We now have JRRT on
Uruk-hai 'Orc-folk' (as has been theoried by some) and in a post-Lord of the Rings context (his idea at least at the time of writing the following anyway). The context in general is the Black Speech on the Ring, and after a note
B krimp-, tie, bind, there is the following (as it appears in PE17)
'The Black Speech was not intentionally modeled on any style, but was meant to be self-consistent, very different from Elvish, yet organized and expressive, as would be expected of a device of Sauron before his complete corruption. It was evidently an agglutinative language, and the verbal system must have included pronominal suffixes expressing the object, as well as those indicating the subject: -ul is a pl. objective, translated 'them', and -ūk an element meaning 'the whole, all (thrakatalūk I 267 is a misprint for -ulūk, a correctly written in the flame letters). The stem burz 'dark' is also found in the later Lugbūrz = Barad-dūr; in the archaic ring-inscription burzumishi is evidently made up of this stem + a particularizing suffix or 'article' um, and an enclitic 'preposition' ish 'in, inside'. The debased form of the B. S. which survived in the Third Age only in the Dark Tower is seen in a few names (as Uruk-hai 'Orc-folk') and the fragment of vituperation uttered by one of Grishnakh's companions, emissaries from Sauron. I have tried to play fair linguistically, and it is meant to have a meaning and not to be a mere casual group of nasty noises, though an accurate translation would even nowadays only be printable in the higher and artistically more advanced forms of literature. According to my taste such things are best left to Orcs, ancient and modern.'
The Editorial note explains:
'This is from the carbon copy of a letter to Mr. W. R. Matthews (dated 13-15 June 1964), which Tolkien placed in the same file with the manuscript of 'Words, Phrases and Passages'.
The editorial note is longer, explaining agglutinating language and other things.