Please allow for redirects from pl.wikimedia.org to happen via interwiki links.
The interwiki prefix wmplsite: has recently been added.
If I'm reading the docs right, to make this work we also need $wgDisableHardRedirects to be set to false.
Example redirect page:
pl.wikimedia.org was used as the outward-facing site for Wikimedia Poland. This function has now been moved to wikimedia.pl. The wiki will continue to serve as a resource for members and a storage mechanism for public information about the chapter. Due to this split of functions to two distinct sites, we need to seamlessly redirect certain pages from pl.wikimedia.org to wikimedia.pl
Thanks in advance.