I found the answer to my own question, sorry for the noise.
It said in /var/log/cups/error_log "Unsupported character set iso-8859-1"
So I searched about this; it seems that CUPS is most happy with UTF-8. Apparently Lotus Notes is using ISO8859-1 coding.
I created a notes-wrapper script, which sets UTF-8 before launching Lotus Notes:
Code:
#!/bin/sh
export LANG=en_US.UTF-8
exec /opt/ibm/lotus/notes/notes
I made it executable and call it in the application starter (.desktop file).
Now I can see the installed CUPS printers in the Lotus Notes print dialog.
Johannes