Translation:They are splendid.
Heh heh...kind of an archaic word...like Olde English...I think he is AMIABLE...
Well I think you are cool for saying it!
I'm not Japanese though, so you're still a laughing stock.
Which is much how I would react if one of my students of English dropped the word splendid.
I have started using Anki in addition to duolingo for more variability, also started listening to live Japanese radio while at work. Even though I only understand about one in every 10 words you start to learn common phrases and tricks used in speech.
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."
You dont use older splendid words? Up your vocab yo. Spice up your vernacular.