How would British or French views and assurances to the Germans be transmitted in a way that all those reasonably-minded Germans could then have used as an argument against their hawks?

You seem to have even less of an idea about those times than I. Short answer, as I gave before: newspapers. France and Germany have had a very intense relation for centuries; news, like people, traveled very quickly and without effective censorship. (In fact there was a substantial left-wing movement in Germany, profoundly critical of militarism, but eventually feeling deprived of arguments [besides being bullied by the nationalists - not by the government alone]. See e.g. the election of 1912 and the subsequent events.) News from Britain were and are studied eagerly on the continent as well; the other direction seemed to be somewhat blocked, by lack of interest.

The League of Nations was a joke because they failed to act in accordance with its founding principles

The reason was of course that all actors had their own agendas, and the consciousness for world-wide issues was underdeveloped. My impression is that it is constantly improving, though not as quickly as it should. Anyway, we have no other option, for the four reasons I gave, and many others (- think of trade regulations, research, internet spying, fight against monopolies and crime including tax evasion, copyright, ...). The idea of strong and strong-minded nations is the real joke nowadays.

A "literal World Police" differs from any self-appointed (and thus rightly vilified) one by its democratic legitimation and rule of law. A long way, but there is no other one.

Kaiser's fleet etc.: not my own theory; let those discuss who think they have the information. We agreed that the war was not about Belgium, otherwise it would have been best to let the German army pass through it, against payment of a reasonable fee for the road damages ... haha.

Kuwait: sorry, too much of a digression.