The Greek that is translated as “(you) foolish people” or “(you) foolish ones” is (back-) translated in a number of ways:

• Ekari: “thought not (having) people”
• Kituba, Sinhala, Marathi, Javanese: “people without sense/understanding/intelligence”
• San Blas Kuna: “people having a dark liver” (“incapable of intelligent, thoughtful behavior”) (See Seat of the Mind for traditional views of “ways of knowing, thinking, and feeling.”)
• Batak Toba: “those short-of-mind” (“mostly referring to stupidity or ignorance in general”)
• Zarma: a word indicating a person who refuses to use the intelligence he has
• Chichewa, Yao: expressions implying intractability and willful opposition to common interests or commonly accepted ideas (source for this and above: Reiling / Swellengrebel)
• Mairasi: “(you are) beeswax” (source: Enggavoter 2004)

See also insane / fool.