Translation:They are splendid.
Its not necessarily just to describe the state of a person. I'll occasionally use splended (once every week or every other week), typically in the situation where someone presents a bad situation "Hey, the lawnmower just broke" and I'll respond "Oh, thats just splended isn't it? Right when the car broke down too."
Only other times I've used it was mockingly "Why good sir, I do believe we had quite a splended time. Thank you sir, I tip my hat to you."
Being a bad speaker of Japanese but having lived in Japan for many years I don't remember it being used for people. The only time I hear it is for buildings and I wouldn't translate it as splendid which is a favourite of British English but more as stately, magnificent or grand.