1 - Warlock magic is Legion magic, and the knowledge of it would be in Legion tomes and scrolls, which would be written in the Demonic Language.
2 - Our Minions speak Demonic. Supposing we didn’t know the language and learned our spells from “Translated tomes”. Well, we got plenty of teachers to spare!
3 - We literally have a spell that forces people to speak Demonic. How can we force people to speak a language we don’t know?
When and why was the option to do it removed?
The curse of tongues is really mean, please stop using it. Thank you, all Warlocks! <3
Our Demonic Language was tied to Metamorphosis and Dark Apotheosis. When those spells were taken from us to open up room for the new Demon Hunter overlords, the language was taken too.
Demonic is just Draenei language with more curse words.
Literally 
I want a Demon stable first before they add anything.
I’ll support this as long as Shadow Priests can speak Shath’yar all the time too.
Whenever I see an NPC or DH speaking demonic, not being able to understand it as a warlock triggers me.
Get Rosetta Stone and learn demonic while taking a dump, like a normal person.
Man you Locks really have sacrificed everything…are you sure you’re not a DH?
Of course I’m not a Demon Hunter!
I’m the exact opposite of a Demon Hunter!
I’m like a… Demon Vegan?
the ability to speak demonic is for demon hunters only. hope this clears that up 
Bob oepg ipsspfpi smbbi al dmddo!