'Next Wednesday' is always the Wednesday of the calendar week following the current calendar week; doesn't matter what day of the week it currently is. 'This Wednesday' is always the Wednesday of current week on the calendar— even if that day is in the past.
Is it quirky that this expression doesn't instead mean 'the next Wednesday that will occur'? Yes, definitely. But I don't see how it's difficult to describe what it actually does mean.
That's the way it's supposed to be, at least as spoken in the part of Scotland from where my family hails.
But the Americans I know seem to get it wrong about half the time.
What I haven't figured out is if it's a regional (dialectical) thing, or just certain people being "dense", or simply never having been taught the rule.