What language did the Firbeards and Broadbeams for there names?
 

I've been speculating about what language the Dwarves of the Ered Luin used for there names.

Was it Khuzdul? Since they could use a name from their language that wasn't necessarily their true name, like Azaghal. Elvish? Since they used it . Lastly Adunaic? Since they did have some trade with Men, or was it a mix of all of them?

Your thoughts?

The Firebeard and Broadbeam names are Khuzdul.

Yes, this appears to be in contradiction to what Tolkien said elsewhere about dwarf naming conventions.

It is a slightly difficult issue to reconcile and I am interested to see what theories others have on the matter.

You have mentioned my own personal theory, that they were using Khuzdul words that were descriptive of themselves (I have seen some opine that Azaghal means warrior, but I can't find the reference at this moment) but these were not their true names. Tolkien did note that the dwarves were not always reluctant to teach their language, but that others had difficultly in learning it, so maybe in this matter the dwarves were willing to be a little more open.

That dwarves did teach some elements of their language is evident from the fact that Adunaic was partially based upon Khuzdul, and probably many of the languages of other men probably were as well.

I don't think it's neccesarily a contradiction of Tolkien's. Since it doesn't neccesarily mean they are using there true names. Just a given name, like Thorin or any of the other Mannish names Durin's folk used. Or it could be a description of themselves as you stated.

Also, I forgot to mention the great smiths of the Firebeards Gamil Zirak and Telchar.