Kind of. Sindarin was based on Welsh, and Quenya derived from Finnish. The mythology was certainly based on Norse and Old English folk tales.
A lot of modern Welsh words are different spellings from how the word is said commonly elsewhere...usually English words, but could of course be French or Spanish etc words if that is the recognised name for something. Just as the English language adopts words from other languages. Don't want to be like the French who attempt to freeze their language and then discover that is impossible. As for older words, the British have swirled round the British Isles for thousands of years....hardly surprising if words are shared in different regions. Some English words are very similar to Indian dialects....and that predates the Raj...just that over the millennia people have travelled from the subcontinent and settled in Europe and GB. Linguists look for certain words to see if people have migrated....usually the words for water, mother and father show similarities.
I lived in Wales for 25 years, always wondered why the kitchen sink was referred to as the bosh? @Saint Helen
4. South Wales dialect a kitchen sink or wash basin Collins English Dictionary. Copyright © HarperCollins Publishers
A common term used in the South Wales mining valleys for a Belfast sink usually found outside on the Bailey or in a skullery. Now I have to find out what a Belfast sink and a Bailey is!
I'm probably from too far west. I asked a few people in work and only one had heard it before - her grandmother used to use it. She was from Merthyr.