I found several English versions of the text (which is from the speech Zamenhof gave in Boulogne-sur-Mer, France, in 1905 at the first World Esperanto Congress)

I found several English versions of the text (which is from the speech Zamenhof gave in Boulogne-sur-Mer, France, in 1905 at the first World Esperanto Congress) by searching for zamenhof "but sincerely" in case anyone is interested.