I'm sorry I'm still new to some of the Mugen stuff but basically how I added quotes to Akira's Seph and how Infinite adds quotes to his characters is under statedef 180.
To be specific you type in

[State 180, Quote]
type = victoryquote
trigger1 = 1
value = 1 + (random % 10)

for normal quotes and for character specific quotes

[State 180, Victory Quote vs. Character name]
type = VictoryQuote
trigger1 = var(40) != 1
trigger1 = Enemy, Name = "Character name"
value = 30

For the character name, don't use the display name, use the name inside the .def file.
Ex: Name: Cloud Strife
Display Name: Cloud
Hopefully this helps a little. I'm not the best at mugen stuff myself.