http://bugs.winehq.org/show_bug.cgi?id=11442
--- Comment #7 from knan-wine@anduin.net 2008-02-02 12:14:39 --- If I understand you correctly, simply using these commandlines should be enough? "LANG=pl_PL.UTF-8 wine setup.exe" and "LANG=pl_PL.UTF-8 wine installedapp.exe" ... you're not changing system settings.
Anyway, this isn't the right forum for discussion. Ask on wine-users.