I had faced the same issue during the installation of Sitecore 9.3. It was because the certificate already exists with the same Sitecore instance name in my machine.
I have followed the below steps to get rid of this:
Removed the certificates from my machine with the same instance name
Removed the Sitecore instance from the inetpub ...
As mentioned in the comment, instead of triggering a publish for each item, you may trigger it via an incremental publish.
You need to remove the ForLoop on the items. Below is an updated code snippet
var languageList = new List<Language>();
Database db = Factory.GetDatabase(this.sourceDatabase);
foreach (Language language in LanguageManager....
This issue happens when there is more than one DLL with the same controller name in the application. Then the conflict will arise because the DefaultControllerFactory would not know which controller to create. For example in your case, Twitter action exists in both assemblies:
In order to resolve this ...
What I understood is: you want to use an existing Solr Service (url), as you are installing Sitecore offline using SIA.
To achieve this do the following:
First make sure the solr service you created is running and the solr instance is accessible through the url. The default url would be https://localhost:8983/solr.
Now, from SIA, skip the "Install ...