Why does Gaff seem to not speak English at the beginning of Blade Runner, but is fluent at the end?

Question

It seems like Gaff speaks almost no English at the beginning of the movie, but has become conversant by the end. Is this deliberate? Why?

In one of the first scenes, Captain Bryant has sent Gaff (Edward James Olmos) to bring Deckard (Harrison Ford) to him. Gaff finds Deckard eating noodles, and begins speaking to him in a language other than English. Deckard does not understand him, and summons the elderly chef to translate, who shares that Gaff is attempting to place Deckard under arrest. Gaff eventually gets out the word "Bryant," which convinces Deckard to go with him.

Fast-forward about 2 hours to the scene where Deckard and Roy Batty are on the roof of JF Sebastian's dilapidated hotel. Gaff lands his police cruiser on the roof, and shouts to Deckard:

You've done a man's job, sir. I guess you're through, huh? It's too bad she won't live. But then again, who does?

I don't know how much time is supposed to elapse between those two moments, but it seems like it can't be more than a few days, perhaps a week. At the beginning of that week, this police officer cannot even say "you're under arrest" in English. At the end of that week, the same officer seems plenty fluent.

How can that be? Humans generally cannot gain language proficiency with anything like that speed.

Perhaps you're thinking: Gaff hasn't really learned English, he's only memorized a couple of statements. (Nevermind how he knew in advance what statements would be appropriate when he finally caught up with Deckard.) If that's the case, then why wouldn't he also know how to say bread-and-butter police stuff like "you're under arrest," or "get in the car?"

Is the implication that Gaff is a Replicant? Or is this a pair of identical twins who both work for Bryant, only one being fluent in English?

Answer 1

Gaff can speak English, but he chooses not to.

Indeed, as the OP mentioned, it is quite impossible that Gaff would learn English in a matter of a few days. Moreover, in the original book, Gaff has a slightly bigger role, and he converses quite a bit with Deckard about his job.

So why doesn't he use English?

Well, most likely because he initially dislikes Deckard and to show that he is better than him: The 'Cityspeak' is used by the criminal underworld, so by using it Gaff shows that he is a "professional cop", who is knowledgeable about the dangerous parts of the city. But instead of being assigned to chase the missing replicants, his boss — Bryant — sends him as an errand boy to pick up some washed-up ex-Blade Runner.

Also, as @PoloHoleSet mentioned in comments, Deckard most likely understands perfectly Gaff, but decided to be a pain in the butt and play dumb.