[acqq]

For the reference, the Latin word is monstrum, and like I've said, there were surely people using that word while living on the territory of today's England long before Beowulf was written.

I'm quite sure no Japanese were living there either before or at the time Beowulf was written. That's the difference that I consider jarring, not the fact that the newer language is the language of the translation. Even in English, not all words have the same "weight" -- some simply "sound" new and have certain "modern" connotations and some don't. Some imply origin from one place, some from another, etc. It's simply more complex than "the whole English is newer, who cares" approach.

My favorite example from 1490 is:

"In this book, Caxton tells the story of some merchants from the North of England trying to buy eggs from a woman in the South of England. The northerner uses the word egges, derived from Old Norse, but the Southern woman, who uses the word eyren from the Old English, does not understand. A humorous misunderstanding ensues."

https://www.bl.uk/learning/timeline/item126611.html