What's the difference between: "I'm coming with you." and "I'm going with you."?

really, as a practical thing, none. coming and going are simply different perspectives of the same movement. Which way do you think of the movement, from there or to there? you go to there and come from there. where is your implied "here"? at the destination or the start?

Just the spelling. It means the same thing

Honestly, nothing.

It is hard to explain but they are different. "coming" is accompanying. "going" is the movement.

None really. They can be used interchangeably.

Basically it means the same thing.

Not much, you would probably use 'I'm coming' if the trip were happening straight away, and 'i'm going' if the trip was in the future. Other than that, no real difference.

the 2nd one more like a demand

They're both the same but I'd have to say 'I'm coming with you' is more 'prearranged' so the intention of going with the person where ever they are going has already been established.

'I'm going with you' is more of the decision of the person without prearranging or intending to go with the person in the first place.

spelling