In the UK we have "right, I'll let you get on" like you are doing them a favour.
[1] http://scholarworks.sjsu.edu/cgi/viewcontent.cgi?article=405...
"When Vetinari considers the meeting ended, he usually dismisses his visitors with the phrase "don't let me detain you." The inherent implication being that he just might if they let him."
"Right|Okay, I have to leave you (now)+."
I use the "ah" to try to capture the tone and gestures that usually accompany "if faut que j'y aille", a sort resignation and regret. A fiction recognized by both speakers.
> Which is why getting tone right in a foreign language is next to impossible.
Absolutely right. This really is a blind spot that I am cruelly reminded of every time I find myself in an oral actual conversation with an English native speaker.
> I'm guessing you're translating from "il faut que j'y aille" which is politer in French, thanks to the use of the subjunctive.
I usually formulate it like this:
Je vais devoir|dois vous laisser (maintenant).
Je vous laisse.
> In English though, without this grammatical tone-setter, you've basically just told someone that you have something that you consider more important than them. Sometimes that can work, especially when the other person isn't expecting your undivided attention, but other times, not so much.
Indeed, the previous example I gave could also be very harsh when spoken a certain way.
I sometimes add a `because|parce que` and a reason but I am more often than not under the assumption that the other person will think I am making up excuses which would be even ruder.