Quechua!
Cool.
One of my classmates (from Guatemala) speaks Nahuatl and several other Meso-American native languages.
I know bits and pieces of Hebrew, too, which is actually related to Tigrinya (they are both Semitic languages).
Yiddish I don't know at all, though when I was a kid I used to think that one's Yiddish skills grew as one aged. My great-grandparents spoke it fluently, grandparents knew lots of phrases, parents know a couple of phrases and some odd words, and I knew none. Gotta love the logic of kids!
I know no Hawaiian but know a bit about its sound system, which is extremely simple, containing very few consonants, which is why English words become largely unrecognizable when borrowed! (example: Merry Christmas --> Mele Kalikimaka)
Hawaiian only has the following consonants: p, k, h, m, n, w, l and ? (glottal stop). It also only permits sequences of consonant-vowel.
In other words, "Christmas" is a tongue-twister in and of itself for Hawaiian speakers! The 2 s's become k's, the r becomes l, and all the consonant-consonant sequences are broken up by vowels. It actually is an extremely predictable and regular pattern, if you know what you're looking for!
Link to English/Hawaiian loan words, and a good, if simplified, introduction to phonology (the study of how sounds pattern in human language):
http://www.ic.arizona.edu/~lsp/Phonology.html