I found an interesting article on Tolkien’s creation of his languages, Tolkien’s Not-So-Secret Vice.
Having been a language lover in my youth (though I never learned a lot in most of them), I particularly was delighted with these paragraphs:
One thing was important to Tolkien. Languages should be beautiful. Their sound should be pleasing. Tolkien tasted languages, and his taste was finely tuned. Latin, Spanish and Gothic were pleasing. Greek was great. Italian was wonderful. But French, often hailed as a beautiful language, gave him little pleasure.
But heaven itself was called Welsh. In his essay “English and Welsh”, Tolkien recalls how he once saw the words Adeiladwyd 1887 (It was built 1887) cut on a stone-slab. It was a revelation of beauty. “It pierced my linguistic heart,” he recalls. It turned out that Welsh was full of such wonderful words. Tolkien found it difficult to communicate to others what really was so great about them, but in his essay he makes an honest attempt: “Most English-speaking people…will admit that cellar door is ‘beautiful’, especially if dissociated from its sense (and from its spelling). More beautiful than, say, sky, and far more beautiful than beautiful. Well then, in Welsh for me cellar doors are extraordinarily frequent, and moving to the higher dimension, the words in which there is pleasure in the contemplation of the association of form and sense are abundant.” He then lists concrete examples like Welsh wybren being “more pleasing” than English sky. -MC p. 190-193.
But there were more pleasures in store for young Tolkien. One day he found…a Finnish grammar!!! He soon found himself in phonaesthetic ecstasy. “It was like discovering a complete wine-cellar filled with bottles of an amazing wine of a kind and flavour never tasted before. It quite intoxicated me” (Letters:214). High on Finnish he scrapped his latest project (“make your own Germanic language”), for now he had found more powerful inspirations.