Scripter API
Scribus can be automated using the powerful Python language via the scripting API. The reference manual can be viewed by selecting Help->Scripter Manual from the Scribus menu. On Windows select Help -> Scribus Help ... and navigate to For Developers -> Scripter (version 1.6.4)
It is also possible to open the script console from the script menu and execute the following script
import scribus
help(scribus)
This gives you a comprehensive list of the available methods and parameters implemented in your current version.
The web site https://impagina.org/scribus-scripter-api/ describes the API of version 1.7.
Scripting functionality will only be available if your version of Scribus was built to include it. Some binary packages (rpms, debs etc) don't include it and scripting functionality will therefore be unavailable.
It is also possible to automate Scribus in C++ using the Plugin Architecture.