Von Uexküll is probably best known as someone who is read about (in Heidegger, Deleuze and Guattari, Agamben etc.) rather than someone who is read. Joseph D. O’Neil has made the translation and it should be worth reading.
But the problem is that this would seem to be a new translation of a text that has long been in English: “A Stroll through the World of Animals and Men”, in Instinctive Behavior: The Development of a Modern Concept, New York: International Universities Press, 1957, pp. 5-80.
Two major works remain – to my knowledge – untranslated: Umwelt und Innenwelt der Tiere,Berlin: J. Springer, 1909; and Theoretische Biologie, Berlin: Gebrüder Paetel, 1920.
That really would be something.