Like I said in another thread, Tolkien wrote the LOTR as a linguistic experiment, not to write the greatest epic of all time (which is just became anyway). He set out to prove that language defines culture. If your language is harsh, your culture is harsh. If your language is soft, flowey, romantic, your culture is the same way. Take a look at German and Russian. They are tough languages, very strong and "rough". German and Russian culture and history is essentially the same way. Then take a look at French language and look at French culture. They pride themselves on romance and the sound of their language to someone who doesnt speak french clearly represents that.

Elvish is a romantic language, soft and light because elves themselves are like that. The language of Mordor is gutteral and rough because Mordor is like that. Tolkien spent his whole life on the study of language and communication. It's no wonder he put such work in the languages of the LOTR. It's also no wonder that we would see resemblences of Gaelic or other real languages too, considering he grew up in Britain.