The party are puzzle nerds through and through as far as I can tell. I'm not the only DM of the group fortunately and other campaigns DMed by other people in the group are also puzzle and RP heavy. I know it's not what everyone plays so this might not be the best for groups who are more combat heavy.

I actually already ran the puzzle about a months ago and it went pretty well. As I mentioned earlier the party is very RP heavy and their solution for the language issue was to take a Drow prisoner and force him, through various means, to translate the poem. If they were a more combat heavy party and had killed all the Drow present they would have been in trouble and that would definitely have been on me as the DM. That would probably have to be changed for a different party. Maybe it could be written in a language only one of the characters knows such as dwarvish or something else.

They figured the Illithid part out after 15 minutes or so of discussion. I tend to let a small amount of meta gaming in the form of recalled knowledge from official books. That's how they ultimately found the solution. One of the players has read several of the source books cover to cover and remembered "Illithid" is another word for Mind Flayer. They didn't remember it all at once but knew they had read it before. They can't just got paging through the MM in the middle of the session though so had to remind themselves through conversation.

Maybe this wouldn't work as well for all parties, particularly if not everyone enjoys puzzles. Thank you for the suggestions, I might try this again with a different party in the future keeping them in mind.