Hello,
I configured several PostgreSQL (1C edition) clusters on the same server on different ports: 5432, 5433, 5434.

However, with 1C enterprise tool I can add a new 1C database only to the first cluster with a default port (database server = "localhost").

If I try to add a DB with database server "localhost:5433", I get an error message "could not translate host name "localhost:5433" to address: Name or service not known".

Is it at all possible?

As I know its impossible.

But you can try use IP aliasing. I hear that someone use it successfully.

Thank you for the idea, Ivan.

It was very easy to reconfigure my three PostgreSQL clusters on Ubuntu:
I just added two aliases (http://www.cyberciti.biz/faq/linux-creating-or-adding-new-network-alias-to-a-network-card-nic/)

And changed three settings in each postgresql.conf file:
listen_addresses = 'IP address of the interface to use for this cluster'
port = 5432
unix_socket_directories = 'Different path to use for this cluster'

And then adding a 1C DB to the required cluster is easy. Just point the "database server" to the IP configured in listen_addresses.

I think that adding two aliases broke my 1C test server's licensing. The server (8.3.5.1119 64-bit) is running on the same Ubuntu host as PostgreSQL clusters.

At first, after adding new aliases, it worked, but after ~30 minutes I couldn't open any configuration and was shown various cryptic messages about missing server license file, missing server license, no licenses available, etc.

I stopped the server, deleted everything from /home/usr1cv8, restarted the server, re-added all test databases.
Now everything works as expected.

This might be caused by other reason. You had not to acquire a license, so the license was fine, but maybe some other reason did not let the 1C:Enterprise to validate the license.