Let's assume that the WoG is that you cannot lie using parseltongue. We can play clever tricks with what it means to lie, but trying to apply a definition that was only formed after parseltongue was created does not mean parseltongue cares one bit how someone else chose to define truth.
The only definition that parseltongue cares about is the one that it follows. The others might be useful in their own domains, but aren't guaranteed to apply to parseltongue.
Flying broomsticks didn't suddenly stop working the way they were designed just because someone discovered how physics actually worked in the real world. Invisibility cloaks haven't stopped working simply because they've been demonstrated to be impossible based on elementary logic rules. Magic doesn't care and parselmouth doesn't care either.
At best you could use some knowledge about how language works to devise experiments to test how parseltongue actually works (you would be relying on WoG responses though) but to claim that it's impossible because of some language rules we've cooked up say it should be impossible is trying to fit the outcome to the theory which is not how science works.
But if we're going to insist that parseltongue can't work and is a therefore bad, why are we okay with anything else (invisibility cloak, time turners, etc.) that we can't adequately explain because they also fly directly in the face of what all of the rules we have developed say is not possible?
Rules of the universe in which the story takes place allow for a language where the speaker is apparently incapable of knowingly telling a direct lie. We don't know all of the rules and can't test them (outside of WoG) because the universe does not actually exist in any form that allows us to get definitive answers to experiments. At best EY could provide outcomes for us, but I suspect that the outcomes would all indicate that it doesn't matter what fancy rules of language or logic you are attempting to use, they don't work because snakes can't lie. Why? Because a wizard did it.