It's pretty much your standard battle banter, ala Persona 3/4.
Most of the pre-action comments are along the lines of being unsure if an attack will or won't work (when you either have or haven't figured out the weaknesses of an enemy yet), a teammate saying they'll either be able to jump in for a successful session attack or that it'll fail, or some phrase of thanks/relief for a heal or buff.
The lines during actions are the typical success/failure fare of "I did it," "This is going to hurt," "No way," though along the generic stuff there's a couple lines more in context to the type of attack (i.e. comments about freezing cold for an ice attack). The stuff during sessions is also fairly generic, sometimes with callouts to the next character coming in the pain parade.
Of course, the special attacks, adlibs, duos, etc are pretty specific lines.
There's fun conversation bits between the Mirages and the characters once their turn begins too.
I might be incorrectly remembering a few, but I think this is how a couple go...
Caeda/Tsubasa
C: "You're cute, Tsubasa."
T: "Eh... EH.....?"
Chrom/Itsuki
C:I "We'll overcome fate!"
or
C: "I don't know if I can do this..."
I: "I'll protect you with everything I have!"
Cain/Touma
C: "Don't overexert yourself."
T: "Don't worry."
T: "Cain, lend me your strength!"
C: "But of course!"
Draug/Mamori
M: "Pace yourself properly! 1, and 2, and..."
D: "Understood!" (switches up his counting type for some reason)
Tharja/Kiria
T: "Ehehehheheheh...EHEHEHEHEHE"
K: "W...what the hell, Tharja..."
There's also a bunch of lines for when characters get hit with certain status effects, or if a preceding character got KO'd, or if you're wearing a certain costume.