"... The Masoretic text is importantly different from the reading of this verse found in the manuscripts of Isaiah among the Dead Sea Scrolls. In 1QIsaa and 4QIsab, the only two Isaiah manuscripts containing this verse, the relevant phrase is is usually understood as “City of the Sun.” Indeed, as a noun is quite rare, but the other uses in Job 9:7 and Judges 14:18 suggest “sun” as the correct meaning. This reading suggests identifying the city with Heliopolis, since it too means “City of the Sun.” Additionally, although the exact language is different, the city described in Isaiah 19:18 recalls the city in Jeremiah 43:13, called “house of the sun,” also acknowledged as Heliopolis ... what is not clear, at least on a simple examination of the textual differences, is whether the difference is intentional and which should be regarded as the earlier or more original of the two. When we turn to the Old Greek traditions we encounter different readings altogether. The LXX has [a] puzzling phrase ... This reading generates at least two important questions: (1) What is the origin of this reading? (2) Why is 'asedek' transliterated rather than translated? The origin of this reading is a matter of debate on textual, linguistic, and historical grounds. No Hebrew text that could potentially be the Vorlage of this reading is extant, a fact that complicates any attempt to determine the reading’s origin ..."

Hibbard, J. Todd "Isaiah 19:18: A Textual Variant in Light of the Temple of Onias in Egypt" in Holt, Else Kragelund, et al. (eds.) Concerning the Nations: Essays on the Oracles against the Nations in Isaiah, Jeremiah and Ezekiel (pp. 32-52) Bloomsbury T&T Clark, 2015