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"). 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.

UPDATE 2:

This seems to be somewhat confirmed, though the last specific details are from an uncited and later deleted Wookieepedia 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)

The Wookieepedia article on Nien Nunb confirms this, linking to this article.

And this clone of an older Wookieepedia page for Kipsang Rotich said: