I don't see an issue here. If you are installing the Polish language, why would you want "Desktop" instead of the Polish equivalent? Are there applications that don't use the localization? If so, bugs should be entered for those applications. Isn't there a freedesktop.org environment variable applications should be using instead of $HOME/Desktop? (Maybe $HOME/$DESKTOP or $DESKTOP_LOCATION ?)
this always seemed a solution looking for a problem to me: a lot of hassle and issues, not 100 integrating applications and such... all to have "scrivania" (for me) instead of desktop and a couple of other folders such as Video and Music... they are all terms any pc user (including the ubernoobs) have no problem with. I'd welcome an option during install to just disable folder localization instead.
For example, in Portuguese the folder "Desktop" becomes "Área de trabalho".
I don't like it that way because:
1. It has spaces, which makes using it inside the shell hard and through SSH, impossible.
2. I like standardized names (Desktop for the desktop, Documents for the document, Music for the music folder, ...)
3. I like English better xD