They don't stack because they do the same thing. Neither ability is "increase your critical range by one". They both make your critical range 19-20. It doesn't how many times you make int 19-20, it's still going to be 19-20.
It's just like the fighting classes' extra attack abilities: They don't give you +1 attack -- they let you take two attacks when you take the attack action.
Champion- 19-20
Hexblade Curse- 19-20
Would that make the extended critical 18-20 if they were both active?
Wolf
no
To clarify further:
They don't stack because they do the same thing. Neither ability is "increase your critical range by one". They both make your critical range 19-20. It doesn't how many times you make int 19-20, it's still going to be 19-20.
It's just like the fighting classes' extra attack abilities: They don't give you +1 attack -- they let you take two attacks when you take the attack action.
Thank you for the information. Is there any other way to increase your threat range? IE: race, class, ability, feat, etc.
Wolf
The champion has superior critical at higher level.