You want to go to the Swift project page on GitHub.
The Swift Programming Language. Contribute to apple/swift development by creating an account on GitHub.
github.com
Then enter FreeBSD into the GitHub search bar and select
this repository, now find out, that a lot of work is done for FreeBSD. Finally find this one:
These changes make Swift build on FreeBSD (tested on 13.0-RELEASE-p1). There are some tests that I had to XFAIL, but the majority works. SourceKit tests are very unstable and seem to fail when too ...
github.com
So, there is a pull request for letting the current Swift project build on FreeBSD 13.
My advice is, to forget the Swift noobs on these forums, but instead try to build Swift on FreeBSD 13 after applying said pull request, and ask for help on the Swift project page.