A shibboleth is a password or test phrase, particularly one that distinguishes the group membership of the one required to pass the test. Shibboleth comes from the Hebrew for “torrent” or “stream” (or perhaps “ear of grain”), and the word's usage as a password was recorded in the Bible. The Ephraimites had no “sh” sound in their language, an unfortunate shortcoming of which the Gileadites availed . . .
The following passage is from the book of Judges, chapter 12, verses 5-6 (New International Version):
5The Gileadites captured the fords of the Jordan leading to Ephraim, and whenever a survivor of Ephraim said, “Let me cross over”, the men of Gilead asked him, “Are you an Ephraimite ?” If he replied, “No”,
6they said, “All right, say Shibboleth.” If he said, “Sibboleth” because he could not pronounce the word correctly, they seized him and killed him at the fords of the Jordan. Forty-two thousand Ephraimites were killed at that time.
J.M. Guil submits an example from Catalan:
Setze jutges d'un jutjat mengen fetge d'un penjat. Si el penjat es despengés, menjaria els setze fetges dels setze jutges que el van penjar.
[Sixteen judges from a court eat a hanged man's kidney. Should the hanged man “unhang” himself, he would eat the sixteen kidneys from the sixteen judges who hanged him.]
He explains the origin of the passphrase:
The story goes that this sentence was coined during the Spanish Succession War (ending in 1714). As there were frequent skirmishes at night between Catalan defenders and Spanish besiegers of Barcelona, a password that Castilian throats could not reproduce easily was needed. And frankly, the sentence is full of at least three different sounds which Spanish-speaking people pronounce only with the greatest difficulty.
He also mentions that a musical group during Franco's régime adopted the name Els Setze Jutges.