First of all, ščavo is a very offensive name that Italians in Trst, Gorica and elsewhere on the border like to use to piss of either members of the Slovene minority or Slovene visitors. Very provocative, very insulting.

There is nothing unusual about Sava not being Slavic. Our ancestors adopted and slovenised many place names at their arrival here. Names like Celje (from Celeia), Ptuj (from Poetovio) and as you noticed also Sava from Savus.

Where the hell did you get Šavli?! ;D IMO noone will take you serious on a site like this if you come up with various Šavlis (especially if they're doctors and their names are Jože) …