One thing thats always bothered me is the elvish ruins on the mysterious Doors of Durin and how they contain such a simple riddle to open the door. Now, I understand it was Narvi and Celebrimbor, I think, who built it together. Which would explain the elvish ruins. But....why?
A) Why would the dwarves want to use a simple elvish phrase in a pretty simple riddle to get inside one of their most treasured cities? True this was when they were friendly with elves, but there were other entrances to Moria...did they also need an elvish riddle?
And B) I also read that dwarves were good with languages....but how true is this? Of course you had those who would communicate with the elves for trade and what not, and if so, does that mean most dwarves, of all castes, spoke enough elvish that it was no concern to put it on a mountainside door? I'm sure there's a few but I can't think of a specific example of a dwarf speaking elvish to an elf, only the broad stuff about their interactions.
And C) I mean...come on. The riddle. Yeah it's clever and all, but if you're a riddle master, that's a fairly simple one to analyze. Don't most hobbits love riddles (not just Bilbo)? And tbh I'd think Gandalf would be able to figure it out, if not know already. I know the dwarves are more clever than that...