how to write English speakers talk in French to keep conversation private

[TheWritingGroup]

You'd think this would work, but when I did this, I got a (minor) telling-off.

I've been advised to totally rewrite my last story because the complicated formatting I used was confusing to read. It's apparently pretty easy to write something that's clear to us, the writers, but not to readers who didn't participate in the writing process.

Depending on the situation, you could do the French thing by having it witnessed by some other viewpoint character, and not immediately reveal to the reader what was said. You'd only write down the first sentence or so, and then Viewpoint Person would only record "They kept speaking in French, which was frustrating." The reader doesn't find out what was actually said until after the action this is leading up to.