Minecraft Java Edition – Unable to Give Player Custom Splash Potions

Now I'm not a genius when it comes to command blocks so I can't tell you what is wrong but I remade your command and tested it in 1.9.2 (which worked) and by comparing my command and your command there is some differences.

/summon Villager ~ ~1 ~ {CustomName:"The First Wizard",CustomNameVisible:1,Profession:1,Career:1,CareerLevel:42,Offers:{Recipes:[{rewardExp:0b,maxUses:2147483647,uses:0,buy:{id:emerald,Count:1},sell:{id:potion,Count:1,tag:{display:{Name:"Super Potion"},CustomPotionEffects:[{Id:5,Amplifier:5,Duration:600}]}}}]},Attributes:[{Name:generic.movementSpeed,Base:0}],Invulnerable:1,PersistenceRequired:1,Silent:1}

The generator I made this with is

http://mcstacker.bimbimma.com/

It might be a bit confusing at first but it helps me make several of my commands. It even gives a description for all/most of the options it gives.

Hopes this helps!

As of 1.9, potions no longer use the Damage value to determine type of potion and whether or not it's a splash potion. Instead, the ID has been split into minecraft:potion and minecraft:splash_potion (along with minecraft:lingering_potion introduced in 1.9), while the effect itself is stored in the Potion string tag:

/give @p minecraft:splash_potion 1 0 {Potion:"minecraft:strong_healing",display:{Name:"Grenade"}}

You can find a list of default brew IDs here.