Three gods answer only in a language you don't know; one question each finds the truth
Three gods, A, B, and C, are called True, False, and Random, in some order. True always answers truthfully, False always lies, and Random answers truthfully or falsely by pure chance. They understand English but answer only 'da' or 'ja', and you don't know which word means yes and which means no. You may ask exactly three yes-or-no questions, each addressed to exactly one god. How do you determine which god is which?
Reveal the answer
Logician Raymond Smullyan and philosopher George Boolos showed it's solvable using self-referential, counterfactual questions, for example asking a god what another god would say to a given question, which lets you extract reliable information even without knowing the meaning of 'da' and 'ja' or who is lying. Boolos published a full worked solution in 1996, building on question structures Smullyan had developed for simpler knights-and-knaves puzzles.
— George Boolos, The Hardest Logic Puzzle Ever — The Harvard Review of Philosophy, 1996