I'm nowhere near fluent in Japanese, so I'm not the best person to get into it. I do have a couple good friends who are native speakers or expats with a very high level of understanding. A good mate runs a bilingual IT firm in Tokyo, and can handle even technical/legal Japanese to a pretty high level.
Sometimes I've asked, "How do I say XYZ?" and there's no real way to say it without describing it. To go back the other way, what would the English equivalent of "domo" or "daijobu" be? Daijobu is something like "don't sweat it", but that's not quite right. I'm not sure there's anything quite like domo.
But, that's common enough in other languages. German doesn't "cheers", which is a pretty useful and versatile British English word, but that's not what I mean here. From my general understanding, it's very hard to put together appropriate forms of disagreement in Japanese. Like, it might not possible to say something like, "You're wrong, but I respect the sentiment", or "Agree to disagree."
I'm not sure on those specific examples. I know one of the first things people learn about doing business in Japan is you'll rarely hear "no" from a subordinate, so you have to be very aware of something like, "That might be difficult..." - that might mean it's impossible.
Not entirely sure - I've spent a bit of time living and working in a lot of places, and picked up touches of a fair few languages. I've had people translate for me to some extent or other in German, Dutch, Spanish, Mandarin, and Japanese. By far, the most stumbling and "that's hard to say" I got was in Japanese. I'd actually be curious to have someone more skilled with the language elaborate more to see if I'm on the mark here.
That said, the character of the Japanese language is really beautiful - I love reading Japanese literature translated into English. You'll commonly see a very factual, plain description, followed by a very profound beautiful statement mixed in with minimal transition. Eiji Yoshikawa's "Musashi" is pretty much a must-read for anyone talented who feels some friction with more mainstream and normal society.