Are there words which sounds very similar in different languages, and which are proven not to be the result of cultural exchange? For example, we know most words related to technology comes from English, so that's probably why computer is computadora in Spanish and kompyuta in Japanese. But is there proof that words coming from cultures isolated from each other having very similar sounds? (not counting onomatopoeias which are supposed to imitate how a noise sounds) . If so, can you give me some examples?
I think False Cognates : https://en.wikipedia.org/wiki/False_cognate might be what you are looking for.
There is a Facebook group Linguistic Coincidences & Curiosities the members of which have been collecting such false cognates for years already. My favourites are the Latin and Malaysian "dua" which means "two" in both languages, there are also "reverse" coincidences like in Polish "tak" means "yes", and in Indonesian it means "no".
I will give you a perfect example from Turkish and Japanese. Turkish iyi and Japanese ii いい are read totally same. And more interestingly both of them have the very same meaning good. If you add Ural-Altaic hyptothesis, one can totally jump to the conclusion those 2 words have something in common.
I don't know story of the いい but I can tell about the iyi. In Istanbul Turkish it is iyi, but in most of the Anatolian accents it is eyi or eyü. It comes from the old Turkic edgü->eḏgü->eygü->eyü->eyi->iyi.
So actually both words have nothing in common except meaning.
The Nahuatl word teotl meaning god makes me think of the ancient greek theos, which has the same meaning [Theos — From Proto-Hellenic *tʰehós (whence also Mycenaean Greek 𐀳𐀃 (te-o)), a thematicization of Proto-Indo-European *dʰéh₁s, s-suffixed noun derived from *dʰeh₁- (“to do, to put, to place”)].
Or even the Nahuatl verb cochi meaning to sleep reminds me of the french verb coucher, which means to lay down (although they are pronounced a bit differently, since the french "ch" sounds more like a "sh") , and is often used as to say to go to bed (e.g. "Je me couche" -> "I'm going to bed").