Configure Always On to use secondary site as DR I have two SQL Server 2017 Standard Edition clusters, each in a different datacenter, only a pair of servers each.

I was able to configure and test the Windows Cluster, Quorum for it, AG, including failing over from primary to secondary, and created one listener for each.

How do you think I can replicate to second DC?

I can't upgrade to SQL Server Enterprise to use Distributed AG.
Standard Edition availability groups are limited to one replica, which is clearly stated in  the documentation at Basic Always On availability groups for a single database.  So if you need to maintain a another copy, you'll need to use a different option.

Some possibilities are:  


Log shipping
Replicate the entire server at the virtual server's host layer with something like Zerto
Replicate the storage at the storage layer
Replicate the database files with a third party product that performs host-level file replication (e.g., Carbonite Double-Take).