Locke talks a lot, and he has a few of the game's better lines. In the Japanese, he uses very informal speech structures, which I've heard make him seem like a "badass." I'm not sure how you'd translate that, but in my head Locke's always had a bit of a cockney accent. Not enough to be annoying, mind you, just enough to be interesting. However, that's in my head, which is far too occupied with Locke in the first place.
TERRA: Empire...but I'm a soldier of the Empire...!
LOCKE: That's not true! They were using you! Things are different now.
TERRA: I don't understand... What should I do?
LOCKE: I can't tell you what to do.
You don't have to decide right now. You'll soon find your way...
TERRA: But how will I know which way is right...
Tina: Empire... I'm a soldier of the Empire...
Lock: ... you WERE. An enslaved lie of a person. But it's different now.
Tina: I... don't get it. What should I do... my head... hurts.
Lock: It's that you have your own free will from now on.
You probably shouldn't think too deeply about it. I'm sure your path will become clear to you.
Tina: Free will...
This is a conversation between Locke and Terra, before they go to bed in Figaro castle. The first version is the American script, the second version is an unofficial translation of the Japanese. The major difference is that Locke's a lot more self-assured in the second version, which is true throughout the entire game. This is partly due to the overuse of exclamation points throughout what we know as Final Fantasy III, and I guess Locke just seems a bit more competant without them. And he also says that deep thinking causes headaches. Which in my case, it does. Ow.
Locke: Let's go!
Celes: !? You'd take me along?
Impossible. I can't run... (takes a few steps)
Thank you... but, I owe you. Even if you took me out of here you wouldn't be able to protect me without risking yourself...
And if that's the case it would be better for me to unhesitatingly face my death here.
Locke: I'll protect you!
(Celes blinks) Locke: I will protect you, you'll see!
Celes: Why did you say you would protect me...?
Locke: You resemble...
Nah, it's nothing. I just feel like it.
This is, again, a translation of the Japanese script, not the official American version, because it makes a whole lot more sense. It shows Locke's real need to run around rescuing people, even if they're complete strangers and have a history of torching Maranda. It's also the first interaction between Locke and Celes.
"Hey! Call me a treasure hunter or I'll rip your lungs out!"
"Here now, say treasure hunter, willya?"
The first is Locke's most famous line in the official translation, the second is a direct translation. They're both funny in their own way, and both times this is followed by Locke stealing the clothes off someone, which is undeniably cool.
"I... couldn't protect..."
In the Japanese version, this is Locke's mantra. He repeats this over and over again, of course in reference to Rachel. This is the force that drives his character, beyond the love of adventure or hatred of the Empire.
"Not a word of this, O shrouded one!"
When Locke gets sea-sick on the boat to Thamasa, he's a bit embarrassed but still smart-alecky. I mean, he's talking funny to Shadow, for goodness sakes!
"I'll never let go. I promise."
Locke holds on to Celes, who has fallen off a ledge, in a reenactment of the Rachel tragedy. This, time, though, he doesn't let go.