The most complicated twister I know is in Russian:

  Карл у Клары украл кораллы, а Клара у Карла украла кларнет

(Karl u Klary ukral korally, a Klara u Karla ukrala klarniet — Karl stole corals from Klara and Klara stole a clarinet from Karl). Audio: http://en.wikipedia.org/wiki/File:Russian_tongue-twister_-_K...

Alternating "rl" and "lar" make it tricky.

What does it mean? Three sad tigers...

Three sad tigers ate wheat in a wheat field.

something something ate corn in a cornfield?