In Patch 11.1, you can buy 
Elixir of Tongues from a vendor in Undermine. The elixir allows you to understand the opposite faction for 1 hour for just 30 gold.
Where to Get the Elixir of Tongues?
To get your hands on this elixir, head to Undermine and find Fizzi Liverzapper. To locate the NPC:
- Go to The Low Blow in Undermine at /way #2346 28.95, 27.05.
- Open the sewer grate and enter the hidden area.
- Find Fizzi Liverzapper at 28.97, 25.25 and stack up on the elixir!
Apparently, the same vendor (Fizzi Liverzapper) is selling the elixir in Dalaran’s Sewers, according to Wowhead.
Gold Making Opportunity?
The elixir can be traded, meaning you can sell it in the Auction House. Not everybody knows the item can be purchased from vendors… well, until now.
