There was at least one known example of real Earth language used by G-canon (e.g., movies). In Episode VI (ROTJ), Sullustese language - or at least, lines from it - was indeed using a real non-English language.
By the way, the most commonly rumored answer to this question (Ewoks speaking Tagalog) is actually not true. They had some Tagalog words mixed in but it wasn't actual Tagalog speech.
UPDATE: Found the details for Sullustese - and indeed, as I remembered, that same source dispels the Tagalog rumor which is why I recalled both simultaneously.
As per this forum comment (in a thread "Did I hear the Ewoks speak Filipino"): http://forum.blueharvest.net/index.php?showtopic=4485 . Spelling and grammar corrected by me.
If you listen to the Return OF The Jedi DVD audio Commentary, Sound Designer Ben Burtt explains that native language sounds were used to form the language of many Star Wars species so you probably hear specific words but it seems, from what Mr. Burtt says, that it is randomly joined words rather than dialogue in another language.
The only exception to this is Lando Calrissian's Falcon co-pilot in Return of the Jedi, the Sullaston named Nien Nunb. His dialogue is translated directly into the young actor who played him's native language.
This seems to be somewhat confirmed, though the last specific details are from uncited and later deleted Wookiepedia article, so caveat emptor (they do seem to match most of the other info I was able to find so I would consider them trustworthy enough):
Nien Nunb IMDB page says:
Star Wars: Episode VI - Return of the Jedi (1983)
Played by Richard Bonehill / Mike Quinn / Kipsang Rotich
And digging more, Kipsang Rotich's IMDB page says:
Actor (1 title)
1983 Star Wars: Episode VI - Return of the Jedi
Nien Nunb (voice) (uncredited)
Wookiepedia article on Nien Nunb confirms this, linking to this article.
And this clone of older Wookiepedia page for Kipsang Rotich said:
Kipsang Rotich was an African student who voiced Nien Nunb in Star Wars Episode VI: Return of the Jedi.
He used his native tongue of Haya as if it were Sullustese. He was not credited in the movie.
Furthermore, it was noted that when Rotich had read the lines for Nien Nunb, they translated (in another language) into "One thousand herds of elephants are standing on my foot".
But not all of Nien Nunb's lines are in the Haya language, which is not spoken in Kenya but rather neighboring Tanzania. The very first thing he says before the attack is in the native tongue of Kenya's biggest tribe, the Kikuyu, and it translates to "All of you over there, come here."
By his surname, Rotich is from the Kipsigis subtribe of Kenya's Kalenjin tribe in the Great Rift Valley -- where the Kipsigis live alongside Kikuyus and would therefore be likely to speak Kikuyu as well as their own unrelated tribal tongue.
He did many lines in Haya, because no one thought anyone would understand it, but they did.