Q:

How does Bumblebee speak English as soon as he arrives on Earth in the Bumblebee movie?

In the 2018 Bumblebee movie, Bumblebee speaks English to John Cena's character as soon as he arrives on Earth in 1987. But how does he know English?
In the original live action Transformers from 2007, Optimus Prime explains that the Autobots learned English from the "World-Wide Web." But in 1987 there was no World-Wide Web to monitor. So how can Bumblebee speak perfect English?

A:

Bumblebee demonstrates a capacity to use radio signals in order to (re-learn) English when his vocal unit is damaged by Decepticon fire and subsequently replaced. Note that this would also strongly suggest that he's not speaking English, but rather his vocal unit is translating spoken Cybertronian into English. 

Charlie and Memo stared at the radio, then looked at each other. Charlie returned her gaze to the radio and said, “Whoa, wait. Is that why you’re always messing with the dial, Bee? Are you teaching yourself to talk?”
  Bumblebee readjusted the dial to play the lyrics from a song by the Four Seasons. “Walk like a man, talk like a man.”
“No freaking way,” Memo said.
“Bee, you’re a genius,” Charlie said. “An actual genius!”
Bumblebee: The Junior Novel

Given that someone traveling at greater than the speed of light would have access to 50+ years of radio traffic, it's certainly possible that he taught his voice unit English in much the same way when he first arrived.

