19th.
I'm kinda with oakthorn here - is it regional?
I'm in NI, and I would say:
"Last Wednesday" = 5th.
"Wednesday" = 12th.
"Next Wednesday" = 19th.
"Wednesday after next" = 26th.
Then that would all change come Monday.
I'd only say "this Wednesday" if I was speaking on the Monday or Tuesday before the day itself 