Oh, one other thing: if the theory about gettext delivering the "wrong"
encoding is correct, then the error messages going into the postmaster
log should be in WIN1252 encoding, rather than UTF8 which is the
intended behavior when server_encoding is UTF8. The log snippet in your
bug report was UTF8, but that might have gotten converted somewhere
along the line. Can you confirm which encoding is actually present in
the log file?
regards, tom lane