plwikisource community decided here:
https://pl.wikisource.org/wiki/Wiki%C5%BAr%C3%B3d%C5%82a:Skryptorium/Pulpit_techniczny#Lokalne_.C5.82adowanie_plik.C3.B3w
that we want the sidebar link pointing to commons file upload (commons:Special:UploadWizard).
User:Nemo_bis suggested here:
https://meta.wikimedia.org/w/index.php?title=User_talk%3ANemo_bis&diff=9070435&oldid=9069800
that it can be done by setting the $wgUploadNavigationUrl variable to:
'//commons.wikimedia.org/wiki/Special:UploadWizard'
Please set this variable for plwikisource.
We want local file upload be still available to all users via Special page(s) as it is now, so no other change is requested in this matter.
Version: wmf-deployment
Severity: enhancement