I had the reverse of that situation, a few years ago. We had parked in a French Aire, to have our lunch, but, planned to move on, after lunch. We got the last space available. A French registered motorhome arrived, but, couldn't get parked in a "bay", because there were none left available.
My schoolboy French is very limited, but, I spent five minutes, working out how I could tell the other driver, in French, that we would be leaving shortly, and, he could then have our space.
When I spoke to the "French" driver, giving my carefully rehearsed speech, he looked baffled. I assumed that I had got it all wrong, which would have been no surprise.
It turned out, he was a Brit, who lived in France, owned a French Registered Motorhome, but, spoke even less French than I did!