Thank you for this very detailed and yet to the point report!

Unfortunately, I cannot reproduce the issue you see with:

c:\Users\Corion\Projekte>perl -v

This is perl 5, version 20, subversion 1 (v5.20.1) built for MSWin32-x
+64-multi-thread

Copyright 1987-2014, Larry Wall
[download]

Also, I had to remove the following line, as it seems that my version of locale doesn't know about :ctype:

use locale ':ctype';
[download]

The Linux 5.18 I have, doesn't want to know about experimental, so I can't meaningfully test it there either. If I remove the mention of "smartmatch", no warning happens, but that just matches your description.

Update: After installing experimental, I have no change in my installation of 5.18. But it also doesN#t want to know about use locale ':ctype', so I might still be missing something there.