In Greek, the word " Τρωγοδύται " or Trogodytai means "cave dweller" or "cave goer". Historically, these "Trogodytai" were mentioned by several ancient writers and historians like Herodotus, Strabo, Pliny and some others.

The problem is each of the historians that wrote about those so-called cave dwellers put them in different places, from Herodotus who places "Trogodytes" as being people living roughly in Lybia( he describes them as "the ones being hunted by the Garamantes" and "reptile, snakes and lizard eaters" with a language unlike any he heard before). However, Strabo, in Geographica, places a tribe of Trogodytes living in Scythia Minor, around the Getae, Daciae and the Tomis colony. However, Athenaeus writes about Pythagoras who is said to have written about "Trogodytes" who were living around the Red Sea coast, talking about their instruments. Athenaeus also writes about how Euphorion wrote their sambuca which was a string instruments, was similar to that of the Parthians. Eusebius even says "Trogodytes" invented the sambuca.

Flavius Josephus, a 1st century Roman-Jewish writer, also mentions the Trogodytes. He writes in Antiquities that Abraham's sons settled "Trogooditis" and Arabia Felix. Arabia Felix refers to mean the southern coast of the Arabian Peninsula, and "Trogoditis" is nowadays assumed to mean the Red Sea coast.

As far as I am aware, there is no consensus over who really are these "trogodytes", because the term has been used to refer to several different groups for whom the only common denominator was that "they supposedly lived in caves". Living in caves was a... common occurance, especially in the Sahara and Arabia(to the point where "Africa" is considered by some to have come from the berber word "Ifri"', which means "cave"). I personally believe Plutarch was reffering to some sort of Red Sea Coast dwelling peoples, given it would make sense for Cleopatra to understand the language of a people living close to her realm and on important trade routes.