I'm trying to figure out if you can still create custom villagers that sell custom potions such as speed 10.
/summon villager ~ ~1 ~ {Offers:{Recipes:[{buy:{id:acacia_planks,Count:1},sell:{id:potion,Count:1,tag:{Potion:"minecraft:water",CustomPotionEffect:[{Id:3,Amplifier:2,Duration:180}]}}}]}}
The villager spawns however, the trade is just a water bottle with no potion effect.
VillagerData
tag has nothing to do with the fact potions are not working. Next time, please be sure to provide a minimal reproducible example. I've edited your command so that it is the bare basics of what is needed to solve the problem. – ExpertCoder14 Aug 26 '20 at 16:45