Roughly it would be pronounced Chal-chi-wit-lee-kway-ya-cat-tchl -- the "tl" in nahuatl is a sound made by placing the tip of your tongue on the roof of your mouth and kind of doing a sort of click-hiss out the sides of your mouth. Very easy once you know how.
Sadly it’s apparently fake. There’s no documented “traditional” Nahuatl name for the gulf, and one linguist has spoken up that this seems to be true of all the languages of the gulf coast: in his opinion they all probably called it “the sea” in their respective languages.
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https://www.youtube.com/watch?v=JONVfWtmTig
https://bsky.app/profile/islandofreil.bsky.social/post/3li5cfb53lk2g
Chal-chee-oo-tlee-kweh-je-kah-tl
“Chal-CHEE-ooh-tlee-quay”
Is the Spanish pronunciation but you can use it for the English too.
Chalchiuhtlicue was the Aztec goddess of water, rivers, and oceans.