"I wish you'd say that" is short for "I wish you would say that." Relating to time, it could be general, "I wish you would say that (sometime/all the time/more often/in the future)" or at this exact moment "I wish you would say that right now." "I wish you said that" can mean the same thing as that first meaning "I wish that you said that (sometime/all the time/more often/in the future)" but native speakers usually mean to say "I wish you'd said that" but drop the 'd, sometimes even in writing. When I first read your question, that was what I thought you had typed at first glance. "I wish you'd said that" is short for "I wish you had said that" meaning "I wish that you had said that" (in the past, likely because it is too late now) I hope that answers your question

The first is "I wish you would say that" - conditional This is a wish that the person would say something - so you know what the person wants or thinks. The second is "I wish you (had) said that" - past tense This is a wish that the person had said that in the past - so you would have known what the person had wanted or thought.

That exact phrase may be uncommon, but the idea of it "I wish you'd..." is common. "I wish you'd be honest with me." "I wish you'd text me instead of calling." "I wish you'd show up on time."

So, other things aside and the excellent answers below aside, the first one is really unlikely: an unusual thing to say. .