I think perhaps you misunderstand: because each theory has zero evidence, each has zero truth to it (however you want to word "truth", maybe pick from the above list).
Because they both have zero truth, they are equally untrue, meaning an equal amount of untrue: zero in both cases.
Turns out there's no contradiction, and no truth to either!
> OK, that's what I had thought you meant! But that position isn't found anywhere in the Wikipedia article.
It actually is! I even quoted it a couple times up in this thread :) Maybe you're confused over effectively true vs practically true vs true vs. etc, but that's just semantics, they all mean the same thing!
> Also, what if two contradictory propositions each have zero evidence, are they then both untrue?
It depends, can you give details (what are the specific propositions)? For example, Russell's teapot explains when the "contradiction" is between the teapot existing without evidence vs. not existing
Practically untrue and untrue don't mean the same thing.
You could argue that they could be treated as if they mean the same thing (in some limited scope), but that is different to them meaning the same thing, and, since such an argument is not presented in the Wikipedia page (rather, a contrary position is presented by Russell in the second quotation on that page[0]) you would have to make that argument yourself.
[0] He makes an explicit distinction between what he ought to call himself if being purely logical and what he practically is (an agnostic and an atheist, respectively).
You could hold these two positions simultaneously without there being any contradiction:
* they are both equally untrue.
* they are both true