In order to expand your vocabulary you must perform enough combos to receive around 60 different Combo Fanfare messages. Every time you perform a combo between the hits of 2 to 999 on your opponent, it will display a word under your combo number. There are around 300 total fanfare entries in all! There is a visual example of the combo counter below. Each number of hits has a word connected to it. An example would be the word, "Poetic" popping up whenever you do a 2-hit combo or "Adorable" when doing a 4-hit combo. You must receive at least 60 or so different words in order to unlock this. This can be unlocked across any mode (possibly even Training), but it may be easier to boost in 2 Player Versus.
2 Player Versus Method
Start up 2P Local Versus Mode and try using the following character's Blockbuster Moves (Supers) against your second controller. They will easily land you different combo messages in various ranges. You may want to combo in and out of each one to help add to your combo counter. Try starting out with 2 crouching punches then cancel into a Blockbuster or finishing with a Launcher (followed by some attacks) to add more hits. Double's Cattelite Lives and Megalith Array are both "mash-able" Blockbusters, so you can quickly press buttons to get various different quotes there as well. Experiment!
Peacock's Argus Agony: + + (20 Hit range)
Double's Cattelite Lives: + +(60 Hit range)
Double's Megalith Array: + + (Varies)
Parasouls' Inferno Brigade: + + (20 Hit range)
For a full list of all Combo Fanfare messages click HERE. You can check them off as you pull each combo word off. Once you have 60 or so different ones appear, the achievement will unlock.