---------------

XML response (should be one line):
---------------
<?xml version="1.0"
?><methodResponse><params><param><value><struct><member><name>result</name><value><string>ok
</string></value></member><member><name>program_ver</name><value><string>10.0.1153</string></value></member><member><na
me>engine_ver</name><value><string>10.0.424</string></value></member><member><name>virus_db_ver</name><value><string>42
4/3263
2010-11-1</string></value></member><member><name>threat_desc</name><value><string>郈把快忱快抖快扶
志我把批扼 EICAR_Test </s
tring></value></member><member><name>infections_found</name><value><string>1</string></value></member><member><name>pup
s_found</name><value><string>0</string></value></member><member><name>infections_healed</name><value><string>0</string>
</value></member><member><name>pups_healed</name><value><string>0</string></value></member><member><name>warnings</name
><value><string>0</string></value></member></struct></value></param></params></methodResponse>
---------------
As you can see, there's correct UTF-8 string in cyrillic in the middle
of the XML.

BTW, botp's suggested solution (Encoding.default_internal =
Encoding.default_external = "UTF-8") doesn't work in Apache module
Passenger 3.0.0