It is recorded that the tribe of the Hebrews, the ancestors of modern Israel, were at war with an enemy that was ethnically similar to them, and tried to infiltrate them. Since spying was a big problem, a lot of effort was put into a solution, which was also dutifully reported. The Hebrews noticed that their enemy lacked a sound in their language that the Hebrews did have: what is “SH” in modern English. This group substituted “s.” And so they asked any suspected spy to pronounce a word with that sound in it, and if he couldn't do it, they killed him. This test of ferreting out by some word or action that an outsider cannot readily reproduce is now known by the word that the Hebrews did for their test, “shibboleth.” “shibboleth” means either “ear of corn” or “torrent of water” in Hebrew. The best the infiltrating group could manage was “sibolis,” and someone pronouncing it that way tended to be stabbed on the grounds that they were a spy.
Wikipedia records the use of shibboleths in war, because the cost of being infiltrated by an enemy group is quite high. They give the quick examples of the world war II, such as American example “Flash. Thunder. Welcome.” (America does have people of German and Japanese origin.) The sentence would have been pronounced by a German speaker as “Flash. Thunder. Velcome.” and by a Japanese speaker as “Frash. Thunda. Wercome.” A group approaching while shouting an “enemy” pronunciation would have been fired upon. The Australians had a similar shibboleth designed to root out Japanese speakers, since the German army was too far to menace Australia. They used “Wooloomaloo,” which would be incorrectly pronounced “Wurumaru.”
I speak English, American style, and Spanish. This is quite understandable for me, since I am an American of southwestern origin, English being America's standard language, and Spanish being the most common language of America's southern neighbor, Mexico.. It has left me wondering which shibboleths I could manage, and which ones I couldn't. Also, if there are anti-American shibboleths in most languages. I note that I can reproduce a few sounds that don't exist in my own native language, such as “ж” (which is a guttural sound vaguely like clearing your throat and would be badly approximated by the English “ch” ) which is odd. I may have picked this up from one of my father's friends who spoke Hebrew, Yiddish, or Greek, all languages which do have this sound.
I can immediately think of one anti-English shibboleth offhand. Korean has a sound that is halfway between what is “k” and “g” in my language. I cannot manage to make this sound, and so a word or phrase with one or more instances of this would make a good anti-American shibboleth. A person who was raised speaking English would fail the test, even if they were ethnically Korean.
Spanish (and I think also French) speakers have a “rolled R” that is hard for English speakers to reproduce. German has “ж.” Russian is a little short on concents, and has yet more “ж.”. A few African languages have a “throat click.” The Nordic languages have a few vowels that aren't in English, like “Ø.” Finnish has an especially easy time of this, and has a shibboleth that literally can't be said by anyone whose native language is anything other than Finnish. (It's their word for “steamroller.” It involves several “Øs,” a “hj,” and several other sounds that involve bending the mouth in ways that my mouth distinctly will not bend. A non-native speaker can manage a close enough representation to be understood.)
Speakers of many Asian languages will have a harder time coming up with shibboleths, because most sounds in their languages also exist in English. Speakers of the two big Chinese languages can hope to confound with their tonal system (in which, say “shi” with a rising tone means something differently than “shi” with a falling tone. ) Mandarin Chinese, spoken in northern China, has four distinct tones, and Cantonese Chinese, common in southern China, has six. A tonal based shibboleth is a bad idea, because the tones aren't hard to imitate for speakers of nontonal languages, such as English. A novice speaker might mix them up, but would still manage if their life was on the line. Thai and Vietnamese have some odd letters recorded, but I haven't heard enough of these languages spoken to determine if they represent sounds that aren't in English.
Japanese speakers would have a very hard time coming up with an English detecting shibboleth, since every sound in Japanese is also in English, while the reverse is not true. (although the sound transcribed as “r” is actually halfway between “r” and “l,” but that wouldn't be terribly effective due to an English “r” and an English “l” both being heard as the “r” sound in Japanese.) The only angle I could think of is that Japanese is sensitive to vowel length, in which “tan” and “taaaaan” are two different words. They would have to write a sentence where getting the vowel lengths wrong would have an immensely humorous (or nonsensical) implication.
The last thought is that a shibboleth need not be a word, but could also be an action. There was a supposed anti-Jewish shibboleth practiced by the nazis in which they would leave a person in a room with coffee and sugar cubes. They seemed to believe that a non-Jewish German person would put the cube in the coffee, stir, and then drink it, while a Jewish person would put the cube in their mouth and then drink the coffee. I disbelieve the truth and effectiveness of the test because I have never heard of any person, Jewish or otherwise, performing the second action. In fact, I know several Jewish people personally, and given a cup of coffee and a sugar cube, they all put the cube in the coffee, stir, and drink, although this may be because I was born at least a generation after the nazis, who murdered everyone who put the cube in their mouth, Jewish or otherwise. And anyone they thought was Jewish. And anyone who disagreed with their murderous policies. And anyone they disliked and could get a hold of, period.
Verbal shibboleths work because of the tenancy of adults to either mishear or be unable to reproduce any sound not present in a language they learned in early childhood, but action shibboleths only work if the subject is unaware of being tested and is unaware of the potential implications of their action. And of course, the main problem with a war shibboleth is that it detects a person's native language and/or culture, but not their true loyalty. The “Flash Thunder Welcome” test would be “failed” by an American soldier of German Jewish origin or Japanese origin, despite the total loyalty of this hypothetical man to the United States. It is recorded that some American soldiers of German Jewish origin did in fact have to quickly explain their loyalty to the United States by other means.
Are there any shibboleths to detect members of your group from other groups? Or the other way around?