Thanks for that lead.
I'm in Belgium. I've done searches in French, English and Dutch. I have found a number of trailers that are advertised as "folding", but it seems that, for at least some of them, that just means that the arm that connects to the hitch folds down. I've found other trailers advertised as "folding" that look quite a bit like the one you have pointed to, but none of the photos show what those trailers looks like folded, so am left to guess how far exactly they fold..