Shibboleth - According to Wikipedia - A shibboleth (/ˈʃɪbəlɛθ/[1] or /ˈʃɪbələθ/[2]) is a word or custom whose variations in pronunciation or style can be used to differentiate members of ingroups from those of outgroups
Basically it is something you know because you have lived somewhere and have intimate knowledge of it. You will not get it by reading a book about it, or conversing with a few people from there.
For example, this is a shibboleth -
So what would be a Pakistani shibboleth? If someone was lying about being Pakistani, is there something you can use to figure out if the person is indeed Pakistani? Obviously age and background plays an important role here.