I wonder if shall/will is a problem that foreign speakers of English struggle with? The distinction is largely nuance, but it makes a big difference to me which word the speaker chooses. "Shall" expresses determination, "will" is normally just intention. But "You shall go to the ball" means something quite different from "You will go to the ball".
In spoken English we often conflate them: "I'll have bacon and eggs." It's not clear whether the speaker is expressing defiance ("Aren't you having black pudding?") or simple intention. I don't know how you learn nuance in English speech, but I think humour must be part of the training.
Do people even use “Shall” in the vernacular anymore? If someone used that word in a work meeting I’d probably do a double take even though I’d understand what they meant. At least in American English.
I will drop a "shall" occasionally if I'm in the mood. "Shall we take a walk?", rather than the "Should we take a walk?" or even "Do you want to take a walk together?" It can lend itself a certain air of grace if delivered correctly. Then again, I'm an American mom in her late 30s - it might not have the same reception if said by anyone else.
I'm no fan of Churchill, but he was a great rhetorician, and very quick off-the-cuff:
"Sir, you are drunk."
"Yes madam; and you are ugly, but in the morning I shall be sober."