… are they human?
And if they are, how did they get so far from Earth?
And how can they speak such fluent English, with American accents even?
I believe the “A long time ago in a galaxy far far away” thing was really just an inside joke that this story would be like a fairy tale. It certainly seems more like a futuristic setting than a past setting. One where everyone speaks English of course—some British, some American.
They’re human, but not Earthlings. The canon answer is that humans are the most diverse species in the galaxy, and they essentially have the same biological structure as we do.
If they’re not, Uncle Owen made a huge mistake buying a protocol droid.
He had no need of a protocol droid
They’re human for the exact same reason that Aragorn son of Arathorn, Jon Snow and Geralt of Rivia are human.
The word they use to describe themselves sounds like “human” when translated to English. But they are from long long ago in a galaxy far far away, so they almost certainly predate the evolution of humans on Earth.
I thought JRR’s conceit was that the Lord of the Rings did actually happen on our Earth? That he was merely translating ancient documents he found?
They are certainly members of the most widespread sapient species in their galaxy (which has had interstellar travel for long enough that the original homeworld of that species may well have been forgotten). And their first language, like most members of that species, is the most-used language in that galaxy. But I think that, just as their language is “translated” to English to make it easier for us to relate to them, so too their species was “translated” for our benefit, and that their actual appearance is no more similar to ours than is any of the other sapient species they interact with.
What the hell you talkin’ bout? They’re speakin’ 'Merikin, just as Gawd intended! We’re dominant here, we’re dominant in the whole universe!
USA! USA! USA!
Yes that’s correct. John Rateliff argued that this feature of his mythology gives it an air of sorrow and poignance missing from most other fantasy, since the whole elaborate world that he so laboriously built up he also completely destroyed by setting in Earth’s prehistory. As Tolkien says of Arwen’s death, “and all the days of her life are utterly forgotten by men that come after.”
I have a theory about how the main characters in the Star Wars movies could look and speak like present-day humans, despite the series supposedly going on long ago in a galaxy far away. When a movie today is made that’s set in classical Rome, the characters do not speak in Latin. They speak in English (or whatever is the language of the country where the film is made). A movie must be a translation of the actual action, even if it supposedly is about a real event. In the same way, the Star Wars films are a translation in several senses of what happened. The main characters can’t speak English, since the action happened long ago. They also can’t be even remotely related to humans, since even if the human race expands into all of our galaxy in the far future, that has nothing to do with what a species from another galaxy in our past would look like.
The Star Wars series has a number of different species from different planets. To make it acceptable to a modern film audience, one of those species has been “translated” to look like humans, just as their language has been translated to English. If you can suspend disbelief enough to pretend that a film set in classical Rome is in English, you can suspend it enough to pretend that the main species of the Star Wars series look like humans, despite the fact that they can’t really look like them.
If it happened in a galaxy far, far away, wouldn’t it had to have happened a long time ago, in order for us to know about it now? 
It makes the movies easier to cast in Hollywood too.
Superdude’s link contradicts this, it seems to me.
::waves hand:: These are not the voids you’re looking for.
I was going to ask if all the Human characters originated on the same planet (or rather, their ancestors did) but I found the entry for Human in the Wookiepedia and it says they all probably originated on Coruscant. The page also lists a couple dozen races, from Alderaanian to Valgauthian.