The Greek that is translated into English as “vain” or “in vain” in English is (back-) translated in various ways:

• Guhu-Samane: “with the front teeth of their mouths they worship me” (“‘In vain’ caused puzzlement [because] why should their efforts to worship God produce no results, try as they may? [But the idiom] ‘with the front teeth of their mouths they worship me’ comes from the picture of one who is making a pretense at eating food, hence their deceit is apparent.’ Source: Ernest L. Richert in Notes on Translation December 1963: p. 4-7; reprinted in The Bible Translator 1965, p. 198ff. )
• Cashibo-Cacataibo: “say I am important, but they do not believe it”
• Kekchí: “has no meaning when they praise me”
• Toraja-Sa’dan, Pamona: “uselessly”
• Copainalá Zoque: “uselessly they remember”
• Farefare: “their religion is their mouth”
• Southern Subanen: “their worship has no meaning”
• Tzotzil: “they say they love me, but this means nothing”
• Southern Bobo Madaré: “they worship me but they do not mean what they say”
• Central Mazahua: “it is of no value that they honor me”
• San Blas Kuna: “their thinking is not in their hearts” (source for this and above: Bratcher / Nida)
• Mairasi: “tribute of theirs for me [which] will-be-on-their-own” (source: Enggavoter 2004)