I have noticed that the French and Farsi Wikipedia have new side menus (the left column navigation menus) that can be shown/hidden.
Topic on Skin talk:Vector
Yes, it's a part of the desktop improvements projects. The wikis you mentioned (plus some more) have the improvements deployed early. Logged-in users can opt-in/out on all wikis from the "Appearance" tab in Special:Preferences.
Does it possible to return to the last appereance? The waste of space make me sick. I hate needing to scroll and not seeing all the informations im looking for
Edit- ...I finded the checkbox for legacy apperance