The best thing to try is forcing the server to use UTF8 and setting the client to use UTF8.
SecureFTPConnection will try to force the server to use UTF8 (1) the CommandEncoding property is set to UTF8 before connecting and (2) the AutoFeatures property is set to true. If these conditions are met then you should see the client sending the command "FEAT" and, if the OPTS feature is supported, "OPTS UTF8 ON". If the server responds with a 200 then it should work.